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Risk-Based Waste Classification in California (1999)

Chapter: Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report

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Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Appendix D
California Environmental Protection Agency Department of Toxic Substances Control (DTSC) Letter of Introduction, Overview, Concept Paper, and Appendices 1–4 from DTSC Report

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
This page in the original is blank.
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Risk-Based Criteria for Non-RCRA Hazardous Waste

Volume 1 of 2

A Report to the National Research Council Introducing Proposed Changes to the Definition of Hazardous Waste in the California Code of Regulations

Prepared by

Human and Ecological Risk Division and Hazardous Materials Laboratory of the Science, Pollution Prevention, and Technology Program Department of Toxic Substances Control Environmental Protection Agency State of California

February 27, 1998

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Risk-Based Criteria for Non-RCRA Hazardous Waste

Table of Contents (revised, August 26, 1998)

Tab*Title

Page

Volume 1

 

1 Overview and Letter of Introduction

1

2 Issues

10

3 Concept Paper. California's Non-RCRA Waste Classification System: Analysis and Proposed Revisions (with 4 Appendices)

13

4 TTLC Risk Assessment Models

75

4a Documents Describing Results and Input Values

76

4a1 CalTOX Adaptations for Derivation of Exit and Upper TTLC Criteria

78

4a2 CalTOX Version 2.3: Description of Modifications and Revisions

105

4a3 CalTOX: A Multimedia Total Exposure Model for Hazardous-Waste Sites

181

4a4 Analysis of Results and input Values of the Upper and Lower TTLCs Computed Using the CalTOX Model

520

4a5 The Distribution of California Landscape Variables for CalTOX

555

4a6 Parameter Values and Ranges for CalTOX

591

4a7 Draft Final Report: Intermedia Transfer Factors for Contaminants Found at Hazardous Waste Sites

647

I. Vinyl chloride

647

II. 2,3,7,8-Tetrachlorodibenzo-p-dioxin

687

III. Trichloroethylene

730

Volume 2

 

4b The DTSC Lead Risk Assessment Spreadsheet

775

4c The Preliminary Endangerment Assessment Model

784

4d De Novo Ecological Risk Assessments

844

5 Detection Limits and Background Level

858

5a Ambient and Background Concentrations

859

5b Analytical Issues

864

6 Concept Paper. Evaluation of the Suitability of the Federal Toxicity Characteristic Leaching Procedure (TCLP) in Lieu of California's Waste Extraction Test (WET)

869

(7) Comparison of California's Waste Extraction Test (WET) and the U.S. EPA's Toxicity Characteristic Leaching Procedure (TCLP)

880

(8) Leaching Potential of Persistent and Bioaccumulative Toxic Substances in Municipal Solid Waste Landfills

964

(9) Comparison of Short-term Extraction Tests with Extraction Using Municipal Solid Waste Leachates

1046

(10) Supplement to the RSU Extraction Test Project Summary Report: Phase 1

1078

(11) Supplement to the RSU Extraction Test Project Summary Report: Phase 2

1255

(11a) Tables for RSU Phase 2

1285

(11b) Figures for RSU Phase 2

1331

(11c) Appendices: Commercial Uses of Elements

1397

7 (12) Subtitle D Landfill Composite Liner Protection Factor

1485

* numbers in () correspond to Cal/EPA's original numbering system and may be referred to elsewhere in the document

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

1. Overview

California's system for classifying wastes consists of two principal elements. One element is the federal system created under the authority of the Resource Conservation and Recovery Act (RCRA). As an authorized state, California has promulgated regulations mirroring those developed by the U.S. EPA under RCRA. These regulations are not part of this review. The second element is the non-RCRA system, which goes beyond and complements the RCRA system. The Department of Toxic Substances Control (Department) has undertaken an update of its entire non-RCRA waste scheme. The purpose of this update is to re-assess the need for the non-RCRA system, to update the scientific underpinnings of the system as needed, and to simplify the system where possible by eliminating redundancy and overlap, rewording confusing sections of regulation, and eliminating elements that have outlived their usefulness. It is the scientific basis for the proposed revised waste classification system that we are asking you to review.

California's waste classification differs from the federal system in several ways: California has a list of approximately 800 chemicals which, when present in a waste, make it presumptively hazardous. However, a generator can use testing or knowledge to show that a waste containing one or more of the chemicals on the presumptive list does not exhibit a hazardous characteristic. Thus, California's non-RCRA system does not have ''listed'' hazardous wastes in the same way that the RCRA system does. California's non-RCRA system, like the RCRA system, includes the four hazardous characteristics of reactivity, ignitability, corrosivity, and toxicity. The first two are identical in the RCRA and non-RCRA systems. California's corresivity characteristic is slightly broader in that it includes corrosive solids. However, the characteristic that is most different between the two systems, and the one that is the subject of this review, is the toxicity characteristic.

California's existing classification system comprises eight criteria for the toxicity characteristic (see table below). The Department proposes to retain all eight of the criteria, but to revise five of them. At present a single tier of thresholds creates a single tier of regulated waste: hazardous waste. A key aspect of the proposed changes is to add a second tier of regulatory thresholds for each of the first five criteria. This would create two tiers of regulated waste. The upper tier, to be called hazardous waste, would include the most toxic wastes (along with corrosive, ignitable, and reactive wastes). The lower tier would include wastes that are moderately toxic. The principal concern for these wastes is that they not be disposed of indiscriminately.

The following table summarizes regulation number, description of the subject matter, decision and location of basis for the decision. The footnotes are numbered from those subsections undergoing the least revision to those undergoing the greatest revision.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

CCR* subsection

Subsection description

Decision

Decision basis

66261.24(a)(1)

Federal Definition of Hazardous Waste1

retain

See below

66261.24(a)(2)

Total Threshold Limit Concentration (TTLC)8

revise

Tab 3: page 7

66261.24(a)(2)

Soluble Threshold Limit Concentration (STLC)9

revise

Tab 3: page 9

66261.24(a)(3)

Acute Toxicity-Oral5

revise

Tab 3: page 10

66261.24(a)(4)

Acute Toxicity-Oral6

revise

Tab 3: page 11

66261.24(a)(5)

Acute Toxicity-Oral7

revise

Tab 3: page 12

66261.24(a)(6)

Fish Bioassay4

revise

Tab 3: page 13

66261.24(a)(7)

Carcinogens3

retain

Tab 3: page 14

66261.24(a)(8)

Experience or Testing ("New Threats")2

retain

Tab 3: page 16

* Citation in Title 22 of the California Code of Regulation (CCR)

1. State RCRA programs must conform to federal law.

2. The Experience or Testing (new threats) subsection of the regulation will be retained as is.

3. Because of its economic importance, TTLCs and SERTs were derived for vinyl chloride. Therefore, vinyl chloride will be removed from the carcinogen list and added to the other two lists. The balance of the listed carcinogens will be retained, and if a waste contains any of these 15 chemicals at concentrations exceeding 10 ppm, they will be classified as hazardous.

4. Fish bioassay will be retained, but the single LC50 threshold for defining hazardous waste will be replaced with an upper and an exit LC50. The basis of this selection is in Appendix 4 of Tab 3.

5. The single oral LD50 value used to determine hazardous from non-hazardous waste will be replaced with an upper and exit LD50. The basis of this selection is described in Appendix 4 of Tab 3.

6. The single dermal LD50 value used to determine hazardous from non-hazardous waste will be replaced with an upper and exit LD50. The basis of this selection is described in Appendix 4 of Tab 3.

7. The algorithm used to determine hazardous from non-hazardous waste based on inhalation toxicity will replaced with two new algorithms. The basis of these algorithms is described in Appendix 4 of Tab 3.

8. See below for a discussion of TTLCs

9. See below for a discussion of SERTs (formerly STLCs)

The changes described in footnotes 1–7 are relatively simple requiring short explanations. The bulk of documentation (Tabs 3–7) pertain to the new approaches proposed for replacing the values for each TTLC and SERT. Each of these criteria will be described in more detail under separate headings.

Total Threshold Limit Concentrations (TTLCs)

Thirty-eight chemicals (or groups of chemicals) each have a numerical TTLC. If the concentration in the waste exceeds the TTLC for any of the 38 chemicals, the waste is categorized as hazardous, otherwise it is unregulated by DTSC. The existing TTLCs were designed to protect human health and the environment from adverse effects resulting from all exposure pathways other than exposure via ground water. The TTLC for each chemical

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

was computed by multiplying the current STLC value by 100 or 10. TTLCs have no counterpart in federal regulation and are deemed important to retain. However, some serious problems exist with the current TTLC values:

Current TTLCs, being simply multiples of the STLCs are not necessarily relevant to non-ground water exposures. They are inflexible, in that they:

  1. Require all wastes be either rigidly regulated or completely unregulated by DTSC
  2. Cannot incorporate advances in technical information
  3. Provide no guidance for decisions on specific waste streams (variances or reclassifications)
  4. Do not provide a defined mechanism for regulating additional chemicals.

Proposed TTLCs were developed using a multi-step, risk-based approach:

  1. Define potentially exposed humans for two waste management situations: 1) wastes managed as special wastes and disposed of in a landfill and 2) wastes unregulated by DTSC.
  2. Identify pathways by which chemical in waste could reach humans for each scenario.
  3. Develop a mathematical model to relate waste concentration to human health risk for each scenario.
  4. Implement these models as spreadsheets to make computation easy and transparent
  5. Using the spreadsheets, compute a human-health-based TTLC for each scenario for each chemical.
  6. For each chemical, determine if human health-based TTLCs protect other species. If not, compute a TTLC based on protection of non-human resources.
  7. Evaluate risk-based TTLCs for science policy considerations.

The risk-based approach to deriving TTLCs addresses the four problems with the current TTLCs. The reader is encouraged to read Appendix 3 of Tab 3 for a general description of the derivation of TTLCs. This section is intended to be a "road map" directing the reader to the spreadsheet descriptions and showing where each fits into the overall process.

Human Health Risk Assessment Scenarios and Models

In order to develop a regulatory threshold, the fate and potential exposure scenarios and pathways for wastes that do not exceed the proposed threshold are evaluated. Thus, the scenarios for the upper TTLCs are associated with managed disposal in a municipal solid waste landfill meeting the specifications in RCRA subtitle D. Similarly, the scenarios for the exit-level TTLCs are associated with use of the waste as a soil amendment. There are many possible exposure scenarios, but DTSC has not identified any plausible scenarios in which exposures to toxic constituents in wastes is likely to exceed the exposures modeled using these scenarios. The scenarios and the models used to evaluate them are described below and summarized in a table following the description.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Upper TTLCs

The toxicologic risk scenarios evaluated for the upper TTLCs include workers at waste handling facilities and residents living adjacent to a waste handling facility. For the workers, a modified Preliminary Endangerment Assessment (PEA) model (see Tab 3, Appendices 3 & 4c) was used. This model was also used to estimate exposure of adjacent residents to inorganic constituents. Exposure of adjacent residents to organic constituents was estimated using the CalTOX model (Tab 3, Appendices 3 & 4a). Non-carcinogenic effects of lead were evaluated for on-site workers using the DTSC Lead Risk Assessment Spreadsheet (see Tab 3, Appendices 3 & 4b).

Exit-level TTLCs

The human health risk scenario evaluated for the lower (exit-level) TTLCs was a resident living on land on which the waste had been applied at the rate of 7000 kg/ha annually for 20 years and thoroughly mixed with the upper 15 cm of soil, such as might occur if the nonhazardous waste were used as a soil amendment and housing were subsequently built on the amended soil. The modified Preliminary Endangerment Assessment (PEA) model (see Tab 3, Appendices 3 & 4c) was used to estimate exposure of these residents to inorganic constituents. Exposure of the residents to organic constituents was estimated using the CalTOX model (see Tab 3, Appendices 3 & 4a). Non-carcinogenic effects of lead were evaluated for all scenarios using the DTSC Lead Risk Assessment Spreadsheet (see Tab 3, Appendices 3 & 4b). Potential effects on non-human receptors were also evaluated in establishing the exit-level TTLCs. The approaches used in this evaluation are described behind Tab 3, Appendices 3 & 4d.

The analyses used for the various scenarios are summarized in the following table:

Criterion

Scenario

Chemicals

Model

Further description

Upper TTLCs

Worker

Organics

modified PEA

Tabs3:Appendix 3 & 4c

Upper TTLCs

Worker

Inorganics

modified PEA

Tab 3:Appendix 3 & 4c

Upper TTLCs

Resident

Organics

CalTOX Landfill

Tab 3:Appendix 3 & 4a

Upper TTLCs

Resident

Inorganics

modified PEA

Tab 3:Appendix 3 & 4c

Upper TTLCs

Worker

Lead

Pb Spreadsheet

Tab 3:Appendix 3 & 4b

Exit-level TTLCs

Resident

Inorganics

modified PEA

Tab 3:Appendix 3 & 4c

Exit-level TTLCs

Resident

Organics

CalTOX Land Conversion

Tab 3:Appendix 3 & 4a

Exit-level TTLCs

Resident

Lead

Pb Spreadsheet

Tab 3:Appendix 3 & 4b

Exit-level TTLCs

Ecological

all

several

Tab 3:Appendix 3 & 4d

After the most protective risk based TTLC criteria were determined, those values were compared against 1) an estimated quantitation limit to determine if that concentration could be measured, and 2) the ambient concentration in soil. The derivation of these science policy values are described in Tabs 5a and 5b, respectively.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Soluble or Extractable Regulatory Thresholds (SERTs)

The existing California waste classification system contains 36 Soluble Threshold Limit Concentrations (STLCs). To evaluate compliance with these criteria, a solid waste is extracted using a procedure called the Waste Extraction Test (WET), and the concentrations of the inorganic chemicals in the extract are compared with their corresponding STLCs. The extract is not normally analyzed for organic chemicals because it is mathematically impossible to exceed the STLC without also exceeding the TTLC. Liquid wastes are analyzed directly, without the extraction. The proposal would replace the WET with the RCRA Toxicity Characteristic Leaching Procedure (TCLP) and replace the 36 STLCs with 35 pairs of SERTs, corresponding to an upper level and an exit level standard for each regulated chemical. Silver would be dropped from the list and there would only be an upper-level SERT for polychlorinated biphenyls (PCBs). The approachs to developing SERTs and the associated extraction methodology are summarized in the table below. The methodology and equations for deriving the proposed SERTs are described in the waste classification concept paper (Tab 3, Appendix 2). The rationale and supporting documants for the proposal to replace the WET with the TCLP is found in Tab 6.

Criterion

Scenario

Pathway

Further description

Upper SERTs

Drinking water

ingestion

Tab 3:Appendix 3

Exit-level SERTs

Drinking water

ingestion

Tab 3:Appendix 3

Exit-level SERTs

Aquatic life

immersion

Tab 3:Appendix 3

Extraction procedure

leaching from a landfill

Tab 3:Appendix 2

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

2. Issues

The Department would like to highlight some key issues for your review: If the panel does not agree with any of the approaches the Department has used, we invite your suggestions for alternative approaches.

TTLC issues

Model Selection
  • Is it appropriate to use a multimedia, multipathway risk assessment model (a variant of CalTOX) to establish concentration limits on organic chemical constituents in various classes of waste? (reference: Tabs 3, Appendix 3 and 4a)
  • Is it appropriate to use a simple exposure model to establish concentration limits on inorganic chemical constituents in various classes of waste? (reference: Tab 3, Appendix 3 and 5c)
  • Is it appropriate to use a lead uptake/blood lead model to establish concentration limits on lead in various classes of waste? (reference: Tab 3, Appendix 3 and 5b)
Scenario Selection
  • Are the waste management worker and the nearby resident scenarios appropriate to represent populations potentially exposed to lower-tier hazardous wastes? The exposures of these populations would be used to establish a 'bright line' to separate wastes which are subject to pre-disposal requirements and must be disposed of in RCRA subtitle C (hazardous waste) landfills from those which are subject to reduced pre-disposal requirements and can be safely disposed of in RCRA subtitle D (MSW) facilities? (reference: Tab 3, Appendix 3) The Department recognizes that some wastes may be disposed of in ways that have greater potential exposure and other wastes may be disposed of in ways that have less potential exposure. Soil is an example of a waste that has a high probability of being disposed of in a way that results in less dilution and therefore potentially greater exposure.

All assessments of carcinogenic risk are based on estimated exposures to a composite person, having characteristics between those of a child and those of an adult. CalTOX also uses this approach for non-carcinogenic effects, while the PEA-based model and the Lead Risk Assessment Spreadsheet assesses exposure to children and adults separately for non-carcinogenic effects (the lowest value is selected for residential exposures while the adult value is used for workers). Which approach is appropriate for carcinogens? For non-carcinogens?

Pathways and Parameters

  • Do the exposure pathways evaluated for workers and residents reasonably represent the exposure potential for these groups of people? (reference: Tabs 4a, 4b, and 4c)
  • In the original submission it was assumed that 30% of a worker's skin is exposed. The 30% figure used in the assessment falls between worst case (shorts, no shirt, with about 60% of the skin exposed) and typical case (long pants, long- or short-sleeved shirt).
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
  • The latter would involve about 13% exposure. The Department was able to obtain only anecdotal information about landfill workers' attire. Is 30% a reasonable mean value for fraction of skin exposed?
  • Although daily cover of active disposal areas is required and only a limited area of a landfill may be active at any given time, no cover was assumed in modeling the landfill. This may be less important for vapors which are expected to escape through gas collection systems regardless of daily cover or capping. With adequate data, a distribution of uncovered area for California landfills and waste piles could theoretically be developed. However, DTSC used conservative modeling parameters partly because of data limitations and also because workers and residents may be exposed to vapors and particles from waste piles, which may not have daily cover.
  • The degree of overestimation of exposure from a landfill source may be considerable for particulate pollutants because their release should be significantly reduced by daily cover or a cap. The degree of overestimation of exposure from a landfill source would likely be much less for vapors, because advective transport is likely to result in vapor emission, usually through a gas collection system, regardless of daily cover or permanent cap. However, only a fraction of the landfill would be producing gases at any given time.
  • No dust dilution was assumed for PEA and Lead spreadsheet modeling, i.e. all respirable particulates are assumed to come from the waste. Monitoring data for California landfills and waste piles were sought, but most existing data are based on complaint follow-ups, and would be highly biased.
  • The U.S. EPA has withdrawn the oral cancer potency factor for beryllium. Treating beryllium as a carcinogen only by the inhalation route would result in about a six-fold increase in the beryllium TTLC. Should beryllium be treated as an oral carcinogen?

Other Issues

  • Is the proposed stepwise approach to ensuring that TTLCs based on human toxicity will protect non-human biota reasonable? (reference: Tab 3, Appendix 3 and 5d)
  • Is the proposed use of two times the estimated quantitation level (EQL) in lieu of a TTLC when the calculated concentration is less than the EQL reasonable? (reference Tab 5a)
  • Is the proposed approach to considering ambient levels of elements and compounds in setting TTLCs appropriate? (reference Tab 5b).

SERT issues

  • SERTs are based on the lowest of (1) health-based concentrations calculated by DTSC, (2) California Maximum Contaminant Levels established by the Department of Health Services, or (3) U.S. EPA Ambient Water Criteria for the protection of aquatic life. Is this paradigm appropriate? (reference: Tab 3, Appendix 2)
  • Is the dilution/attenuation factor of 100 for the SERTs appropriate? (reference: Tab 3, Appendix 2)
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
  • Is the use of a factor to account for the retardation of leakage from the landfill due to the presence of a synthetic liner appropriate? (reference: Tab 3, Appendix 2) Was the liner protection factor calculated appropriately? (reference: Tab 7)
  • The current STLCs and proposed SERTs are based on an assessment of the environmental effects of leachates from solid wastes in a landfill, but apply also to liquid wastes that are not disposed of in a landfill. Should the effects of released liquids be assessed separately? (reference: Tab 3, Appendix 2 & 6)
  • Is laboratory extraction of toxic constituents from solid wastes with municipal solid waste leachates; a reasonable standard against which to compare the performance of laboratory extraction protocols such as the WET, the TCLP, and the SPLP? Is the Department's conclusion that the WET is not a better estimator of leaching potential than the TCLP justified? (reference: Tab 6)
  • We concluded that the extraction by municipal solid waste leachates of elements capable of forming oxyanions was not simulated by the WET or by the TCLP. Is this a reasonable conclusion? (reference Tab 3, Appendix 2 & 6)
  • In the current proposal, ingestion of ground water is the only human exposure pathway evaluated. Does this approach seriously underestimate risk? (reference: Tab 3, Appendix 2)
  • Is the use of the 90th percentile concentration of arsenic in monitored California drinking water supplies as a basis for the arsenic SERT appropriate? (reference Tab 3, Appendix 2)
  • Is the proposed use of two times the estimated quantitation level (EQL) in lieu of a SERT when the calculated concentration is less than the EQL reasonable? (reference tab 5a)

Acute Toxicity Issues

  • Is the Department's proposed approach to setting acute oral, dermal, and inhalation toxicity thresholds reasonable? (reference: Tab 3:Appendix 4)
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

California Environmental Protection Agency Department of Toxic Substances Control

Tab 3: Concept Paper

CALIFORNIA'S NON-RCRA WASTE CLASSIFICATION SYSTEM: Analysis and Proposed Revisions

February 20, 1998

Authors: Jim Carlisle, D.V.M., M.Sc., Ned Butler, Ph.D., D.A.B.T., Kimi Klein, Ph.D., John Christopher, PhD, DABT, Bart Simmons, PhD.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Tab 4: Waste Classification Concept Paper

CALIFORNIA'S NON-RCRA WASTE CLASSIFICATION SYSTEM: Analysis and Proposed Revisions

Description of Issues

The Waste Classification Review

Waste classification review is one of the components of the Regulatory Structure Update project (RSU) of the Department of Toxic Substances Control (DTSC). The objective of the waste classification review is to ensure that California has a scientifically defensible method of classifying waste which protects human health and the environment without unnecessarily hindering sustainable growth and development. This is a multi-step process. The first task was to evaluate the protectiveness of the federal system under the Resource Conservation and Recovery Act (RCRA) with its listed hazardous wastes and the toxicity characteristic. The preliminary conclusion of this task is that the RCRA system is incomplete and does not, by itself, adequately protect human health and the environment in California (see draft concept paper for RSU task D-1). The RCRA system was intended to complement systems for classification and management of wastes in the states.

The Existing California System

The purpose of task D-3 is to evaluate the current California system against the four RSU criteria for change. Those aspects of the California system which remain relevant, appropriate, and scientifically defensible will be retained. Those that fail one or more of the RSU criteria will be modified or dropped.

Recommendation

Develop and adopt a revised California waste classification system establishing two tiers of regulated wastes, but retaining appropriate aspects of the current system.

Circumstances Necessitating a Decision

The finding that the RCRA system was incomplete as a basis for classifying wastes as hazardous in California (RSU task D-1) necessitated a determination of whether the present California waste classification regulations provide an adequate and tenable basis for identifying hazardous wastes in order to protect public health and the environment in California. In the twenty years since the major elements of this system were promulgated, the sciences of toxicology and risk assessment have advanced considerably. It is appropriate at this time to review the California system and update it as necessary.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Existing Statutes or Regulations Related to the Issue

The Hazardous Waste Control Act of 1973 mandated that ''the Department (then the Department of Health Services) shall ''develop and adopt by regulation criteria and guidelines for the identification of hazardous wastes and extremely hazardous wastes" (Section 25141, Health and Safety Code). Section 25159 of the Health and Safety Code authorizes the Department to "adopt and revise when necessary regulations which will allow the State to receive and maintain authorization to administer a State hazardous waste program in lieu of the federal program..." Section 25159.5 of the Health and Safety Code "does not prohibit the Department from adopting standards and regulations which are more stringent or more extensive than federal regulations." Because of the broad authority provided in the original statutes, no new statutes will be required to revise existing regulations pertaining to criteria for identification of hazardous waste.

Existing State regulations describing the characteristic of ignitability are found in 22CCR 66261.21. No changes are proposed in this section because the State characteristic of ignitability is identical to the federal characteristic of ignitability.

Existing State regulations describing the characteristic of corrosivity are found in 22CCR 66261.22. Proposed changes to this section are the subject of RSU task C-11.

Existing State regulations describing the characteristic of reactivity are found in 22CCR 66261.23. No changes are proposed in this section because the State characteristic of reactivity is identical to the federal characteristic of reactivity.

Existing California regulations describing the characteristic of toxicity are found in 22CCR 66261.24. In addition to the RCRA toxicity characteristic, they include tables listing Soluble Threshold Limit Concentrations (STLCs) for 36 compounds. Wastes are analyzed using the Waste Extraction Test (WET, the subject of RSU task D-4), and exhibit the characteristic of toxicity if any of these chemicals are present at extractable concentrations exceeding the STLCs. The STLCs were established to protect ground water and are analogous to, though in some cases different from, the RCRA Toxicity Characteristic (TC) thresholds. RCRA TC thresholds have been established for 40 constituents. There are STLCs for 18 of these constituents. Thirteen of these 18 have the same numerical value. Of the five which have different values, California's standard is higher (less restrictive) for four (chlordane, heptachlor, TCE and trivelent chromium), and lower for one (pentachlorophenol). Since the current test methodology is different, the California standard can be more restrictive, even when the numerical standards are the same.

California regulations in 22CCR 66261.24 include lists of Total Threshold Limit Concentrations (TTLCs) for 38 compounds. The TTLCs were established to protect against human health and environmental impacts resulting from improper management of toxic wastes. Exposure of humans or other animals by ingestion, inhalation, and dermal absorption of toxic compounds was not analyzed directly, but thresholds were established based on a multiple, usually 100, of the STLCs or were established independently based on observed deaths or injuries to humans or livestock.

California regulations also identify wastes as hazardous if they are acutely toxic to mammals or fish, or if they contain any of sixteen listed carcinogenic compounds at a concentration exceeding 10 ppm. Acute oral, dermal, and inhalation toxicity limits were established by

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

multiplying the "highly hazardous" levels recommended by NIOSH (1974) by a safety factor of 100. The fish toxicity threshold is the value used by the federal government to identify commercial substances which may pose a hazard if spilled or discharged into an aquatic environment (40 CFR 116). The carcinogen list is from the Department of Industrial Relations and was produced pursuant to the California Workplace Right to Know Law.

Existing regulations identify as hazardous any waste that has been shown through experience or testing to pose a hazard to human health or the environment for a variety of reasons. The regulations also include a list of presumptively hazardous compounds.

Objectives to be Achieved Through Decision

The proposed action supports the mission of the Department, which is to protect public health and the environment without unnecessarily hindering sustainable growth and development. The recommended changes emphasize (1) consistency with federal standards when possible, (2) maintenance or enhancement of the level of protection when such protection is justified by the waste's toxicity and its likelihood of exposure to humans and non-human biota, (3) reduction of unnecessary costs associated with management of wastes as hazardous when the incremental benefit is minimal, (4) minimization of unnecessary use of limited hazardous waste landfill capacity, and (5) consistency with the four general RSU criteria for decision-making which are:

  1. Are the environmental and public health circumstances and/or lack of federal/state regulatory oversight that led to the establishment of the requirement still in existence?
  2. Are there other regulatory requirements or agencies which adequately cover the concerns addressed by the requirement?
  3. Is the requirement a rational use of environmental protection resources given the potential risks and their probability and significance?
  4. Is there a regulatory alternative that would achieve the desired human health and safety or environmental benefit in a more cost-effective and flexible manner?

Alternatives Available and Recommended Alternative

A. Subsection 66261.24(a)(2)(A&B)

Subsection 66261.24(a)(2)(A&B) contains a list of Total Threshold Limit Concentrations (TTLCs) for specific contaminants in mg/kg waste. If a solid waste contains any of the listed contaminants at a concentration exceeding its TTLC, the waste is a hazardous. With respect to the Total Threshold Limit Concentrations, the options considered were:

1. Repeal the TTLCs in 22CCR Subsection 66261.24 (a)(2)(A&B)

Pro: This alternative would have the advantage of being consistent with RCRA, eliminating the need to perform total extraction on wastes, reducing regulatory burden, and reducing administrative costs.

Con: This alternative would provide for no limits on total concentrations of hazardous constituents in wastes, thereby reducing protectiveness below that mandated by State statutes. The RCRA toxicity characteristic does not address exposure to toxic constituents via media other than ground water. Constituents that do not exceed the federal toxicity

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

characteristic thresholds can contaminate other environmental media such as air, soil, and sediments and thereby harm public health and the environment.

2. Retain the TTLCs 22CCR Subsection 66261.24(a)(2)(A&B) in their current form.

Pro: This alternative would partially protect against harm to public health and the environment through airborne dispersion or particulate dispersion via surface water or by direct exposure to the wastes

Con: The current TTLCs are not based on a consistent multipathway risk analysis. Several are simple multiples of the STLCs. Some do not reflect the most current toxicological data. The all-or-none approach results in over-regulating some wastes and under-regulating others. This alternative would retain a regulatory system more stringent than RCRA.

3. Using a multipathway analytical approach, develop and adopt two tiers of revised TTLCs for constituents for which TTLCs currently exist. Develop TTLCs for additional constituents as permitted by resources and data availability.

Pro: This alternative would address the identified, shortcomings of the RCRA and current California systems.

Con: This alternative would retain a regulatory system more stringent than RCRA. A two-tier system adds complexity to classification of wastes and is expected to increase confusion and need for classification assistance and training. It may increase the volume of wastes disposed in some municipal landfills and could decrease incentives to recycle.

4. Using a multipathway analytical approach, develop and adopt revised TTLCs for constituents for which TTLCs currently exist. Develop TTLCs for additional constituents as permitted by resources and data availability.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain a regulatory system more stringent than RCRA. Since wastes would be either in the DTSC regulatory system or out, without a middle ground for low-risk wastes, some low-risk wastes would be under-regulated, others would be over-regulated.

Recommended Alternative: Alternative 3

Basis of selection:

Criterion 1. The environmental and public health circumstances that led to the regulatory thresholds (TTLCs) in 22CCR Subsection 66261.24(a)(2)(A&B) have changed. In particular, knowledge of toxicological effects, exposure pathways, and the use of mathematical models have advanced considerably since the time the current regulations were promulgated.

Criterion 2. There are no other state lists and no state agencies authorized to create lists of threshold levels of chemicals in wastes for the purpose of defining these wastes as hazardous. The impact of potential exposure by multiple pathways is not considered by the RCRA toxicity characteristic (although multiple pathways were considered in some listings).

Criterion 3. Retaining a list of Total Threshold Limit Concentrations to identify a waste as hazardous is necessary to protect public health and the environment in California. Such a list provides the public with clear guidance in classifying a waste. Revising the TTLCs using up-to-date multimedia, multipathway risk assessment for both humans and ecosystems is necessary to retain scientific credibility. The proposed revised TTLCs meet this criterion by employing methodology that evaluates risks with respect to probability and significance.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Criterion 4. A more cost-effective and flexible regulatory alternative that met the protectiveness standard was not identified. By establishing two subclasses of hazardous wastes using two tiers of TTLCs as toxicity criteria, flexibility in handling and disposing of hazardous waste is integrated into the HWMP. By attaching different requirements to those wastes that exceed the levels, cost-effective management of hazardous waste is achieved.

B. Subsection 66261.24(a)(2)(A&B)

Subsection 66261.24(a)(2)(A&B) contains a list of Soluble Threshold Limit Concentrations (STLCs) expressed in mg/l for specific constituents in liquid waste or the extract from the Waste Extraction Test (WET) performed on a solid waste. DTSC's regulatory program with respect to threats to the waters of the State has RCRA and non-RCRA components. RCRA regulations specify Toxicity Characteristic Regulatory Limits (RLs) for 40 constituents and California has STLCs for 36 compounds. Nineteen compounds have both STLCs and RCRA RLs. With respect to the Soluble Threshold Limit Concentrations, the options considered were:

1. Repeal the STLCs in 22CCR Subsection 66261.24 (a)(2)(A&B)

Pro: This alternative would have the advantage of being consistent with RCRA, reducing regulatory burden, and reducing administrative costs.

Con: This alternative would not provide soluble or extractable concentrations of hazardous constituents in wastes for which there are no RCRA regulatory limits and would not allow for stricter State limits to fully account for carcinogenic effects and/or deficiencies in the TCLP test method for constituents for which there are RCRA regulatory limits.

2. Retain the STLCs in 22CCR Subsection 66261.24(a)(2)(A&B) in their current form.

Pro: This alternative would partially protect against harm to public health and the environment from exposure to soluble or extractible concentrations of hazardous constituents in wastes for which there are no RCRA regulatory levels.

Con: This alternative would not allow for updating the STLCs to reflect the most current toxicology data and to account for deficiencies in the test methodology. The all-or-none approach results in over-regulating some wastes and under-regulating others. This alternative would retain inconsistency with RCRA and other states.

3. Revise 22CCR Subsection 66261.24(a)(2)(A&B) to establish two tiers of Soluble or Extractible Regulatory Thresholds (SERTs), which would replace the current STLCs. Develop SERTs for additional constituents as permitted by resources and data availability.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain inconsistency with RCRA and other states.

4. Revise 22CCR Subsection 66261.24(a)(2)(A&B) to establish risk-based STLCs. Develop STLCs for additional constituents as permitted by resources and data availability.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain inconsistency with RCRA and other states. Since wastes would be either in the DTSC regulatory system or out, without a middle ground for low-risk wastes, some low-risk wastes would be under-regulated, others would be over-regulated.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Recommended Alternative: Alternative 3

Basis of selection:

Criterion 1. The circumstances that led to the regulatory thresholds (STLCs) in 22CCR Subsection 66261.24(a)(2)(A&B) have changed. In particular knowledge of toxicological effects on humans and aquatic ecosystems have advanced considerably since the time the current regulations were promulgated. A list of Soluble or Extractible Regulatory Thresholds (SERTs, formerly Soluble Threshold Limit Concentrations, STLCs) for specific chemicals as part of a comprehensive methodology to classify wastes continues to be necessary to protect the environmental and public health in California, because such a list provides the public with clear guidance regarding the categorization of a waste as hazardous. Revising the SERTs using the most recent toxicological data to evaluate the impacts of these chemicals on aquatic systems and on human health will maintain the scientific credibility of these standards.

Criterion 2. There are no other state lists and no state agencies authorized to create lists of threshold levels of chemicals in wastes for the purpose of defining those wastes as hazardous. Protection of the waters of the State requires a coordinated approach between DTSC and the State Water Resources Control Board and the Regional Water Quality Control Boards. These Boards regulate discharge of wastes to land. DTSC currently classifies wastes as hazardous or extremely hazardous. Land disposal of hazardous wastes generally must be in a Class 1 landfill. Wastes that are not classified by DTSC as hazardous may be classified by the Boards as "designated", "non-hazardous solid", or "inert". These classifications require that land disposal be in at least class II, class III, or unclassified landfills, respectively. DTSC's hazardous waste management program and those of the Water Boards must mesh in a seamless manner. DTSC will facilitate this by making it clear that wastes that are not regulated by DTSC may be subject to other regulatory requirements.

Criterion 3. The proposed revised SERTs are derived using methodology that evaluates risks in regard to probability and significance, and, therefore, meets this criterion.

Criterion 4. A more cost-effective and flexible regulatory alternative that met the protectiveness standard was not identified. By establishing two subclasses of hazardous wastes using two tiers of SERTs as toxicity criteria, flexibility in handling and disposing of hazardous waste is integrated into the HWMP. By attaching different requirements to those wastes that exceed the levels, cost-effective management of hazardous waste is achieved.

C. Subsection 66261.24 (a)(3)

Subsection 66261.24 (a)(3) contains a lower limit on the acute oral median lethal dose (LD50, the dose of the waste that is fatal to half of the animals exposed) of 5000 mg/kg. Existing statute lowers that threshold to 2500 mg/kg. With respect to the acute oral LD50, the options considered were:

1. Repeal 22CCR Subsection 66261.24 (a)(3)

Pro: This alternative would have to advantage of being consistent with RCRA, reducing regulatory burden, and reducing administration costs.

Con: This alternative would not permit identification of wastes as hazardous based on their acute oral toxicity. This would reduce protectiveness below that mandated by state statutes because there may be waste constituents or combinations of waste constituents that may be acutely toxic for which chronic toxicity benchmarks have not been established.

2. Retain 22CCR Subsection 66261.24(a)(3) in its current form.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Pro: This alternative would protect against harm to public health from oral exposure to acutely toxic constituents in wastes for which there are no established chronic toxicity benchmarks.

Con: This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others, and would retain a classification that differs from the federal system and other states' systems.

3. Develop and adopt a revised 22CCR Subsection 66261.24(a)(3) establishing two acute oral toxicity limits corresponding to the two tiers of regulated wastes.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain inconsistency with RCRA and other states.

4. Develop and adopt a revised 22CCR Subsection 66261.24(a)(3) establishing a risk-based acute oral toxicity limit.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others, and would retain a classification that differs from the federal system and other states' systems.

Recommended Alternative: Alternative 3

Basis of selection:

See below under Subsection 66261.24 (a) (5).

D. Subsection 66261.24 (a)(4)

E. Subsection 66261.24 (a)(4) contains a lower limit on the acute dermal median lethal dose (dermal LD50) of 4300 mg/kg. With respect to the acute dermal LD50, the options considered were:

1. Repeal 22CCR Subsection 66261.24 (a)(4)

Pro: This alternative would have the advantage of being consistent with RCRA, reducing regulatory burden, and reducing administrative costs.

Con: This alternative would not permit identification of wastes as hazardous based on their acute dermal toxicity. This would reduce protectiveness below that mandated by state statutes because there may be waste constituents or combinations of waste constituents that may be acutely toxic for which chronic toxicity benchmarks have not been established.

2. Retain 22CCR Subsection 66261.24(a)(4) in its current form.

Pro: This alternative would protect against harm to public health from dermal exposure to acutely toxic constituents in wastes for which there are no established chronic toxicity benchmarks. It is important to separately evaluate dermal toxicity because chemicals that are well absorbed through the skin may present unique hazards.

Con: This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others. This alternative would retain inconsistency with RCRA and other states.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

3. Develop and adopt a revised 22CCR Subsection 68261.24(a)(4) establishing two acute dermal LD50 limits corresponding to the two tiers of regulated wastes.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain inconsistency with RCRA and other states.

4. Develop and adopt a revised 22CCR Subsection 68261.24(a)(4) establishing a risk-based acute oral toxicity limit.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others, and would retain a classification that differs from the federal system and other states' systems.

Recommended Alternative: Alternative 3

Basis for Selection:

See below under Subsection 66261.24 (a)(5).

E. Subsection 66261.24 (a)(5)

Subsection 66261.24 (a)(5) contains a lower limit on the acute inhalation median lethal concentration (LC50, the concentration of the waste that is fatal to half of the animals exposed) of 10,000 ppm as a gas or vapor. With respect to the acute inhalation LC50, the options considered were:

1. Repeal 22CCR Subsection 66261.24 (a)(5)

Pro: This alternative would have the advantage of being consistent with RCRA, reducing regulatory burden, and reducing administrative costs.

Con: This alternative would not permit identification of wastes hazardous based on their acute inhalation toxicity. This would reduce protectiveness below that mandated by state statutes because there may be waste constituents or combinations of waste constituents that may be acutely toxic for which chronic toxicity benchmarks have not been established.

2. Retain 22CCR Subsection 86261.24(a)(5) in its current form.

Pro: This alternative would protect against harm to public health from inhalation exposure to acutely toxic constituents in wastes for which them are no established chronic toxicity benchmarks.

Con: This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others. This alternative would retain inconsistency with RCRA and other states.

3. Develop and adopt a revised 22CCR Subsection 66261.24(a)(5) establishing two acute inhalation LC50 limits corresponding to the two tiers of regulated wastes, allowing calculated head-space vapor concentrations, and adjusting for percent respirable particles.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Con: This alternative would retain inconsistency with RCRA and other states and would add complexity to the regulations.

4. Develop and adopt a revised 22CCR Subsection 66261.24(a)(5) establishing acute inhalation LC50 limits, allowing calculated head-space vapor concentrations, and adjusting for percent respirable particles.

Pro: This alternative would address the identified shortcomings of the RCRA and current California systems.

Con: This alternative would retain inconsistency with RCRA and other states and would add complexity to the regulations. It would also continue the all-or-none approach which results in over-regulating some wastes and under-regulating others

Recommended Alternative: Alternative 3

Basis for selection of alternatives presented for subsections 66261.24 (a) (3), (4), and (5):

Criterion 1. The circumstances leading to the adoption of acute toxicity criteria have not changed. Consideration of acute oral, dermal, and inhalation toxicity remain necessary in classifying waste in order to protect the public health. Acute toxicity is still not considered in the RCRA Toxicity Characteristic and, thus, represents a gap in federal regulatory oversight.

Criterion 2. There are no other state lists and no state agencies authorized to create criteria for acute toxicity of chemicals in wastes for the purpose of defining those wastes as hazardous. The RCRA program does not include acute toxicity limits in the Toxicity Characteristic.

Criterion 3. Specific waste constituents or combinations of waste constituents may be acutely toxic if accidently ingested, spilled on the skin, or inhaled, and may not have chronic toxicity benchmarks. It is reasonable to use this regulatory framework to protect human health from such exposure.

Criterion 4. A more cost-effective and flexible alternative to the proposal has not been identified. By establishing two subclasses of hazardous wastes using two tiers of acute lethal dose (LD50) or acute lethal concentration (LC50) as toxicity criteria, flexibility in handling and disposing of hazardous waste based on relative toxicity is integrated into the HWMP. By attaching different requirements to those wastes that exceed the levels, cost-effective management of hazardous waste is achieved.

F. Subsection 66261.24 (a)(6)

Subsection 66261.24 (a)(6) contains a lower limit on the 96-hour aqueous median lethal concentration (LC50, the concentration of the waste that is fatal to half of the fish exposed) of 500 mg/l. With respect to the aquatic LC50, the options considered were:

1. Repeal 22CCR Subsection 66261.24(a)(6)

Pro: This alternative would have the advantage of being consistent with RCRA, reducing regulatory burden, and reducing administrative costs.

Con: This alternative would not permit identification of wastes as hazardous based on their toxicity to fish. This would reduce protectiveness below that mandated by state statutes because there may be waste constituents or combinations of waste constituents that may be acutely toxic to fish for which chronic toxicity benchmarks have not been established.

2. Retain 22CCR Subsection 66261.24(a)(6) in its current form.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Pro: This alternative would protect against harm to aquatic organisms from exposure to substances which are acutely toxic to fish but are not hazardous by any other criterion.

Con: This alternate would retain inconsistency with RCRA and other states and could over-regulate some wastes.

3. Develop and adopt a revised 22CCR Subsection 66261.24(a)(6) establishing two acute aquatic LC50 limits corresponding to the two tiers of regulated wastes.

Pro: This alternative would be consistent with the proposed two-tier standards for the other toxicity criteria.

Con: An upper tier of fish LC50 limits (creating an upper tier of hazardous wastes based on fish toxicity) would over-regulate some wastes because Class 1 containment is not necessary to mitigate the hazard to fish posed by direct exposure. This alternative would retain inconsistency with RCRA and other states.

4. Retain 22CCR Subsection 66261.24(a)(6) but use the fish bioassay results only to bring wastes into the lower tier of hazardous wastes.

Pro: This alternative would protect against harm to aquatic organisms from exposure to substances which are acutely toxic to fish but are not hazardous by any other criterion without imposing unnecessarily stringent requirements on some wastes. Class 1 containment is not necessary to mitigate the hazard to fish posed by direct exposure.

Con: This alternative would retain inconsistency with RCRA and other states.

Recommended Alternative: Alternative 4

Basis for Selection:

Criterion 1. The circumstances leading to the adoption of the aquatic toxicity criterion have not changed. The people of California still expect regulatory agencies to protect the environment. Aquatic toxicity is generally not covered by the RCRA program and, thus, represents a lack of federal oversight.

Criterion 2. The State Water Resources Control Board has regulatory oversight over waters of the State. However, the Board does not have the authority to define wastes as hazardous. Without that ability, the the Board may not have sufficient authority to regulate wastes in a manner that fully protects aquatic resources.

Criterion 3. Protecting aquatic life by requiring the performance of a fish bioassay is a rational use of resources, as this is the only test required that directly measures the impact of a waste constituent on aquatic life, and it is the only test that directly measures the integrated toxicity of a waste as a whole.

Criterion 4. The requirement that wastes failing this test need only be managed as special wastes provides the regulated public with the most cost-effective alternative and maximum flexibility, given the mandate of the Department to protect the environment.

G. Subsection 66261.24 (a)(7)

Subsection 68261.24 (a)(7) contains a list of sixteen carcinogenic compounds which, if present at more than 10 ppm in the waste, render it hazardous. The options for this subsection were:

1. Repeal 22CCR Subsection 66261.24(a)(7)

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Pro: This alternative would have the advantage of being consistent with RCRA, reducing regulatory burden, and reducing administrative costs. Most of the listed carcinogens are RCRA-listed hazardous wastes.

Con: This alternative could, by itself result in partially deregulating several carcinogens. RCRA-listed hazardous wastes are only hazardous to the extent that they meet the RCRA definitions.

2. Retain 22CCR Subsection 66261.24(a)(7) in its current form.

Pro: This alternative would partially protect against harm to public health from exposure to the listed carcinogens.

Con: This alternative would retain the single threshold which does not recognize the varying carcinogenic potency of the listed compounds. This alternative would continue the all-or-none approach which results in over-regulating some wastes and under-regulating others, and would retain inconsistency with RCRA and other states.

3. Repeal 22CCR Subsection 66261.24(a)(7). Add vinyl chloride to the TTLC and SERT lists and add the balance of the listed carcinogens to Appendix X to section 66261. Classify future identified carcinogens via TTLCs and SERTs.

Pro: This alternative would provide for a consistent methodology for assessing risk of carcinogenic effects and with the proposed two-tier standards for the other toxicity criteria and would be consistent with the proposed two-tier standards for the other toxicity criteria. There is no scientific reasons to consider carcinogens as a separate class of hazardous wastes. This alternative would allow generators of the formerly listed carcinogens to demonstrate that their wastes are not hazardous. Several of the proposed TTLCs are based on carcinogenicity.

Con: This alternative would retain inconsistency with RCRA and other states and would reduce the control over the fifteen chemicals moved to Appendix X, because they would no longer have regulatory thresholds.

4. Retain 22CCR Subsection 66261.24(a)(7). Remove vinyl chloride from the carcinogen list, but add it to the TTLC and SERT lists. Classify future identified carcinogens via TTLCs and SERTs.

Pro: This alternative would provide risk-based thresholds for vinyl chloride, while not decreasing protection for the other listed carcinogens.

Con: This alternative would retain inconsistency with RCRA and other states and would retain the non-risk-based thresholds for fifteen carcinogens.

Recommended Alternative: Alternative 4

Basis for selection:

Criterion 1. The compounds listed in existing regulation were originally identified as carcinogenic by the Occupational safety and Health Administration (OSHA) in 1977. Since that time, much research has been done on carcinogenic compounds, many additional compounds have been found to be carcinogenic, and the majority of compounds on the list are no longer in general commerce. Consideration of carcinogenicity is now an integral component of assessing risk of chronic exposure to chemicals. Public health circumstances have not changed with regard to the requirement of regulatory agencies to protect against undue exposure to carcinogenic compounds. Therefore, although the current list is very much out-of-date, consideration of carcinogenicity in the evaluation of wastes is still necessary.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Criterion 2. Although many of the chemicals on this current list are listed on the RCRA U or P list, they may not be captured as RCRA-listed hazardous wastes because of definitional limitations.

Criterion 3. Since research has shown that chemicals exhibit varying carcinogenic potency, regulating sever carcinogenic compound at a single concentration limit would not result in equal protection from contracting cancer. The risk assessment methods used to SERT and TTLC values include carcinogenicity, thus, carcinogenic chemicals would be evaluated and listed in Subsection 66261.24 (a)(2). Vinyl chloride will be added to the SERT and TTLC list on the basis of its carcinogenicity.

Criterion 4. Repealing this list may be cost-effective, but may not meet DTSC's statutory mandates.

H. Subsection 66261.24 (a)(8)

Subsection 66261.24 (a)(8) identifies as hazardous any waste that has been shown through experience or testing to pose a hazard to human health or the environment for any of several reasons. With respect to this so-called new threats category, the options considered were:

1. Repeal 22CCR Subsection 66261.24(a)(8)

Pro: This alternative would have the advantage of being consistent with RCRA, (the Federal system lacks the ability to administratively identify a waste as hazardous on the basis of new knowledge), potentially reducing regulatory burden, and reducing administrative costs.

Con: This alternative would remove DTSC's ability administratively identify a waste as hazardous on the basis of new knowledge. Without this ability, continued human exposure or environmental harm could occur while DTSC goes through the rulemaking process to regulate a new or newly identified hazard.

2. Retain 22CCR Subsection 66261.24(a)(8) in its current form.

Pro: This alternative would allow the Department to administratively identify a waste as hazardous on the basis of new knowledge. This ability is important in order to prevent continued human exposure or environmental harm while DTSC goes through the rulemaking process to regulate a new or newly identified hazard.

Con: This alternative could potentially increase regulatory burden and administrative costs.

3. Revise 22CCR Subsection 66261.24(a)(8).

Pro: None identified

Con: No needed revisions to this section were identified.

Recommended Alternative: Alternative 2

Basis for Selection:

Criterion 1. The circumstances leading to the adoption of the ''new threats'' criterion have not changed. Protection of the environment and public health requires that this toxicity characteristic be retained to protect against undue exposure to future wastes that are found to be hazardous to public health or the environment.

Criterion 2. There are no other state agencies authorized to create criteria to classify chemicals in wastes for the purpose of defining those wastes as hazardous. The RCRA program does not include carcinogenicity, toxicity, bioaccumulative or persistent properties as part of Itte toxicity characteristic, and cannot administratively list wastes as hazardous.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Criterion 3. The subsection represents a rational use of resources because of its general wording that recognizes that future experience and testing will likely uncover chemicals that should be identified as hazardous wastes.

Criterion 4. The subsection provides flexibility to the Department in identifying specific wastes as hazardous.

Implementation of the Recommended Alternatives

A. Modifications to Section 66261.24(a)(2): SERTs

DTSC proposes to replace the STLCs with two-tiered regulatory limits called Soluble or Extractible Regulatory Thresholds (SERTs). Wastes containing extractible concentrations of regulated constituents exceeding the upper SERT would be classified as non-RCRA hazardous wastes. Wastes containing extractible concentrations of regulated constituents exceeding only the lower (exit-level) SERT would be classified as Special Wastes, assuming that the waste is not hazardous by any other criterion. Special Wastes are a subset of hazardous wastes to which reduced regulatory requirements would apply. Table 1 presents proposed upper and lower SERTs along with current STLCs. If the SERT is >1/20 of the TTLC, the SERT applies only to liquid wastes. Derivation of proposed SERTs is presented in Appendix 2.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Table 1: Proposed SERTs vs. current standards (mg/l)

 

Proposed

based on

Proposed lower

based on

current

current RCRA

Aldrin

0.4

EQLe

0.006

TTLC

0.14

none

Chlordane

0.008

AWQCa

0.0007

EQLe

0.25

0.03

DDT & metabolites

0.005

EQLe

0.0005

EQLe

0.1

none

2.4-D

100

MCLc

7

MCLc

10

10

Dieldrin

0.009

EQLe

0.0009

EQLe

0.8

none

Endrin

0.008

EQLe

0.0008

EQLe

0.02

0.02

Heptachlor

0.008

EQLe

0.0008

EQLe

0.47

0.008

Kepone

0.4

HBLb

0.04

EQLe

2.1

none

Lindane

0.1

AWQCa

0.008

AWQCa

0.4

0.4

Methoxchlor

0.05

AWQCa

0.003

AWQCa

10

10

Mirex

0.003

EQLe

0.0003

EQLe

2.1

none

Pentachlorophenol

2

MCLc

0.1

MCLc

1.7

100

PCB

5d

existing

noned

 

5

none

PCDD/PCDF

none

 

none

 

0.001

none

Toxaphene

0.02

EQLe

0.002

EQLe

0.5

0.5

TCE

9

MCLc

0.5

MCLc

204

0.5

2.4.5-TP (Silvex)

90

MCLc

5

MCLc

1

1

vinyl chloride

0.9

MCLc

0.05

MCLc

none

0.2

organic lead

20

EQLe

2

EQLe

 

 

Antimonyh

10

EQLe

1

EQLe

15

none

Arsenich

59

HBLb

1

ambient

5

5

Barium

2000

MCLc

100

MCLc

100

100

Beryllium

1

EQLe

0.1

EQLe

0.75

none

Cadmium

2

AWQCa

0.1

AWQCa

1

1

Hexavalent chromium

20

HBLb

0.2

HBLb

5

none

Total chromium

90

MCLc

5

MCLc

560

5

Cobalt

4000

HBLb

200

HBLb

80

none

Copper

20

AWQCa

1

AWQCa

25

none

Fluoride

4000

HBLb

200

HBLb

180

none

Mercury

0.04

EQLe

0.004

EQLe

0.2

0.2

Molybdenumh

300

HBLb

10

HBLb

350

none

Nickel

200

MCLc

10

MCLc

20

none

Lead (inorganic)

5

AWQCa

0.3

AWQCa

5

5

Seleniumh

9

AWQCa

0.5

AWQCa

1

1

Thallium

4

MCL

0.2

MCL

7

none

Vanadiumh

500

HBLb

20

HBLb

24

none

Zinc

200

AWQCa

10

AWQCa

250

none

a. Based on federal Ambient Water Quality Criteria @ 100 ppm hardness or a pH of 6.5 and the longest available exposure, and a dilution/attenuation factor of 100 (the initial value of 0.0002 for toxaphene was raised to the PQL).

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

b. DTSC health-based concentration multiplied by 100

c. The California Maximum Contaminant Level (MCL) multiplied by 100

d. No now standard is proposed for PCBs

e. Based on the estimated quantification limit.

f. If the proposed value exceeds the RCRA RL, then the proposed value would apply only to federally exempt wastes.

g. The calculated value was 4, which is not sufficiently different from the current STLC to warrent a change.

h. Because of limitations in the TCLP, SERTs for this chemical apply only to liquid wastes

B. Modifications to Section 66261.24(a)(2): TTLCs

California currently has Total Threshold Limit Concentrations (TTLCs) for 38 substances. The Department proposes to replace existing TTLCs with two revised TTLC values - an upper and a lower (exit-level) TTLC - for each of 34 constituents. Silver is droped from the list because it is not believed to represent significant threat. The current TTLC for PCBs is being retained pending anticipated changes in analytical methods and toxicological benchmarks. No upper TTLCs are proposed for zinc and total chromium because the calculated values for these standards are at or near 1 million ppm. Proposed TTLCs, along with the existing TTLCs are shown in Table 2:

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Table 2: proposed TTLCs and Current TTLCs (mg/kg)

Chemical

Upper TTLCa

Basisd

Lower TTLCa

Basisd

Existing TTLC

Aldrin

0.7

EQL

0.05

EQL

1.4

Chlordane

1

HBL

0.06

HBL

2.5

DDT & congeners

1

HBL

0.3

HBL

1

2.4-D

1500

HBL

nonef

 

100

Dieldrin

0.9

EQL

0.06

EQL

8

PCDD/PCDF

0.0002

ambient

nonef

 

.01

Endrin

70

HBL

0.1

HBL

0.2

Heptachlor

0.8

EQL

nonef

 

4.7

Kepone

40

EQL

3

EQL

21

Lead (organic)

100

EQL

10

EQL

13

Lindane

30

HBL

5

HBL

4

Methoxychlor

2000

HBL

100

HBL

100

Mirex

0.9

HBL

0.04

HBL

21

Pentachlorophenol

500

HBL

nonef

 

17

Polychlorinated biphenyls (PCBs)

50

existingb

none

 

50

Tricholoethylene(TCE)

20

HBL

nonef

 

2040

Toxaphene

2

EQL

0.1

EQL

10

Silvex

1000

HBL

nonef

 

5

Vinyl chloride

1

EQL

0.2

EQL

.01

Antimony

700

HBL

nonef

 

500

Arsenic

40

HBL

nonef

 

500

Asbestos

none

na

1% (by wt.)

existingb

1% (by wt.)

Barium (excluding barite)

100,000

HBL

nonef

 

10,000

Beryllium

20

HBL

nonef

 

75

Cadmium

150

HBL

60

HBL

100

Hexavalent Chromium

5

HBL

nonef

 

500

Total Chromium

noneh

HBL

noneh

HBL

2500

Cobalt

15,000

HBL

nonef

 

8000

Copper

70,000

HBL

nonef

 

2,500

Fluoride

100,000

HBL

nonef

 

18,000

Lead

6000

HBL

1000

HBL

1,000

Mercuryc

500

HBL

7

ambient

20

Molybdenum

9000

HBL

nonef

 

3,500

Nickel

3000

HBL

nonef

 

2,000

Selenium

30

STLC

none

 

100

Silver

none (see text)

 

none (see text)

 

500

Thallium

150

HBL

nonef

 

700

Vanadium

1000

STLC

none

 

2,400

Zinc

noneg

na

noneg

na

5,000

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

b. The TTLCs for asbestos and PCBs were not reevaluated and will remain unchanged.

c. Wastes containing elemental mercury at any concentration are hazardous.

d. EQL = estimated quantitation limit; HBL = health-based limit; ambient - see text

f. The calculated lower TTLC was not significantly lower than the upper TTLC see text

g. No regulatory limit proposed - calculated value is at least 400,000 mg/kg.

Under the proposal, as under current regulation, wastes would be analyzed for the chemical constituents for which TTLC values exist. As in current regulation, measured total concentrations in a waste would be compared with listed TTLC values to determine how to classify the waste. If the total concentration measured in the waste exceeds the upper TTLC for any of the chemicals in the table, then the waste is a fully regulated hazardous waste. If the measured concentration in the waste is below the lower TTLC for all of the chemicals in those tables and passes all the other criteria, then the waste is not subject to regulation by DTSC. If the concentration of any constituent measured in the waste is between the upper and lower TTLC values, and it is not fully hazardous by any other criterion, then the waste will be classified as a California special waste. An explanation of the derivation of the proposed TTLCs is in Appendix 3. Appendix 1 contains brief toxicological profiles and basis for regulatory limits for the constituents for which DTSC is developing regulatory thresholds.

Regulation of Wastes Containing Elemental Metals

The Department currently only regulates elemental metals in wastes "...if the substances are in a friable, powdered, or finely divided state [22CCR, §66261.24(a)(2)(A)]." The current working definition for powdered or finely divided is material which passes a 100 micron sieve. Since the primary route of exposure is inhalation, the Department is considering only regulating elemental metals which have a particle size less than 10 microns. A sonic sifting method is available to measure particle size down to 5 microns, and a test of a metal-containing waste showed that the method can be used effectively on actual industrial wastes. The concentration of regulated metals would be calculated by the following formula:

regulated metal in waste (mg/kg) = metals conc in sub 10 micron fraction (mg/kg) * wt of sub 10-micron fraction (kg)/Total wt of sample (kg)

Wastes containing elemental mercury are hazardous regardless of concentration.

C. Modifications to Section 66261.24(a)(3): Acute Oral LD50

It is important to retain the acute toxicity criterion to protect humans against the most immediate threats of illness or injury. Furthermore, acute toxicity is the only method within the California waste classification system of identifying toxic effects on humans of waste constituents which are not on the list of persistent and bioaccumulative compounds. DTSC recommends the adoption of two-tiered acute toxicity criteria to ensure that highly toxic substances are managed so as to avoid exposures at toxic levels while not over-regulating chemicals of moderate acute toxicity. DTSC has developed recommended acute toxicity thresholds for hazardous wastes and special wastes. The oral LD50 of a waste may be determined in a closing study with laboratory animals or may be calculated from published LD50 values of the individual components of the waste using the following formula:

LD50 (waste) = 100/(weight % Ca/LD50 Ca + weight % Cb/LD50 Cb ... + weight % Cn/LD50 Cn)

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

where Cn represents the nth acutely toxic chemical in the wastes. Hazardous wastes would include wastes with a calculated or experimentally determined oral LD50 less than 30 mg/kg. Non-hazardous wastes would include those with an oral LD50 exceeding 500 mg/kg. Special wastes would include wastes with oral LD50s between 30 and 500 mg/kg. Derivation of these values is in Appendix 4.

D. Modifications to Section 66261.24(a)(4): Acute Dermal LD50

Hazardous wastes would include wastes with a calculated or experimentally determined dermal LD50 less than 5500 mg/kg. Non-hazardous wastes would include those with a dermal LD50 exceeding 7400 mg/kg. Special wastes would include wastes with dermal LD50s between 5500 and 7400 mg/kg. Derivation of these values is on page 45 in Appendix D. The formula for calculating the dermal LD50 of a waste is:

LD50 (waste) = 100/(weight % Ca/LD50 Ca + weight % Cb/LD50 Cb ... + weight % Cn/LD50 Cn) where Cn represents the nth acutely toxic chemical in the waste.

E. Modifications to Section 66261.24(a)(5): Acute Inhalation LC50

Under the proposed classification system, wastes would need to be evaluated for risk of acute toxic effects from inhalation exposures to both volatiles and particulates. The highest category determines the classification of the waste.

Volatiles: In order to account for both a chemical's acute inhalation toxicity and its tendency to vaporize, classification of a waste containing volatile constituents would be based on the ratio of each constituent chemical's vapor pressure (in ppm @ 25° C) to its inhalation LC50 (in ppm). If this ratio exceeds 0.1, the waste containing the chemical would be a special waste. If this ratio exceeds 1, the waste containing the chemical would be a hazardous waste. These ratios must be summed for wastes with multiple volatile chemicals, i.e. Σ(VP/LC50) > 0.1 yields a special waste classification and Σ(VP/LC50) > 1 yields a hazardous classification. In order to calculate this ratio, vapor pressure in mm Hg is converted to vapor pressure in atmospheres by dividing by 760. This, in turn is converted to ppm by multiplying by 1 million.

Particulates: Classification of a waste based on its particulate constituents would be based on the respirable fraction of the waste (the fraction with a particle size less than 10 microns) times the sum of the ratios of each chemical's concentration (in mg/kg) in the respirable fraction divided by its inhalation LC50 (in mg/m3). This C/LC50 ratio accounts for the tendency of the chemical to be suspended in the air and for its acute toxicity by inhalation. The table below is used to classify the waste:

Vapor pressure/LC50 ratio sum

Classification

Concentration/LC50 sum

VP/LC < 0.1

Non-hazardous waste

C/LC50 = < 105

0.1< VP/LC < 1

special Waste

not applicable

VP/LC > 1

Hazardous Waste

C/LC50 > 105

Derivation of these values is in Appendix D, page 45.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
F. Modifications to Section 66261.24(a)(6): Aquatic Toxicity

The Department recommends retaining the fish bioassay and the current exit threshold. The fish bioassay is important because it is the only method within the California waste classification system of identifying ecotoxic properties of waste constituents which are not on the list of persistant and bioaccumulative compounds and it is the only method for evaluating the integrated toxic effects of multiple constituents of a waste. Wastes with aquatic LC50s below 500 mg/l, but above 30 mg/l would be classified as special wastes. With concurrence from the Regional Water Quality Control Board, special wastes could be disposed of in lined municipal solid waste landfills meeting current RCRA Subtitle D requirements for new landfills. Wastes with aquatic LC50s below 30 mg/l would be classified as hazardous wastes and would require disposal in Class 1 landfills.

G. Modifications to Section 66261.24(a)(7): Listed Carcinogens

The Department recommends that vinyl chloride be removed from the carcinogenicity section, since it is being added to the TTLC and SERT lists.

H. Modifications to Section 66261.24(a)(8): New Threats

The Department recommends that this criterion be retained. As industrial processes and consumer products evolve, there will be new chemicals in commerce and new opportunities for exposures to humans or non-human biota. Without the ability to identify as hazardous those wastes which have been shown to be toxic by testing or experience, the time required to promulgate new regulation may prevent the Department from acting quickly to remedy a situation arising from a new chemical, a new type of exposure, or new knowledge.

I. Classification of wastes under the proposed regulatory structure

Figure 1 on the following page is a diagram of the proposed non-RCRA classification structure, excluding sections 66261.24(a)(7) and (a)(8). Note: Nothing in this document shall be construed to amend or repeal current regulations. All current regulations remain in effect unless and until DTSC has completed rulemaking and a new requirement is formally adopted.

Reclassifications and Variances

The TTLCs, SERTs, and acute toxicity thresholds are rigid criteria applied to all wastes regardless of their location or physical characteristics. Not all wastes containing a concentration of chemical exceeding one or more of these criteria are likely to adversely affect human health or the environment. The physical characteristics of the waste and its management greatly influence the potential hazard. The Department is called on to reclassify wastes or grant variances based on physical characteristics and/or management practices. Defining a process for computing a revised set of TTLCs and SERTs based on multimedia risk assessment would establish a logical basis for reclassifying wastes using applicant-supplied waste-specific or site-specific parameters in the model. DTSC proposes to use the paradigms described herein as a conceptual basis for analyzing mitigating properties or circumstances in review of applications for variances and reclassifications.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Appendix 1: Regulated chemicals

Organic Chemicals

Aldrin is a chlorinated insecticide that is no longer produced in or imported into the United States. It is closely related to dieldrin chemically and is readily converted to dieldrin in the environment. It is dieldrin which bioaccumulates in the environment. It is relatively insoluble in water and persists in soil. Aldrin is well absorbed through the skin and is acutely toxic to mammals, fish, and birds. The Cal/EPA oral and inhalation cancer potency factor is 17 (mg/kg-day).-1. Aldrin also causes non-cancer liver effects at very low doses equivalent to the 10-5 cancer risk level.

Chlordane is a chlorinated insecticide that is no longer used in the United States because of its adverse health effects and persistence in the environment. However, it is still manufactured for export. It has been found in water, soil, and air as it was widely used as a termiticide. Chlordane is absorbed through the skin and mucous membranes and is bioaccumulated in human body fat. Chlordane is also bioaccumulated in fish, birds, and mammals. Chlordane is highly toxic to aquatic organisms. The Cal/EPA oral and inhalation cancer potency factor is 1.2 (mg/kg-day)-1, based on liver tumors in laboratory animals. However, chlordane causes non-cancer liver effects at very low doses and the TTLCs are determined by these effects because they occur at lower doses than the liver tumors. It is also important to realize that non-cancer effects are based on a maximum annual concentrations rather than a time-weighed average over the exposure duration. The maximum dose occurs via the breast milk pathway during the first year of life.

DDT (dichloro diphenyl trichloroethane) is an insecticide that has been banned for agricultural uses in the United States since 1972 because of its environmental persistence, accumulation in the food chain, interference with avian reproduction, and carcinogenicity in laboratory animals. It is insoluble in water and binds tightly to soil particles. DDT is moderately acutely toxic to mammals, fish, and birds. The Cal/EPA oral and inhalation cancer potency factor is 0.34 (mg/kg-day)-1. DDT is transformed in the environment to DDE and DDD. The toxicity and movement of these three compounds is similar, though not identical.

2,4-D (2,4-Dichlorophenoxyacetic Acid) is a chlorinated organic acid herbicide that does not persist in soil, but can move readily through soil to groundwater. It is nontoxic to fish. The U.S. EPA reference dose is 0.01 mg/kg-day, based on blood, liver, and kidney effects in laboratory animals. Like pentachlorophenol and silvex, 2,4-D represents a challenge for CalTOX because it is an ionizable compound. This means it can exist in either if two states with very different chemical properties. At low pH values it behaves like a any of the other non-ionizable chemicals with some vapor pressure and low solubility in water. At high pHs, it is ionized and therefore, has a very low vapor pressure (unmeasurable, like metals), but is much more water soluble. We have used the chemical parameters which characterize the unionized form of 2,4-D. This was done because the objective of the TTLCs is to characterize the non-groundwater pathways and the unionized form moves more rapidly in those pathways. The SERTs are designed to address the groundwater pathways. Since 2,4-D is a herbicide, the backyard garden pathway has been eliminated as a potential route of exposure for both upper and lower TTLC calculations.

Dieldrin is a chlorinated insecticide that is no longer produced in or imported into the United States. It is easily converted from aldrin in the environment and is more resistant to biodegradation than aldrin. Dieldrin is insoluble in water, and binds strongly to soil particles, and biomagnifies through the food chain. It is acutely toxic to mammals and especially to fish. The Cal/EPA oral and inhalation cancer potency factor is 16 (mg/kg-day)-1.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Endrin is a chlorinated insecticide that is no longer produced or used in the United States because of its toxicity to birds. It persists in the environment in sediments and soil and bioaccumulates in fatty tissue of animals. It is toxic to aquatic organisms. The U.S. EPA reference dose is 0.0003 mg/kg-day, based on liver effects.

Heptachlor is a chlorinated insecticide used as a termiticide in the United States. Its use is limited because of concern over its carcinogenic potential. It is moderately persistent in soil, can bioconcentrate in and is toxic to aquatic organisms. The Cal/EPA oral and inhalation cancer potency factor is 5.7 (mg/kg-day)-1, based on liver tumors in laboratory animals.

Kepone (chlordecone) is a chlorinated insecticide, related to mirex, that has not been allowed for use in the United States since 1978 and is no longer produced in the United States. It is relatively insoluble in water, binds strongly to soil particles, and has a very high potential to bioaccumulate in fish and other aquatic organisms. Kepone is moderately acutely toxic to mammals. The Cal/EPA oral and inhalation cancer potency factor is 16 (mg/kg-day)-1.

Lead, organic: The gasoline additive, tetraethyl lead, was used as the prototype for organic lead compounds. The reference dose for tetraethyl lead is 10-7 mg/kg.

Lindane (gamma HCH) is a chlorinated insecticide which is commonly used to treat head and body lice and scabies, although it is no longer manufactured in the United States. Lindane is not persistent in soil but can remain in the air for some time. It can be absorbed through the skin, lungs, and gastrointestinal tract. In the body it can break down to pentachlorophenol. Lindane is toxic to fish and birds. The Cal/EPA considers lindane to be a carcinogen with an oral and inhalation cancer potency factor of 1.1 (mg/kg-day)-1.

Methoxychlor is a chlorinated insecticide manufactured in the United States and widely used as a replacement for DDT because of its low toxicity in animals and humans. It is somewhat persistent in the environment. The targets of its toxic effects in humans are the neurological and reproductive systems. It is toxic to fish. The U.S. EPA reference dose is 0.005 mg/kg-day, based on maternal toxicity.

Mirex is a chlorinated insecticide that is chemically related to kepone and is no longer used or made in the United States. It is practically insoluble in water, binds tightly to soil particles, and has been shown to bioaccumulate in fish, other aquatic organisms, and plants. It is moderately acutely toxic to mammals. The Cal/EPA oral and inhalation cancer potency factor is 18 (mg/kg-day)-1.

Pentachlorophenol (PCP) is a chlorinated molluscicide, fungicide, and wood preservative and is manufactured and used in the United States. Since it can exist in the environment in either the nonionized or ionized state, pentachlorophenol can exhibit a range of behavior in environmental media. However, it is not as persistent as some other chlorinated chemicals. It bioaccumulates in fish and other aquatic organisms. The proposed TTLC is based on the Cal/EPA oral and inhalation cancer potency factor of 0.018 (mg/kg-day)-1. The RCRA TC threshold is based on non-carcinogenic effects. Like 2,4-D and silvex, PCP represents a challenge for CalTOX because it is an ionizable compound. This means it can exist in either if two states with very different chemical properties. At low pH values it behaves like a any of the other non-ionizable chemicals with some vapor pressure and low solubility in water. At high pHs, it is ionized and therefore, has a very low vapor pressure (unmeasurable, like metals), but is much more water soluble. We have used the chemical parameters which characterize the unionized form of PCP. This was done because the objective of the TTLCs is to characterize the non-groundwater

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

pathways and the unionized form moves more rapidly in those pathways. The SERTs are designed to address the groundwater pathways.

PCBs (polychlorinated biphenyls) are a class of persistent chemicals formerly used as coolants, lubricants, and dielectric fluids in electrical equipment. They have not been manufactured in the United States since 1977 because of their toxicity, carcinogenicity, and environmental persistence. PCBs are highly insoluble in water, bind strongly to soil, bioaccumulate in aquatic organisms and have been shown to biomagnify up the food chain. They are carcinogenic and have reproductive and endocrine effects, and are toxic to aquatic and terrestrial organisms. PCBs are a mixture of chemical isomers with a range of physical, chemical and toxicological properties. A number of different mixtures have been identified for toxicological/regulatory purposes. The chemical and physical properties used were those of PCB-1254. The Cal/EPA oral and inhalation cancer potency factor is 7.7 (mg/kg-day)-1, but the TTLCs are determined by non-cancer liver effects, which occur at lower doses than the cancer effects. It is also important to realize that non-cancer effects are based on a maximum annual concentrations rather than a time-weighed average over the exposure duration. For chlordane and PCBs, the maximum concentration occurs via the breast milk pathway during the first year of life. PCBs are regulated by the federal government under the Toxic Substances Control Act, with a regulatory threshold of 50 ppm.

Dioxins are a class of chemicals that have never been intentionally manufactured but are generated as byproducts from combustion and chemical processes. They affect the reproductive and endocrine systems. Dioxins are insoluble in water, bind strongly to soil particles, and are highly resistant to degradation. They are accumulated by aquatic organisms, providing entry into the aquatic food chain. Dioxins in air deposit onto plants, providing entry into the terrestrial food chain. The Cal/EPA oral and inhalation cancer potency factor is 130,000 (mg/kg-day)-1. 2,3,7,8 TCDD, the most potent isomer, is regulated under Title 22.

Toxaphene is a chlorinated insecticide which is no longer used in the United States because it is toxic to humans, fish, and other animals. Toxaphene persists in soil and sediments and is resistant to breakdown in the environment. It is easily absorbed through the skin and lungs. The Cal/EPA oral and inhalation cancer potency factor is 1.2 (mg/kg-day)-1, based on liver and thyroid tumors in laboratory animals.

Trichloroethylene (TCE) is a chlorinated solvent mostly used to degrease metal parts. It can move readily through soil to groundwater and can evaporate into the air. It is minimally toxic to aquatic organisms. The Cal/EPA considers TCE a potential human carcinogen with an oral cancer potency factor of 0.015 (mg/kg-day)-1 and an inhalation cancer potency factor of 0.01 (mg/kg-day)-1.

2,4,5-trichlorophenoxy propionic acid (silvex) is an herbicide which is no longer used in the United States because of health effect concerns, particularly birth defects. This chemical does not appear to be of ecological concern. The U.S. EPA reference dose is 0.008 mg/kg-day, based on liver changes in laboratory animals.

Like pentachlorophenol and 2,4-D, silvex represents a challenge for CalTOX because it is an ionizable compound. This means it can exist in either if two states with very different chemical properties. At low pH values it behaves like a any of the other non-ionizable chemicals with some vapor pressure and low solubility in water. At high pHs, it is ionized and therefore, has a very low vapor pressure (unmeasurable, like metals), but is much more water soluble. We have used the chemical parameters which characterize the unionized form of silvex. This was done because the objective of the TTLCs is to characterize the non-groundwater pathways and the

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

unionized form moves more rapidly in those pathways. The SERTs are designed to address the groundwater pathways. Finally, silvex is a herbicide, therefore, the backyard garden pathway has been eliminated as a potential route of exposure for both upper and lower TTLC calculations.

Vinyl chloride is a volatile chlorinated chemical used to make many plastic products and is most readily released to air. It is soluble in water and thus can leach through soil to groundwater. It is considered toxic to aquatic organisms. Vinyl chloride is one of the few chemicals to have been shown to cause cancer in humans. The Cal/EPA oral and inhalation cancer potency factor is 0.27 (mg/kg-day)-1, based on a rare form of liver tumors in laboratory animals.

Inorganic Chemicals

Antimony is a metal used in alloys; the oxide is used as a fire retardant. Elevated atmospheric levels can irritate eyes, lungs, and skin. Antimony is a gastrointestinal irritant. Systematically it can cause anemia, electrocardiographic anomalies and muscle or joint pain. Antimony causes reproductive and developmental effects in non-human species. The U.S. EPA reference dose is 0.0004 mg/kg-day.

Arsenic is an element used in many industrial processes. It has acute and chronic toxic effects and is a human carcinogen. The U.S.EPA oral cancer potency factor is 1.5 (mg/kg-day)-1.

Barium is an element with various medical and industrial uses. It has low toxicity to aquatic organisms. The U.S. EPA reference dose is 0.07 mg/kg-day, based on increased blood pressure in humans.

Beryllium is a metal with a variety of uses in metallurgy and consumer and industrial products. It causes acute and chronic berylliosis when inhaled, causes cancer in laboratory animals, and is toxic to aquatic organisms. The Cal/EPA oral and inhalation cancer potency factor is 7 (mg/kg-day)-1.

Cadmium is a metal used in batteries, metal plating, pigments, photography and lithography. It is released into the environment mostly through mining and refining practices and from incineration of coal and wastes. Like most other elements, cadmium is not well absorbed through the skin. Cadmium can bioaccumulate and is toxic to aquatic and terrestrial organisms. The Cal/EPA inhalation cancer potency factor is 15 (mg/kg-day)-1, based on respiratory tumors.

Chromium is an element that is an essential nutrient for humans. It is also produced by industrial processes, particularly plating, dyes and pigments, leather tanning and wood preserving. Chromium most often enters the body through ingestion and inhalation. The U.S. EPA reference dose for trivalent chromium is 1 mg/kg-day, based on no effects seen in a rat feeding study.

Hexavalent chromium is produced by industrial processes, particularly plating, dyes and pigments, leather tanning and wood preserving. Chronic inhalation of hexavalent chromium can irritate the nasal passages and lead to sensitization or lung cancer. Ingested hexavalent chromium can irritate the gastrointestinal tract and lead to toxic manifestations in the liver and kidney. Hexavalent chromium is toxic to aquatic and terrestrial organisms. The Cal/EPA oral cancer potency factor is 0.42 (mg/kg-day)-1. The Cal/EPA inhalation cancer potency factor is 510 (mg/kg-day)-1.

Cobalt is a metal used in alloys, in porcelain and in pigments. It is an integral part of Vitamin B12, an essential nutrient. It is present in the environment as a result of natural processes and of burning fossil fuels. Inhalation of excessive amounts of cobalt can cause asthma and

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

pneumonia. Ingestion of excessive amounts of cobalt has resulted in chronic cardiomyopathy. The U.S. EPA reference dose (currently under review) is 0.06 mg/kg-day.

Copper is a soft reddish metal used for many industrial and consumer products by itself or in alloys or in the form of copper compounds. It is an essential nutrient. Long-term exposure to elevated levels of copper can irritate mucous membranes and cause headaches or dizziness. Copper's greatest threat in the environment is its toxicity to aquatic organisms. Although many copper salts are soluble, in natural systems copper is usually bound to soil or sediment. The U.S. EPA reference dose is 0.037 mg/kg-day. The U.S. EPA Ambient Water Quality Criterion is 12 ug/l.

Fluoride is a halogen whose major use is addition to drinking water at concentrations around 1 mg/l as an aid in the prevention of dental caries. Excessive dosages can cause dental and skeletal fluorosis, a mottling of teeth and bones. This does not become a significant clinical problem until the dosage reaches 20–40 mg/day. The U.S. EPA reference dose is 0.06 mg/kg-day.

Lead is a metal which has been used for numerous industrial purposes and is present in the environment mostly from the past combustion of leaded gasoline. Lead is readily absorbed across the gastrointestinal tract into the blood stream and then many tissues in the body. Chronic exposure by humans has an adverse effect on many organs, most importantly, the central nervous system, even at very low concentrations. The Center for Disease Control has stated that children's blood lead level should be below 10 ug lead/dl.

Mercury is a metal used as a fungicide, in electrical apparatus, and other industrial purposes. Unique among metals, mercury can evaporate at room temperature; in this way, mercury easily enters the atmosphere, where it can be inhaled or redeposit onto soil and surface water. Mercury is toxic to aquatic and terrestrial organisms. The U.S. EPA reference concentration is 0.0003 mg/m3, based on central nervous system effects after inhalation.

Molybdenum is a metal used in making alloys, particularly where high temperature resistance is needed. It is an essential nutrient. Excessive dosages can cause reversible anemia, diarrhea, and poor growth. Higher or prolonged exposures can lead to joint deformities and degenerative changes in the liver and kidney. Copper antagonizes the absorption of molybdenum. Molybdenum is toxic to aquatic organisms. The U.S. EPA reference dose is 0.005 mg/kg-day.

Nickel is an important industrial metal used in alloys, plating, and batteries. Nickel exposures are most common in workers in these industries. Acute exposures to nickel carbonyl result in respiratory and generalized symptoms resembling viral pneumonia. Dermal contact can lead to dermatitis and hypersensitivity. Nickel subsulfide, nickel refinery dust, and probably nickel carbonyl are carcinogenic when inhaled. Chronic exposure can lead to impaired immune function. Nickel is toxic to aquatic organisms. The U.S. EPA reference dose is 0.02 mg/kg-day. The acute toxicity endpoint was allergic dermatitis in humans, reported to occur at a LOEL of 0.01 to 0.1 mg/kg.

Selenium is an element used in electronic equipment and other industrial products. It is released to the environment via natural and manufacturing processes. Humans are mostly commonly exposed to selenium through the ingestion of selenium-containing foods. Selenium is moderately toxic to aquatic organisms and very toxic to certain birds. The U.S. EPA reference dose is 0.005 mg/kg-day, based on selenosis in humans.

Silver metal and its compounds are used in photographic materials, electrical products, alloys and jewelry. Silver does not break down in the environment and is present at low concentrations in water and soil. Most of the silver released to the environment comes from photographic materials or from mining operations. Free silver ions are very toxic to aquatic organisms, but

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

are not persistent in the environment. The U.S. EPA reference dose is 0.005 mg/kg-day, based on argyria, a discoloration of the skin in humans who have absorbed a cumulative dose of at least 1 gm silver (equivalent to at least 25 gm ingested). Daily dosages associated with toxic effects in rats are much higher.

Thallium is a metal used in the electronics industry, in switches, in specialized glass, and in some medical devices. Its use as a rat poison has been banned. It is readily taken up by plants and is relatively well absorbed from the gastrointestinal tract. Toxic effects may be found in the nervous system, and the heart, liver, and kidneys. The U.S. EPA reference dose is 0.00007 mg/kg-day.

Vanadium is a metal that is used in steel-making, plastics, ceramics, and rubber. It is released to the atmosphere when fossil fuels are burned. Principal health effects involve the respiratory system, producing such symptoms as cough, chest pain, and sore throat. Vanadium is toxic to aquatic organisms. The U.S. EPA reference dose is 0.003 mg/kg-day.

Zinc is a metal that has many industrial uses by itself or in alloys. It is released to the environment from mining and industrial operations, fossil fuel combustion, and incineration of zinc-containing wastes. It is an essential nutrient. Zinc may cause digestive upsets associated (often from overdosing with zinc supplements), or impairment of pulmonary function associated with inhalation of zinc dust or fumes. The U.S. EPA reference dose is 0.3 mg/kg-day. Zinc is toxic to fish at relatively low concentrations. Aqueous solubility depends on pH, salinity, and presence of ligands and complexing agents. The U.S. EPA Ambient Water Quality Criterion is 110 ug/l.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Appendix 2: Derivation of proposed SERTs

Lower (exit-level) SERTs

The proposed lower Soluble or Extractible Regulatory Thresholds (SERTs) are based on the lowest of:

(1)  

California Maximum Concentration Limits (MCLs), or

(2)  

U.S. EPA Ambient Water Quality Criteria for the protection of aquatic life at 100 ppm total hardness or a pH of 6.5 (as applicable), or

(3)  

human-health-based levels calculated by DTSC. These values consider only exposure to humans from drinking ground water.

To calculate health-based levels for carcinogenic constituents, cancer potency factors developed by the Office of Environmental Health Hazard Assessment within the California Environmental Protection Agency (if available, otherwise U.S. EPA cancer potency factors) were used to calculate the concentration corresponding to a risk of 10-5. This risk level was chosen because it is the no-significant-risk level under the Safe Drinking Water and Birth Defects Prevention Act. The balance of the health-based values are based on U.S. EPA reference doses or on data used to develop the U.S. EPA region 9 Preliminary Remediation Goals (PRGs) for non-carcinogenic effects. Carcinogenic effects of lead were considered but were not limiting. The general equation for the health-based levels for carcinogens can be written as:

HBL = Risk /(WI × CPF × ED/AT)

The general equation for the health-based levels for non-carcinogens can be written as:

HBL = RfD/WIc

The parameters and their distributions are as follows:

Parameter

mean

st. dev.

AT (lifespan, years)

70*

7*

ED (exposure duration, yrs)

14*

16*

WI (water ingestion, combined, 1/kg/day)

0.022*

0.004*

Wic (water ingestion, child, 1/kg/day)

0.029*

0.01*

Cancer Potency Factors (kg-day/mg)

Cal/EPA (chemical-specific)

Reference dose (mg*kg-1*day-1)

U.S. EPA RfD or region 9 PRG

* Values from CalTOX

All health-based values are 10th percentile estimates of the concentrations that would correspond to the stated level of risk or hazard. This means that for an individual picked at random from an exposed population there is theoretically a 10% chance that the true risk is higher than 10-5 for carcinogens or that the true hazard index is larger than 1 for non-carcinogens. Conversely, there is a 90% chance that the true risk is lower than 10-5 or that the

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

true hazard index is less than 1. The 10th percentile was chosen to balance protectiveness and practical considerations.

A limitation of this probabilistic approach is that it is only as accurate as the distributions that are put into the model. The quantity and quality of data from which to construct parameter distributions is highly variable. Unfortunately, there are no widely accepted distributions for the toxicity parameters, so conservative estimates are used: 1) Cancer potency slopes are statistical 95th percentile estimates of the slope of the line describing the relationship between carcinogen dose and probability of cancer in the test species; 2) the most sensitive species and sex are used (unless there are satisfactory human data); 3) humans are usually assumed to be 6 times as sensitive to carcinogens as rats and 14 times as sensitive as mice (when rodent studies are relied upon); and 5) it is assumed that at low dosages the relationship between the exposure to the carcinogen and the probability of neoplasia is linear with no threshold. For non-carcinogens, uncertainty factors are usually incorporated to compensate for possible differences between species and to protect the most sensitive individual. For these reasons, there is much less than a 10% chance that the true risk is as high as 10-5 or that the true hazard index is larger than 1, but this extra conservatism can only be considered qualitatively.

The calculated values also include the implicit assumption that the waste containing the constituent in question is undiluted in the landfill. This is a conservative assumption because, in reality, most waste would be mixed with other wastes which do not contain the constituent being evaluated (unless the waste is disposed of in a monofill, in which case the assumption that the waste is co-disposed with decomposing organic matter would not apply), and leachate which came in contact with the waste would be diluted by leachate which did not contain the constituent in question. Thus, it is assumed that the concentration of the constituent in the TCLP extract is a good representation of the concentration of the constituent in landfill leachate after mixing with leachate from the entire landfill cell.

The calculated values consider ingestion of groundwater as the only human exposure pathway. Bioaccumulation (increasing body burden over time) is taken into account because the toxicity benchmarks are usually based on studies involving lifetime exposure (and if not, uncertainty factors are incorporated to account for less-than-lifetime exposure).

To calculate the proposed SERT, the MCL, AWQC, or HBL (whichever was lowest) was multiplied by a dilution/attenuation factor of 100. (This factor is the same as that used by U.S.EPA in developing the RCRA Toxicity Characteristic regulatory limits, and is intended to account for the dilution and attenuation that occur as leachates move through the unsaturated zone and mix with ground water. U.S. EPA is in the midst of a project to develop chemical-specific dilution/attenuation factors. DTSC will track the progress of this effort, and consider adopting chemical-specific dilution/attenuation factors when these are developed.) The resulting value was compared with the estimated quantitation limit (EQL) × 2, and the higher value (rounded to one significant figure) became the proposed SERT.

SERTs for antimony, arsenic, molybdenum, selenium, and vanadium are not intended to be applied to solid wastes because the extraction test (the Toxicity Characteristic Leaching Procedure or TCLP) does not reliably predict leaching of these elements from solid wastes.

SERTs that exceed 1/20 of the corresponding TTLC are not intended to be applied to solid wastes. This is because there is a 20-fold dilution inherent in the TCLP methodology and therefore a waste could not exceed a SERT without also exceeding the TTLC unless the SERT

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

is less than 1/20 of the TTLC, even if the constituent is 100% soluble or extractable. All SERTs apply to liquid wastes unless the TTLC is lower.

The lower (exit-level) SERT for arsenic was calculated as follows: The health-based drinking water concentration limit, based on an oral carcinogenic potency of 1.5 (mg/kg/day)-1 and a risk of 10-5, was 0.007 mg/l. However, the ninetieth percentile arsenic concentration in California drinking water supplies in 1994 as measured by the Department of Health Services was 0.01 mg/l. DTSC's mandate to protect public health and the environment does not include regulation to below background concentrations, and therefore we propose to use 0.01 mg/l as the target arsenic concentration limit in ground water. With an assumed dilution/attenuation factor of 100, the limit in liquid waste would be 1 mg/l. In the following table, proposed SERTs are compared with other regulatory criteria.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Basis for Lower SERTs and comparison with current regulatory thresholds (mg/l)

 

Health-based level × 100

CA MCL × 100

AWQC × 100f

EQLh × 2

proposed lower SERT

Current STLC

RCRA RL

Aldrin

0.006a

none

0.3

0.0007

0.006

0.14

none

Chlordane

0.002a

0.01

0.0004

0.0007

0.0007

0.25

0.03

DDT & metabolites

0.7a

none

0.0001

0.0005

0.0005

0.1

none

2,4-,D

30b

7

none

0.004

7

10

10

Dieldrin

0.01a

none

0.0002

0.0009

0.00099

0.8

none

Endrin

1b

0.2

0.0002

0.0008

0.0008

0.02

0.02

Heptachlor

0.04b

0.001

0.0004

0.0008

0.0008

0.47

0.008

Kepone

0.006a

none

none

0.04

0.04

2.1

none

Lindane

0.2a

0.02

0.008

0.0005

0.008

0.4

0.4

Methoxychlor

20b

4

0.003

0.002

0.003

10

10

Mirex

0.01a

none

0.0001

0.0003

0.0003

2.1

none

Pentachlorophenol

10a

0.1

0.4

0.002

0.1

1.7

100

PCB

0.03a

0.05

0.001

0.02

nonei

5

none

2378 TCDD

2e-6a

3e-6

none

2e-9 to 2e-8

nonei

0.001

none

Toxaphene

0.2a

0.3

0.00002

0.002

0.002

0.5

0.5

TCE

20a

0.5

none

0.01

0.5

204

0.5

2,4,5-trichlorophenoxy

30b

5

none

0.002

5

1

1

Vinyl chloride

3

0.05

none

0.01

0.05

5

5

Antimony

1b

0.6

3

1

1

15

none

Arsenic

0.07a

5

20

0.2

1e

5

5

Barium

200b

100

none

4

100

100

100

Beryllium

0.02a

0.4

0.5

0.1

 

0.75

none

Cadmium

2b

0.5

0.1

0.1

0.1

1

1

Chromium+6

0.2a

none

1

0.02

0.2

5

none

Chromium, total

3000b

5

20

0.2

5

560

5

Cobalt

200c

none

none

1

200

80

none

Cooper

100b

none

1

0.5

1

25

none

Flouride

200b

none

none

1

200

80

none

Mercury

1b

0.2

0.001

0.004

0.004

0.2

0.2

Molybdenum

10b

none

none

1

10

350

none

Nickel

70b

10

20

0.8

10

20

none

Lead

20d

1.5

0.3

0.06

0.3

5

5

Selenium

20b

5

0.5

0.1

0.5

1

1

Thallium

0.2b

0.2

40

0.2

0.2

7

none

Vanadium

20b

none

none

1

20

24

none

Zinc

1000b

none

10

0.4

10

250

none

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Footnotes for preceeding and following tables

a. Based on California or U.S. EPA cancer potency factor with CalTOX exposure parameters.

b. Based on current U.S. EPA reference dose with CalTOX exposure parameters.

c. Based on U.S. EPA region 9 preliminary remediation goals

d. DTSC's lead risk assessment spreadsheet was used to determine the health-based level.

e. The proposed SERT for arsenic is based on CA background

f. Based on federal Ambient Water Quality Criteria © 100 ppm hardness or a pH of 6.5 and longest available exposure

g. Based on estimated quantitation limit

h. No lower SERT proposed (see text)

Upper SERTs

The proposed upper SERTs were calculated by multiplying the lowest of the HBL, the MCL, or the AWQC by the DAF of 100 and by a liner protection factor (LPF). The liner protection factor reflects the assumption that wastes which are not classified as hazardous will require disposal in at least a single composite-lined landfill if they are land-disposed. The possible values of LPF (Tab 13) were entered as a custom distribution into the spreadsheet used to calculate SERTS. This distribution, along with the distributions for other variable parameters used in the SERT calculations, were propogated through the model to yield a distribution of possible values for each upper SERT. The resulting value is compared to the upper EQL x 2 and the higher value is the proposed upper SERT. As discussed earlier, the tenth percentile of this distribution is the proposed upper SERT.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Basis for Upper SERTs and Comparison with Current Regulatory Thresholds (mg/l)

 

HBL × 100

MCL × 100

AWQC × 100f

EQLh × 2

LPF

upper SERT

Current STLC

RCRA RL

Aldrin

0.006a

none

0.3

0.007

63

0.4

0.14

none

Chlordane

0.002a

0.01

0.0004

0.007

18

0.008

0.25

0.03

DDT & metabolites

0.7ò

none

0.0001

0.005

18

0.005

0.1

none

2,4-,D

30b

7

none

0.04

18

100

10

10

Dieldrin

0.01a

none

0.0002

0.009

18

0.009

0.8

none

Endrin

1b

0.2

0.0002

0.008

18

0.008

0.02

0.02

Heptachlor

0.04b

0.001

0.0004

0.008

18

0.008

0.47

0.008

Kepone

0.006a

none

none

0.4

63

0.4

2.1

none

Lindane

0.2a

0.02

0.008

0.005

18

0.1

0.4

0.4

Methoxychlor

20b

4

0.003

0.02

18

0.05

10

10

Mirex

0.01a

none

0.0001

0.003

18

0.003

2.1

none

Pentachlorophenol

10a

0.1

0.4

0.02

18

2

1.7

100

PCB

0.03a

0.05

0.001

0.2

18

5e

5

none

2378 TCDD

2e-6a

3e-6

none

2e-8 to 2e-7

63

?

0.001

none

Toxaphene

0.2a

0.3

0.00002

0.02

18

0.02

0.5

0.5

TCE

20a

0.5

none

0.1

18

9

204

0.5

2,4,5-trichlorophenoxy

30b

5

none

0.02

18

90

1

1

Vinyl chloride

3

0.05

none

0.1

18

0.9

5

5

Antimony

1b

0.6

3

10

18

10

15

none

Arsenic

0.07a

5

20

2

63

5

5

5

Barium

200b

100

none

40

18

2000

100

100

Beryllium

0.02a

0.4

0.5

1

63

1

0.75

none

Cadmium

2b

0.5

0.1

1

18

2

1

1

Chromium+6

0.2a

none

1

0.2

63

20

5

none

Chromium, total

3000b

5

20

2

18

90

560

5

Cobalt

200c

none

none

10

24

4000

80

none

Cooper

100b

none

1

5

18

20

25

none

Flouride

200b

none

none

10

24

4000

80

none

Mercury

1b

0.2

0.001

0.04

18

0.04

0.2

0.2

Molybdenum

10b

none

none

10

24

300

350

none

Nickel

70b

10

20

8

18

200

20

none

Lead

20d

1.5

0.3

0.6

18

5

5

5

Selenium

20b

5

0.5

1

18

9

1

1

Thallium

0.2b

0.2

40

2

19

4

7

none

Vanadium

20b

none

none

10

24

500

24

none

Zinc

1000b

none

10

4

18

200

250

none

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Solubility, STLCs, and TTLCs

At present, there is no established laboratory procedure that satisfactorily estimates the leachability of antimony, arsenic, molybdenum, selenium, and vanadium from a variety of wastes. For these elements, DTSC evaluated the protectiveness of the TTLCs with respect to groundwater protection using the following approach: First, the fraction of the measured total concentration that is available for leaching was determined as follows. In a study conducted by DTSC, five composite wastes were analyzed for total concentration of the five elements and also reacted with leachates from seven landfills representing the spectrum of landfills in California. The extracted element concentration in those leachates were measured. For each leachate-waste combination a leachate-extractable concentration/total concentration ratio was computed. The highest ratio among all of the leachate-waste combinations (shown in the last column of the table below) represents the greatest extraction of the element by landfill leachate. Second, the maximum dissolved: total concentration ratio in the last column was multiplied by the proposed upper or entry TTLC. This computed maximum concentration in the leachate represents the leachate concentration that would result from the dissolution of the element present in the waste at the TTLC concentration with the most aggressive landfill leachate. The following table shows the proposed upper and lower TTLCs, the STLCs and computed maximum concentrations (in mg/l) in the leachates.

element

proposed upper TTLC (mg/kg)

STLC (mg/l)

computed maximum leachate conc.1

propose d lower TTLC (mg/kg)

STLC (mg/l)

computed maximum leachate conc.1

maximum dissolved: total ratio (mg/l÷mg/kg)

antimony

700

15

0.21

700

15

0.21

0.0003

arsenic

50

5

0.65

50

5

0.65

0.013

molybdenum

9,000

350

342

9,000

350

342

0.038

selenium

9,000

1

369

50

1

1.6

0.041

vanadium

10,000

24

180

2,000

24

36

0.018

1. The product of the TTLC and maximum dissolved:total ratio

Comparison of the adjacent shaded columns shows whether the predicted maximum extractable concentration exceeds the STLC. If it does, as in the case of the bolded values for selenium and vanadium, the TTLC would not be protective. In all other cases the computed maximum leachate concentration is less than the STLC. For selenium and vanadium, DTSC proposes to reduce the TTLCs to compensate for the inability of the TCLP to reliably predict the extraction of these elements from wastes. As shown below, TTLCs of 1000 for vanadium and 30 for selenium would result in maximum expected leachate concentrations which are less than STLCs.

element

proposed upper TTLC (mg/kg)

STLC (mg/l)

computed maximum leachate conc.

propose d lower TTLC (mg/kg)

STLC (mg/l)

computed maximum leachate conc.

maximum dissolved: total ratio (mg/l÷mg/kg)

selenium

30

1

1.2

30

1

1.2

0.041

vanadium

1000

24

18

1000

24

18

0.018

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Appendix 3: TTLCs

Introduction

What is the purpose of this appendix?

The concept paper includes a table of upper and lower Total Threshold Limit Concentration (TTLC) values for 38 chemicals. The concept paper describes how the upper and lower TTLC values are to be used in classifying a waste. This appendix describes the rationale for determining the values in the table.

What is the relationship between ground water and TTLCs?

The soluble or extractable fraction of the waste is that portion which may reach ground water. The TTLC tables and this appendix do not address the issues associated with the soluble fraction of waste (except in the case of chemicals for which the extraction test is found not to predict the leachable fraction). These are addressed by Soluble or Extractable Regulatory Thresholds (SERTs), described in Appendix 2.

Why are TTLCs developed for individual chemicals instead of waste streams?

The likelihood of adverse effects on health is proportional to the amount of a specific chemical people take into their bodies. Information is available in the scientific literature relating toxic effects in humans and animals to amounts of individual chemicals. The concentration in the waste of a specific chemical and published information about its toxicity are used to determine if a waste is hazardous. However, there is little scientific information on the toxicity of waste streams and additive or synergistic effects among individual chemicals. Testing of all California waste streams for toxic effects in laboratory animals would be neither cost-effective nor humane. Therefore, for purposes of comparison with TTLCs, wastes are analyzed for known toxic chemicals. The fish bioassay measures additive and/or synergistic effects.

Why were these 38 chemicals selected?

The objective of the Regulatory Structure Update project is to perform a critical review of current California hazardous waste regulations. Total Threshold Limit Concentrations (TTLCs) were determined to be important to retain because they have no counterpart in federal law. The Department believes that a multimedia approach to protection of public health and the environment is necessary. This effort is intended to improve the scientific basis of the TTLCs for the 38 chemicals which currently have TTLCs. Vinyl chloride has been added to the list because it is a chemical of commercial relevance which appears on the list of carcinogens in the current regulations.

What is the purpose of two tiers of TTLCs?

TTLCs (along with the other criteria) are intended to facilitate classification of wastes according to the hazard they pose. Such classification will allow us to determine which wastes should be regulated in order to protect people and ecosystems from exposures to toxic chemicals during the handling and disposal of wastes. TTLCs should protect workers and residents from chronic health effects (effects over long periods of time)- The two-tier TTLCs would be used to classify wastes into three groups: 1) fully regulated hazardous wastes, 2) special wastes, with reduced regulatory or 3) no regulatory requirements imposed by DTSC. Wastes with concentrations above the upper TTLC value would be in group 1, wastes with concentrations lower than the lower TTLC would be in group 3 and wastes with any constituent concentration levels between the upper and lower TTLCs would be in group 2, provided that they were not classified in group 1 by any other characteristic.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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How are the upper and lower (exit-level) TTLCs selected?

The proposed TTLC concentration for each chemical was selected from among several different concentrations in a two-step process that was nearly identical for both upper and lower TTLCs. First, the lower of two risk-based concentrations intended to protect human health and/or the environment was selected for each chemical. Second, the risk-based concentration was compared with two practical limitations: the limit of quantitation and the ambient concentration in the environment. The highest of the risk-based, ambient or quantitation limit concentration was selected for each chemical. The following diagram shows the decision process for selection of the TTLCs.

Figure 1: Decision Tree for Determining Exit TTLCs for Each Chemical

Figure 1 shows that for each chemical a decision was made to select a concentration that would protect both residents and non-human species living on or near land to which waste containing the TTLC chemical had been added. The scenario for residents is called the Land Conversion Scenario because the land is converted from uninhabited land to inhabited residential lots after waste ceases to be plowed into the soil. Once the lower of the two risk-based values was selected, this value was compared to both an estimated quantitation limit and, if available, an ambient concentration in soil. A policy decision was made to use the highest of these three concentrations. Thus, regulatory thresholds which are limited by quantitation limits or ambient concentrations could pose a theoretical risk exceeding the target risk to human health or the environment. The reasons for these decisions are as follows:

  • Twice the Estimated Quantitation Limit was selected if it exceeded the risk-based value because regulated industries must be able to measure the TTLC concentration in order to determine if one is complying with the law.
  • It is not reasonable or practical to define large amounts of native California soil as hazardous. Thus, if the risk-based concentration of any element was less than the maximum concentration measured in 50 samples of native California soils, a value based on the native soil ambient concentration was selected.

More detailed descriptions of the detection limit and ambient soil concentrations can be found under the

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Figure 2: Decision Tree for Determining Upper TTLCs for Each Chemical

Figure 2 shows that for each chemical a decision was made to select a concentration that would protect both residents living near a facility in which waste containing the chemical is handled, and workers handling that waste. The computation of the concentrations based on the residential Landfill Scenario and the Waste Worker are described below under subheadings with those titles. Once the lower of the two risk-based values was selected, this value was compared to both an estimated quantitation limit and, if available, an ambient concentration in soil.. A policy decision was made to use the highest of these three concentrations. Thus, regulatory thresholds which are limited by quantitation limits or ambient concentrations could pose a theoretical risk exceeding the target risk to human health or the environment. The reasons for these decisions are as follows:

  • Twice the Estimated Quantitation Limit was selected over a risk-based value because regulated industries must be able to measure the TTLC concentration, otherwise, it is not possible to determine if one is complying with the law.
  • Worldwide ambient concentrations of dioxins and dibenzofurans exceed calculated health-based concentrations. Therefore, a value based on U.S. and U.K. ambient concentrations was selected as the basis for the proposed TTLC.

More detailed descriptions of the detection limit and ambient soil concentrations can be found under the appropriate subheadings below, and under tabs 5a and 5b.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

First Stage: Computation of Risk-Based TTLCs

How is quantitative risk assessment used to assess effects on human health and the environment?

Risk assessment is the process of establishing a relationship between a chemical source (such as waste in a municipal landfill) and an adverse effect (such as risk of human cancer). A quantitative risk assessment establishes a mathematical relationship between a concentration of a chemical at a source, such as the soil in a residential lot or waste in a landfill, and the risk of an adverse health effect in people living on or near the source. Risk assessment comprises two parts:

1) Toxicity Assessment

Toxicity assessment pertains to the relationship between the risk of an adverse health effect and the dose or amount of chemical taken into the body. Knowledge about this relationship comes from toxicological studies (laboratory experiments with animals) and epidemiological studies (surveys of the health condition of humans). Different chemicals may induce different adverse health effects, but there is a relationship between the dose of the chemical and the likelihood or risk of the undesired effect. Toxicity assessment is chemical-dependent and independent of the exposure scenario.

Toxicity assessment is performed by the California Office of Environmental Health Hazard Assessment (OEHHA) and the U.S. EPA Office of Research and Development (USEPA-ORD). OEHHA and the USEPA have established a mathematical relationship between dose and the likelihood of getting cancer. Such a relationship between dose and risk of cancer is called a cancer potency factor. If an OEHHA potency factor exists for a specific chemical, this value is used in relating risk to dose. If no OEHHA potency factor exists, the USEPA potency factor is used. The USEPA has established reference doses (RfDs) that relate risk of non-cancer effects to a given dose. DTSC uses USEPA RfDs to establish maximum allowable daily doses for chemicals that cause non-cancer effects.

2) Exposure Assessment

Quantitative exposure assessment is the relationship between the source (such as a chemical concentration in a municipal landfill) and the dose a person may receive. Exposure assessment is based on an exposure scenario, such as a resident living near a municipal landfill. Sometimes these relationships are described by simple algebraic equations. Maximum contaminant levels (MCLs) used to regulate drinking water supplies are based on such a mathematical relationship. Other times the relationships are more complex and require complex equations, such as the description of the movement of a chemical from soil into groundwater below the site and transport of that ground water off-site to some location where it is used as drinking water. Therefore, attributes of the chemical, the landscape, and the people living in the area are all important to understand the dose the people may receive for a given concentration in the soil or landfill.

What is multimedia exposure assessment?

A multimedia, multiple pathway exposure assessment is a mathematical or quantitative relationship between the concentration of a chemical in a waste in a specific location and the daily dose received by people or non-human species. The exposure assessment has three steps.

The first step is to characterize the uptake of a chemical from the environment into the body. Chemical vapors and contaminated dust in air may be inhaled. Contaminated water, soil and food may be eaten and contribute to the total daily dose. Chemicals may be absorbed through the skin from contaminated soil and water in contact with the skin. The exposure media are air, water, soil and food which are inhaled, ingested, or comes into contact with the skin. Mathematical equations relate the concentration in the exposure media to the total daily dose.

Second, mathematical relationships must be established between the concentration of chemical in the exposure media (inhaled air, ingested water, soil that contacts skin, etc.) and the environmental media at

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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the landfill. Note that exposure media are distinct from environmental media. Environmental media are the air, ground water, surface water and soil which are located above, below or adjacent to the waste. Nearby residents do not breath air which is directly above the landfill or have direct contact with landfill constituents. Therefore, it is important to establish mathematical relationships between the environmental and exposure concentrations for all relevant media by using a multimedia exposure assessment model.

Third, chemicals in the waste may move upward into the air, downward into the groundwater, partition into plants growing near the waste or migrate into nearby surface water. Therefore, equations are needed that are consistent with known scientific principles to establish a relationship between the chemical in the landfill waste and several of the environmental media in the vicinity of the landfill.

Mathematical Models and Regulatory Decisions

The uncertainties associated with risk assessment are enormous. Some people are uncomfortable with quantitative risk assessment because of this uncertainty and they feel that mathematical models suggest a degree of precision that does not exist. We believe that mathematical models can deal with uncertainty quantitatively and, therefore, their use need not imply an absence of uncertainty. Furthermore, we believe that models are essential for rational decision-making for environmental regulatory agencies. CalTOX and the PEA spreadsheets are quantitative statements about the Department's understanding in how chemicals move in the environment and cause harm to human beings. The equations in those spreadsheets are not proven facts. They must be viewed as hypotheses to update and correct as new information becomes available. The scientific process will inevitably add to our understanding of these processes, but the regulatory agencies must make decisions today. Regulatory agencies must unambiguously lay out the basis for classifying wastes. Equations like those in CalTOX and the PEA provide such an unambiguous method. It is vital that such models be viewed as tools in need of constant maintenance, because the scientific information available to decision-makers in the future will be different than it is today.

How is uncertainty treated in developing TTLCs?

Quantitative risk assessment is based on mathematical equations which relate source concentration to risk. These equations have many variables related to chemical properties, landscape attributes and human exposure parameters. Usually, the values for these variables are not known precisely. These TTLCs are going to be used throughout California. A single value for rainfall or wind speed cannot represent the wide range of rainfalls and wind speeds for all of California. Not all people will live in a house located near a landfill throughout their lives. Some people move frequently, other people stay in a single house for a long time. Since the TTLC is calculated from all these variables, a range of TTLC values is more appropriate than a single arbitrarily chosen value. Therefore, a distribution or range of values was selected for each input parameter. This distribution reflects the diversity of values for landfills found throughout California. The uncertainty and variability reflected by these distributions is propagated through the mathematical equations using a computer-based method called Monte Carlo simulation.

The result of these computer simulations is a distribution of TTLC values which reflects the uncertainty and variability in the underlying input parameters. The TTLCs in all tables are the tenth percentile of those distributions. This indicates that theoretically there is a ten percent chance that an individual living on or near the waste would have exposures exceeding the 'acceptable' dose. This does not mean that ten percent of these people are at risk of dying of cancer or some other disease. The toxicity criteria used to establish the maximum daily dose do not treat uncertainty with distributions. They are selected to protect everyone given enormous uncertainties and are highly likely to be large over-estimates the true risk. In some cases, the true risk at doses of regulatory interest may be zero. Therefore, the probability of an individual experiencing a health effect from the chemical exposure is actually very much less.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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Description of the Exposure Scenarios

In risk assessment, the combination of a source of chemical and population potentially exposed to that chemical are called an exposure scenario. Exposure scenarios must be identified to compute a risk-based TTLCs. For waste classification, the source of the chemical is determined by the disposal of the waste containing that chemical. The potentially exposed populations are the people or non-human species that may be exposed to chemicals in the waste so disposed. The assumed disposal of wastes and potentially exposed-populations are described below.

Disposal Practices

Two distinct disposal practices are assumed for the two levels of TTLCs: disposal in a solid waste landfill and land application. The upper TTLC is used to distinguish waste that can be disposed in a solid waste landfill vs. waste that must be disposed of in a hazardous waste landfill. Therefore, risks associated with solid waste landfill disposal are an appropriate basis for establishing risk-based upper TTLC levels.

The lower TTLC is used to distinguish waste that need not be regulated by DTSC from waste regulated by DTSC. The actual disposition of wastes in California is varied. Significant efforts are underway to divert wastes from landfill to recycling and alternative beneficial uses. Sewage sludge and ashes containing trace elements can be valuable soil amendments. Soil amendments are applied and tilled into land periodically. Therefore, risk associated with land application of waste was selected as the basis for establishing risk-based exit TTLC levels.

Potentially Exposed Populations

Once waste is disposed of in a landfill or applied to land, many different populations of people may be exposed to chemicals in the waste. Populations may be residents, industrial workers, commercial workers, people engaged in recreation, school children, etc. These populations are defined because their location may lead to exposure to chemicals in the disposed waste. The assessed risks are related to the total dose of chemical resulting from chronic or long-term exposures. Risk is often assessed only for the most exposed population because other people would be at less risk than the most exposed group. In general, residents living on or near sources of chemicals experience the highest chronic exposures. Therefore, a residential population was assumed for both the upper and lower TTLC disposal practices.

A number of different factors contribute to greater chronic exposure often experienced by residents as compared with other populations. Residents spend more time at their homes then other groups spend in a single location. This includes more hours each day, more days per year and more years total. Therefore, residents breath more potentially contaminated air than do other populations. In addition, residents engage in activities other populations do not which increase the number of pathways by which the chemical can theoretically travel from the disposed waste to the person. Residents can have gardens with contaminated soil in which food is grown. Gardening and yard work can lead to potentially contaminated soil in contact with the skin. Children inadvertently or deliberately ingesting soil are most likely to do so at home. The majority of tap water is likely to be consumed at home. Residents contact four different exposure media (air, water, food and soil) to a greater degree than any other group. Generally, if residents are protected and the concentrations in these media are the same for all exposed populations, all people are protected.

The media concentrations are not the same for all populations; often concentrations in workplace air and soil are much higher concentrations than at residents. Workers directly in the vicinity of the waste are likely to experience much higher air and skin contact concentration than residents living near a landfill. The workers have fewer pathways and less time of exposure, but higher concentrations. Without conducting a quantitative analysis, it is not possible to know if a worker is

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

more or less exposed than a nearby resident.

Finally, non-human species may experience the highest risk if they are particularly sensitive to the effects of the contaminant or if due to their natural history, they are more highly exposed. Therefore, if exposure can occur ecosystem effects must be examined.

The following table shows the four exposure scenarios.

Disposal Practice

Residential Population

Non-Residential Population

Solid Waste Landfill (upper TTLC)

Houses near a landfill

Workers handling waste

Land Application (exit TTLC)

Houses built on land to which waste had been applied

Ecological effects

The non-resident exposure scenarios differ between both disposal practices. Ecological effects were not evaluated for landfill disposal because those effects are not considered to be significantly different than those at hazardous waste landfill. Therefore, it is not rational to require waste to go to a hazardous waste landfill based on ecological effects, so upper TTLCs should not be based on ecological effects. A worker scenario was not explicitly evaluated for the land application disposal practice, because these workers would be less frequently exposed than would the waste worker in the landfill disposal scenario. All people are protected at least to the level of waste workers because. of a policy decision resulting from the comparison of proposed exit and upper TTLCs. If the proposed exit TTLC exceeds the proposed upper TTLC, than no exit TTLCs is proposed and no special waste category can be established for a given chemical.

Exposure Scenarios

Each of the four exposure scenarios has specific features. These features include the pathways by which a chemical moves from the disposed waste to the potentially exposed population and attributes of the exposed population.

1. Residents Near a Landfill

The upper TTLC residential scenario is people living 100 meters from a landfill accepting wastes containing the TTLC chemicals. Up to 100% of the refuse in the landfill is assumed to contain the TTLC chemical. Landfill area and depth are based on a distribution of these values taken from the Waste Management Unit Database System maintained by the State Water Resources Control Board. Four properties are needed define landfill refuse: fraction of organic carbon, water content, porosity and density. Distributions of values for these properties were taken from the literature. These values may be changed for a specific landfill with verifiable information for the purpose of a variance, but these policy and literature values will be used to compute statewide levels.

Chemicals in waste are transported from the landfill to the residents in the air either as a vapor or adhering to dust particles. The residents may inhale the chemical or it may be deposited onto the soil in the yard. People may come into contact with the contaminated soil. Depending on the chemical, it may be taken up into various foods (including meat, milk, eggs and vegetables) that are consumed by the residents. For some organic chemicals, significant amounts of the chemical can be transferred from a mother's blood into her milk end this leads to high doses to breast-feeding infants.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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2. Waste Workers

The other upper TTLC exposure scenario is designed to assess the risk of workers handling the waste. These workers are assumed to handle undiluted waste either before arrival at the landfill or at the landfill. The pathways include inhalation of dusts and/or vapors, inadvertent ingestion of small amounts of waste and uptake of the waste through skin.

3. Resident on Converted Land

A policy decision was made to replicate the assumptions of land application used by U.S. EPA in deriving the maximum concentrations allowed in biosolids (CFR Part 503). These assumptions include an estimate of 0.7 kg waste per m2 of land for 20 years. After the last application, residential homes are built on the land. The residents have attributes identical to those described above (resident near the landfill) except that they also eat fish from a surface water body adjacent to the land onto which the chemical was applied.

4. Ecosystem Effects

Protection of ecosystems was accomplished through a tiered method. The first tier relied on the risk assessments conducted by the U.S. EPA in support of the Hazardous Waste Identification Rule (HWIR). HWIR is an effort similar to the setting of TTLCs. The objective is to define a concentration in waste that could be used to determine a regulated waste from an unregulated waste. HWIR has computed concentrations for most of the TTLC chemicals based on residential exposure and a variety of ecological effects. Most of the residential based levels are protective of ecological effects, therefore, no further work was done on those chemicals. Ecologically based TTLCs were derived for those chemicals that were driven by ecological concerns in the HWIR studies.

Models used for determining risk-based criteria for the scenarios

Four basic models or approaches were used in determining the concentrations for the four different scenarios shown in Figures 1 and 2. Different models were used for organic chemicals, inorganic lead and all other inorganic chemicals. Table 1 shows the the method name for each chemical-scenario combination.

Table 1: Computational Models Used for the Twelve Scenario-Chemical Combinations

Criteria

Upper TTLC Calculations

Lower TTLC Calculations

Scenario Modeled

Residents near landfill

Waste workers

Residents on converted land

Ecological concerns

Organic Chemicals

CalTOX landfill

PEA Worker Organic

CalTOX Land Conversion

Multi-tiered Process

Inorganic Lead

LeadSpread Off-site

LeadSpread Worker

LeadSpread Land Conversion

Multi-tiered Process

Inorganic Chemicals

PEA Off-site

PEA Worker Inorganic

PEA Land Conversion

Multi-tiered Process

Modified versions of the CalTOX model were used for the residential scenarios for organic chemicals for both the upper and lower TTLC. Modified versions of the LeadSpread model were used for all human

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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exposure scenarios to inorganic lead. Modified versions of the Preliminary Endangerment Assessment (PEA) model were used for all human exposures to inorganic chemicals other than lead and waste worker exposure to organic chemicals. The ecological effects for all chemicals were evaluated by using a screening process to identify chemicals for which ecological effects occurred at lower doses than for human health effects.

What is CalTOX and why was it chosen?

The CalTOX risk assessment framework is a comprehensive multiple pathway, multimedia approach to relating risk and concentration of chemical in soil. This model is an extension of the current US EPA risk assessment policy defined in the Risk Assessment Guidance for Superfund (RAGS) series. The model represents the state of the art in modeling multimedia distribution of environmental contaminants and multipathway exposures of human populations. Among the distinguishing features of CalTOX acknowledged by its reviewers are explicit treatment of mass conservation and chemical equilibrium, calculation of gains and losses in multiple environmental media compartments (air, soil, groundwater, etc.) over time by accounting for both transport among the compartments and transformation within compartments, and the quantitative and comprehensive treatment of uncertainty and variability. The model for on-site exposure (when the people live on contaminated soil) has been extensively peer-reviewed and received numerous commendations. US EPA's scientific advisory panel referred to it as ''. . . potentially the most advanced of all of the models reviewed with respect to exposure...'' in a report on Human Exposure Assessment. The Cal/EPA Risk Assessment Advisory Committee describes the model favorably. During its development, comments were solicited from internationally known scientists and are summarized in Part IV of the technical document describing the model. CalTOX is recognized as a leading model for the kind of approach it implements in multimedia risk assessment.

This model is shown in schematic form in Figure 1. An initial chemical concentration is specified for either the root zone soil or the vadose zone soil. Over time the chemical flows in the direction of the arrows, the rate at which it flows for any given arrow is dependent on the properties of the chemical and the environment. The model is divided into three groups of equations: exposure assessment based on RAGS, multimedia transport and intermedia transfer. The RAGS exposure equations represented on right of the diagram defines how much chemical people take into their body from four contaminated exposure media: food, air, water and soil. The multimedia transport equations represented on the left predicts the concentration in seven environmental compartments at various points in time. The intermedia transfer represented in between relate the concentration in exposure media to concentrations in the environmental compartments.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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Figure 1: Diagram of the CalTOX model

What modifications have been made to CalTOX and why?

The current version of CalTOX, CalTOX 2.3, is designed to assess risk to people living on or nearby soil containing a fixed concentration of chemical. CalTOX 2.3 is not designed to model risks to people living near a landfill or continuous addition to soil followed by occupation by residents. Therefore, two modified versions of CalTOX 2.3 were created to model the landfill and converted land scenarios. Both modifications required changes to the equations in the model as well as changes in the default input parameters.

CalTOX Landfill was created by transforming the root zone compartment of CalTOX 2.3 into a landfill compartment. This involved two changes to the model structure and several different input variable values. The first change in the model was to relate the landfill compartment concentration to the waste concentration by allowing the use of a waste dilution factor. The second change was to add an estimate of transport of chemical in gases produced in the landfill (carbon dioxide and methane) from the landfill compartment to the air. Landfills have different areas and depths than residential yards. Landfill contents have different properties than soil. Therefore, mean estimates of those parameters were selected based on literature values. Neither the waste dilution factor nor the distance off-site were treated stochastically. These were viewed as policy decisions. The waste dilution factor chosen was one, and residents were located 100 meters off-site.

CalTOX Land Conversion was created by computing the root soil concentration from an application rate, mixing depth, application duration and waste concentration rather than specifying an initial root soil concentration. The values for these new parameters were the point estimates cited in the US EPA technical background document used in promulgating the regulations for biosolid application to land

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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(40CFR Part 503.13). Therefore, like CalTOX Landfill, a relationship is established between health risk and waste concentration rather than root soil concentration.

Detailed descriptions of the exact changes to CalTOX 2.3 are described in the report CalTOX Adaptations for Derivation of Exit and Upper TTLC Criteria located in Tab 4a of the NAS notebook. The two modified spreadsheets were used to compute distributions of waste concentrations for each of the organic chemicals. The 10th percentile of each of these distributions was identified and presented in Table 3 shown below.

CalTOX was not used to model inorganic chemicals, including lead, because estimates of the soil- water partition coefficient (Kd) is required for each chemical. For organic chemicals, the Kd can be estimated from chemical properties and the properties of the soil. Such estimates are not possible with inorganic chemicals because their interaction with soil is more complicated. Therefore, models other than CalTOX were required for inorganic chemicals.

What is the Lead spreadsheet model and why was it chosen?

More data are available on source concentrations, like soil, and human blood lead concentrations of lead than any other chemical. These data have been used to develop a model for predicting a relationship of the soil concentration of lead and potential health effects. This model is implemented as a Department of Toxic Substances Control Lead Risk Assessment Spreadsheet (LeadSpread). Like CalTOX, LeadSpread was designed for hazardous waste sites, and it has been used by the Department for evaluating the risk associated with contaminated soil for approximately six years. Slight modifications were needed to adapt the model for use in establishing human-health-based candidate TTLCs for lead. The model and its modifications for this application are described in more detail, and example spreadsheets can be found under Tab 4b.

What modifications have been made to the Lead spreadsheet model and why?
  • LeadSpread Off-site was used to compute the risk to residents living 100 meters from a landfill containing lead wastes. For the offsite version used in the calculation of upper TTLCs for nearby residents, a soil dilution factor of 0.00098 is incorporated to estimate the concentration in off-site soil from the concentration in the waste. This value was derived from calculations for other inorganics using the PEA model (tab 4c), and affects the soil ingestion, plant ingestion, and dermal exposure pathways.
  • LeadSpread Land Conversion was used to compute the risk to residents moving into homes built on soil into which waste had been mixed.
  • LeadSpread Worker was used to to compute the risk to workers handling the waste.
What is the Preliminary Endangerment Assessment model and why was it chosen?

CalTOX was not appropriate to use for estimating risks and hazards for the worker scenario on-site for organic chemicals, because the fate and transport capability of CalTOX was not needed, and because worker exposure does not include the indirect pathways of consumption of meat, milk, eggs, and homegrown produce. CalTOX also lacks input distributions for important fate and transport parameters for inorganics. DTSC (1994) published a model useful for these scenarios in its "Preliminary Endangerment Assessment Guidance Manual" (PEA). The PEA model was successfully adapted to estimate TTLCs for inorganic constituents in wastes and for worker-based TTLCs for organics.

The PEA is an adaptation of the methods recommended by USEPA (1989) in "Risk Assessment for Superfund" (RAGS). The PEA method has been in use in DTSC's Site Mitigation Program for several years. Since both CalTOX and the PEA model are based on RAGS, the intake equations for

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
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exposure and the toxicity criteria are identical in the PEA and CalTOX. However, CalTOX considers additional pathways not considered in the PEA equations.

Figure 2. Preliminary Endangerment Assessment Model

What modifications have been made to the PEA and why?

Like CalTOX and Leadspread, the PEA was designed for hazardous waste sites. Since none of the applications of PEA in calculating TTLCs is identical to a hazardous waste site, some modifications had to be made. The PEA method was translated into spreadsheet form to estimate TTLCs for three scenarios: exposures to organic and inorganic chemicals for on-site hazardous waste workers, exposure to inorganic chemicals for a resident near a landfill, and exposure to inorganic chemicals for a resident on converted land (Table 1).

1. On-Site Hazardous Waste Worker

This differed from the original PEA model in two ways. First, the receptor is a worker, whereas the original PEA used a residential setting. Second, the landscape is a landfill or waste handling facility, whereas the original PEA used a residential landscape. Two spreadsheets were constructed, entitled "PEA Worker Organic" and PEA Worker Inorganic". Because of the necessity to model vapor emissions for organic chemicals, the spreadsheet model for organics is considerably more complex than the one for inorganic constituents. The PEA on-site worker version models only inhalation of vapors and dust, dermal contact with soil, and ingestion of soil.

2. Resident Near a Landfill

This exposure setting was similar to the original PEA in that it is residential, but it differs in that the source of toxicants is dust blowing from the landfill or other waste facility to settle on residential soil. The off-site resident was exposed directly to inhaled dust from the facility, but exposures from soil ingestion, and dermal contact with soil included assumptions about dilution of windblown dust into residential soil over a period of years. For convenience, the model was divided into two spreadsheets, "PEA Offsite Hazard", and "PEA Offsite Risk".

3. Resident on Converted Land

This exposure setting is residential, as for the original PEA, but for this scenario, a dilution factor is applied to all four exposure pathways: ingestion of soil, dermal contact with soil, ingestion of homegrown produce, and inhalation of dust. The dilution arises as waste is applied to and mixed

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

with soil over a period of years. Thus, the target concentration in the waste is higher than the concentrations to which the resident will eventually be exposed. It was assumed that this activity will resemble application of sewage sludge to agricultural land, followed by conversion of the land to residential use. For convenience, the model was divided into two spreadsheets, "PEA Land Conversion Hazard", and "PEA Land Conversion Risk".

How were effects on non-human species evaluated?

The candidate lower (exit-level) TTLCs based on human health were reviewed to determine whether or not they would protect non-human species (see Tab 4d for details). Upper TTLCs were not similarly reviewed because protection of ecological resources is thought to be similar in Class 1 versus Class 2 or 3 landfills. A tiered screening approach was adopted due to the lack of an accepted risk assessment method for ecological toxicity. The first screen consisted of a comparison of the human toxicity exit concentration to the ecological toxicity exit for each chemical in the review drafts of the USEPA Hazardous Waste Identification Rule (HWIR, 1). For 29 of the 37 chemicals being analyzed, there were HWIR exit concentrations for both humans and ecosystems. The other eight were considered low priority in the HWIR analysis and therefore are not likely to present significant threats to ecosystems at concentrations below those that would be of concern for human health.

For 18 of the 29 chemicals the human toxicity exit concentration was lower than the ecological toxicity exit concentration, indicating that for those 18 chemicals, human-health-based lower TTLCs would be likely to also protect other species. For hexavalent chromium, the human-health based TTLC is the same as the HWIR ecological exit concentration. The remaining ten chemicals - endrin, methoxychlor, lead, mercury, selenium, nickel, vanadium, cadmium, zinc, and copper - moved to the second screen.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Table 2: HWIR Human-Ecological Risk Comparison

Chemical

HWIR human exit level*

HWIR ecological exit level*

Aldrin

0.00009

0.008

Chlordane

0.002

4

DDT & congeners

0.0002

0.004

2,4 D

600

none

Dieldrin

0.0003

0.05

Dioxin

5e-7

1e-6

Endrin

0.6

0.1

Heptachlor

0.8

20

Kepone

0.0003

3

Lead (organic)

none

none

Lindane

0.009

0.2

Methoxychlor

300

3

Mirex

none

none

Pentachlorophenol

0.5

50

Polychlorinated biphenyls

0.0007

0.05

Tricholoethylene (TCE)

10

none

Toxaphene

0.00003

0.001

Silvex

100

400

Vinyl chloride

0.06

none

Antimony

2

4

Arsenic

0.08

10

Barium

2000

4000

Beryllium

0.01

20

Cadmium

10

5

Hexavalent Chromium

10

2**

Cobalt

none

none

Copper

900

1

Fluoride

none

none

Lead

200

1

Mercury

5

0.2

Molybdenum

100

200

Nickel

1000

20

Selenium

8

0.4

Thallium

2

none

Vanadium

300

20

Zinc

8000

0.4

* Lower value shown in bold

** Same value as proposed TTLC based on human health

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

The second screen involved a consideration of the soluble or extractable fraction of the ten waste constituents. The limiting ecological endpoint for nickel and copper was toxicity to aquatic plants (1). Since the proposed SERTs for these metals are based on Ambient Water Quality Criteria for the protection of aquatic life, the SERTs should protect aquatic plants. Therefore no changes are proposed in the human-health-based exit-level TTLCs for these elements.

Vanadium The limiting ecological endpoint in the HWIR analysis for vanadium was phytotoxicity. Estimated no-effect concentrations range from 2 to 20 mg/kg (1,3). However, these values are below even minimum ambient levels in California and thus cannot be used as the basis for regulatory standards. The STLC is the basis of the the proposed TTLC for vanadium (see page 37).

Cadmium The draft HWIR ecological exit concentration for cadmium, based on toxicity to soil fauna, is 5 mg/kg (1). The lowest Oak Ridge National Laboratory screening concentration of cadmium, based on phytotoxicity, is 3 mg/kg (3). Assuming that the waste is applied to the land at the rate of 7000 kg/ha/year for 20 years as described previously, the maximum cadmium concentration in the waste that would not result in a final soil concentration exceeding the 3 mg/kg screening level for phytotoxicity is 60 mg/kg.

Lead The draft HWIR ecological exit concentration for lead is 1 mg/kg, based on toxicity to soil fauna (1). This value cannot be used as a basis for defining hazardous waste in California, where background soils contain a minimum of 14 times that amount of lead. The ORNL screening concentrations based on phytotoxicity and soil fauna toxicity are 50 and 500 mg/kg, respectively (2,3). Assuming that the waste is applied to the land at the rate of 7000 kg/ha/year for 20 years as described previously, the maximum concentration of lead in the waste that would not result in a final soil concentration exceeding the 50 ppm screening level for phytotoxicity is 990 ppm. Rounded to one significant figure, this results in a suggested exit-level TTLC of 1000 mg/kg.

Zinc The draft HWIR ecological exit concentrations for zinc is 0.4 mg/kg, based on toxicity to soil fauna (1). The ORNL screening levels for zinc are 50 and 100 mg/kg, based on phytotoxicity and soil microorganisms, respectively. These concentrations are well below 90 th percentile background concentrations in the California soils (tab 9), and thus cannot be used as a basis for defining hazardous waste in California. Since no satisfactory criterion is available for total zinc, DTSC proposes to regulate zinc in solid waste only by its soluble or extractable concentration.

Selenium The limiting toxicological endpoint for selenium is reproductive toxicity in waterfowl. The threshold for this endpoint can be estimated in a variety of ways (see Tab 8). The California EPA Office of Environmental Health Hazard Assessment (OEHHA) recommends calculating the endpoint using a benchmark dose and a sediment-fish transfer factor (ranging from 3.9 to 15.6), and assuming 100% foraging on a contaminated site as well as conditions favoring selenium uptake into dietary items of aquatic birds. However, in order to be consistent with the approach used throughout this proposed revision of the waste classification system, the approach of Van Derveer and Canton (Tab 8) was selected as the basis for the proposed lower TTLC for selenium. Those authors determined EC10 values (10th percentile estimates of the threshold for selenium toxicity in sediment) of 2.5 and 4.0 mg/kg, dry weight, associated with predicted and observed effects, respectively, in wild fish and birds. Assuming that the waste is applied to the land at the rate of 7000 kg/ha/year for 20 years as described previously, the maximum selenium concentration in the waste that would not result in a final soil concentration exceeding the 2.5 mg/kg EC10 based on predicted effects for waterfowl toxicity is 50 mg/kg. The proposed ecosystem-based, exit-level TTLC for selenium is therefore 50 mg/kg, dry weight (however, see page 37).

Mercury According to the OEHHA analysis, the limiting pathway for mercury is biomethylation, uptake by benthic organisms, and food web transfer of the organomercury to fish and ultimately to predator fish, mammals, and birds (Tab 8). The belted kingfisher was chosen as the species of

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

concern because it is a sensitive fish-consuming bird, and birds appear to be at least as sensitive to methymercury as fish or mammals. Using the mallard dietary reproductive no-adverse-effect concentration (NOAEL) for rnethylmercury of 0.05 mg/kg diet, with an interspedas conversion factor of 3.2 (reflecting a daily food consumption rate of 15.6% body weight for the mallard versus 50% body weight for the kingfisher), and a conservative assumption of 100% foraging on contaminated fish, a dietary NOAEL for the kingfisher would be 0.05/3.2 = 0.016 mg/kg diet.

In order to relate the mercury concentration in the kingfisher's diet to a concentration in sediment, a sediment-to-fish transfer factor is needed. A range of sediment-to-fish transfer factors identified from the literature for California (0.013–20; Table 1, Tab 4d). Combining these transfer factors with the estimated dietary NOAEL for the kingfisher, an estimated range of maximum "safe" sediment concentrations for the kingfisher would be 0.0008 to 1.2 mg/kg sediment, dry weight. Assuming that the concentration in the sediment is the same as the concentration in the soil (for example, fields to which the waste has been applied may be flooded to form wetlands) and that the waste is applied to the land at the rate of 7000 kg/ha/year for 20 years as described previously, the maximum mercury concentration in the waste that would not result in a final sediment concentration exceeding the 0.0008 to 1.2 mg/kg sediment, dry weight 0.016 mg/kg screening sediment concentration for food-web toxicity is (0.0008 to 1.2) × 19.8 = 0.011 to 17 mg/kg sediment (geometric mean 0.19).

Endrin The HWIR exit concentration for endrin is 0.1, based on toxicity to the great blue heron via the aquatic food web. This concentration was accepted as the eco-based TTLC for endrin because it was verified using the environmental transport modeling of endrin from waste to fish in CalTOX Land Conversion.

Methoxychlor The HWIR exit concentration for methoxychlor is 3, based on toxicity to sediment-dwelling organisms. The HWIR benchmark dose for sediment-dwelling organisms is converted from the ambient water quality criterion for the protection of aquatic life (AWQC) of 0.00003 mg/l, using equilibrium partitioning. This conversion involves the implied assumption that toxicity to benthic organisms can be predicted by pore water concentration in sediment and that these organisms will be protected if pore water concentration does not exceed the AWQC. The same thing is accomplished by limiting the soluble or extractable concentration of endrin in the waste to 100 times the AWQC. The latter is DTSC's proposed approach. Thus, no change is proposed in the human-health-based TTLC of 100.

References

1. U.S. Environmental Protection Agency, 1995, Technical Support Document for the Hazardous Waste Identification Rule: Risk Assessment for Human and Ecological Receptors, Office of Solid Waste Contract # 68-D2-0065, 68-W3-0028.

2. Oak Ridge National Laboratory, undated, Toxicological Benchmarks for Potential Contaminants of Concern for Effects on Soil and Litter Invertebrates and Heterotrophic Process, ES/ER/TM-126/R1.

3. Oak Ridge National Laboratory, 1995, Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Terrestrial Plants: 1995 Revision, ES/ER/TM-85/R2.

4. Wildlife Exposure Factors Handbook. US EPA 1993, EPA/600/R-93/187a Office of Research and Development

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Table 3: Risk-based Candidate TTLCs

 

Upper TTLC (mg/kg)

Lower TTLC(mg/kg)

Chemical

Nearby Residents

Waste workers

LCS Residents

Ecological concerns

Aldrin

0.006

3

0.0009

protectede

Chlordane

1

30

0.06

protectede

DDD

20

200

0.3

protectede

DDE

1

150

0.3

protectede

DDT

4

100

0.7

protectede

2,4-Dichlorophenoxyacetic acidi

3,000

1500

50,000d

protectedf

Dieldrin

0.2

3

0.004

protectede

Endrin

70

150

0.8

0.1

Heptachlor

0.7

6

2d

protectede

Kepone

0.2

3

0.02

protectede

Tetraethyl Lead

8 × 10-6

0.0003

0.0007d

protectedf

Lindane

60

30

5

protectede

Methoxychlor

7,000

2,000

100

6,400

Mirex

0.9

2

0.04

protectedf

Pentachlorophenoli

500

500

400

protectede

Polychlorinated biphenyls (PCBs)a

nd

nd

nd

nd

Tricholoethylene (TCE)

20

70

2,000d

protectede

Toxaphene

0.04

30

6d

protectede

2,4,5-Trichlorophenoxyproprionic acidi

2,000

1000

40,000d

protectede

Vinyl chloride

0.2

0.7

50d

protectedf

2,3,7,8-Tetrachlorodibenzodioxin

7 × 70-7

5 × 10-4

1 × 10-7

protectede

Inorganic lead

20,000

6,000

5,000

1000

Antimony

15,000

700

4,000d

protectede

Arsenic

200

40

400d

protectede

Asbestosb

nd

nd

nd

nd

Barium (excluding barite)

>1,000,000

100,000

700,000d

protectede

Beryllium

300

20

200d

protectede

Cadmium

150

500

3,000

60

Trivalent Chromiumc

>1,000,000

>1,000,000

>1,000,000

protectede

Hexavalent Chromium

5

15

80d

protectedf

Cobalt

15,000

20,000

200,000d

protectede

Copper

>1,000,000

70,000

400,000d

protectedg

Fluoride

>1,000,000

100,000

600,000d

protectede

Ionic Mercury

10,000

500

3,000

0.2

Molybdenum

200,000

9,000

50,000d

protectede

Nickel

3,000

7,000

50,000d

protectedg

Selenium

200,000

9,000

50,000

40

Thallium

3,000

150

800d

protectede

Vanadium

300,000

10,000

70,000

2–20

Zinc

>1,000,000

500,000

>1,000,000d

protectedh

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

a New TTLCs for PCBs have not been determined.

b New TTLCs for asbestos have not been computed.

c For these scenarios, Crill does not pose a health threat.

d The lower TTLC values were greater than the upper TTLC.

e Using the HWIR ratio, the residential TTLC protects ecosystems.

f Chemical not considered by EPA to be a priority for eco-assessment.

g The SERTs protect against toxicity to aquatic plants.

h No acceptable eco-based concentration available. Zinc in waste will be limited by their soluble or extractable fraction only.

i Chemical parameters for the unionized moiety were used.

j Mercury range 0.011–17 with geometric mean of 0.19 mg/kg.(see text)

The spreadsheets named in Table 1 and described in the sections above were used to compute risk-based concentrations for the four scenarios. The results of these computations are presented in the four columns of Table 3. The rows of Table 3 are divided with the organic chemicals (CalTOX) shown in the top half, inorganic lead (Lead spreadsheet) shown as a single line in the center, and other inorganic chemicals (PEA) shown in the bottom half.

The list of chemicals for which TTLCs were computed is based on the list of chemicals for which TTLCs currently exist in regulation. The chemical names in Table 3 differ than those currently appearing in regulation for several chemicals. First, DDE DDT and DDD all appear separately in a box in the table. DDT can be converted into DDE or DDD. Therefore, risk-based TTLC values were computed for all three chemicals. The lowest of the six upper values (DDE-nearby resident) was selected as the risk-based upper-level TTLC. The lowest of the three land conversion residents (DDE) was selected as the lower risk-based TTLC. Second, risk-based computations require that a single chemical with specific chemical and toxicological properties be identified to compute TTLC. This can lead to identifying a single chemical as a surrogate for other similar chemicals. Tetraethyl lead is used as a surrogate for all organic lead. Third, vinyl chloride has been moved from to the list of carcinogens in section 66261.24 of the current regulation to this list because of the importance of this chemical. Fourth, total chromium has been replaced by trivalent chromium. All chromium is either considered trivalent or hexavalent because of the large differences in the toxicity of two valances. Fifth, mercury has been restricted to ionic mercury excluding organic mercury and elemental mercury. Sixth, silver has been eliminated from the list because the form found in the environment is known not to be bioavailable.

There are also several explanations required of values in the Table 3. First, no new TTLCs are being proposed for PCBs or asbestos. Both the analytical methods and toxicity criteria for PCBs are in a state of change currently. Efforts are under way to create a toxicity equivalency factor approach for PCBs similar to dioxin. Therefore the department is waiting for the outcome of these efforts before proposing a new TTLC. Asbestos risks are based on fiber counts. This information has not changed greatly, so an update was deemed unnecessary. Second, the organic acids pentachlorophenol, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyproprionic acid (2,4,5-T) exist in an unionized form at lower pHs. This form is more volatile and less water soluble than the ionized form. Since the objective of the TTLCs is to model the exposure pathways other than those involving ground water, the chemical characteristics of the unionized form were used to predict the fate of these chemicals in the environment. At pH values between 5 and 9, the environmental fate of pentachlorophenol will be well represented by the CalTOX equations; prediction errors are larger for 2,4-D and 2,4,5-T.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
Second Stage: Detection Limits and Ambient Concentrations

Following the calculation of risk-based candidate TTLCs, these values are evaluated to determine whether they can be practically implemented as regulatory limits. First, a policy decision was made not to set any TTLC lower than could be measured, since a toxicity threshold is not a useful criterion if it is so low that it cannot be measured. Second, a policy decision was made not to set any TTLC lower than concentrations which are naturally present in California soils or widely distributed in the environment.

Estimated Quantification Limits

Estimated quantitation limits (EQLs) are defined as the lowest concentration that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions (Tab 5a). The EQL considers the limitations of the analytical method and the effects of processing the sample matrix. The EQL for substances in complex matrices, such as oily sludges, can be quite high. An EQL is calculated for each chemical for each regulatory limit class (upper TTLC, lower TTLC). Each EQL is then multiplied by two because in order to statistically evaluate compliance with a standard, one must be able to measure concentrations above and below the standard.

Risk-based candidate TTLC which were less than twice the EQL were changed to twice the EQL. The proposed upper TTLC for toxaphene and proposed lower TTLCs for chlordane, heptachlor, methoxychlor, toxaphene, Silvex, and vinyl chloride are based on EQLs.

Comparison with Background Concentrations

Inorganics: A two-step process was used to implement the policy decision to consider background concentrations in setting TTLCs for inorganic chemicals:

(1)  

All calculated health-based levels for inorganic chemicals regulated by DTSC (except fluoride and hexavalent chromium), were compared with maximum background levels found in native California soils, as reported in the University of California, Riverside study. The risk-based concentrations for mercury and vanadium were less than their maximum background concentrations.

(2)  

Determine the concentrations of vanadium and mercury in waste that would not cause a significant increase in background concentrations of these substances, when the wastes were mixed with soil as postulated in the land conversion scenario, discussed earlier. The following table shows the calculation steps for vanadium and mercury.

 

UCR soils data

 

USGS soils data

 

average

waste

 

mean

90%

difference

mean

90%

difference

difference

concentration

mercury

0.26

0.612

0.352

0.154

0.47

0.316

0.3342

6.62

vanadium

24.3

185.2

161

124.8

200

75.2

118

2337

A ''significant increase'' was defined as the difference (columns 4 & 7) between the means (columns 2 & 5) and the ninetieth percentiles (columns 3 & 6). This calculation was done for the UCR data (1) and the USGS data (2), and the the results averaged (column 8). Since the land conversion scenario results in a 19.8-fold dilution of the waste as it is mixed with soil, the equivalent waste concentration is 19.8 times this average difference (column 9). This means

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

that if waste containing mercury or vanadium at the concentration in column 9 is mixed with soil that contains average background concentrations of these metals, the resulting mix will contain no more mercury or vanadium than the 90th percentile of background.

Organics: Dioxins and dibenzofurans are generally formed as a result of human activities. As sources of these compounds are brought under control, the levels in the environment are dropping and will probably continue to do so. Published data on the distribution of dioxins in the environment in the U.S. and the U.K. were used to estimate ambient concentrations in soils, which appear to have a mean and standard deviation of approximately 0.000008 mg/kg (TEQ). Second, the concentration of dioxin TEF in waste that would not cause a significant increase in background concentrations of these substances was determined. A 'significant increase' in this case, was defined as an increase of 1.28 standard devations, or 0.00001 mg/kg (TEQ). The concentration in waste that would produce such change in soil, estimated using the land conversion scenario, was 0.0002 mg/kg (0.00001 × 19.8). For each chemical, the value that is the basis for the TTLC is shown in bold in Table 4:

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Table 4: Comparison of Risk-based Levels with Quantitation Limits and Ambient Levels

 

Upper TTLC (mg/kg)

 

Lower TTLC(mg/kg)

 

Chemical

Risk-based Level

Estimated Quantitation Limit

Ambient Level

Risk-based Level

Estimated Quantitation Limit

Ambient Level

Aldrin

0.006

0.68

na

0.0009

0.046

na

Chlordane

1

0.74

na

0.06

0.05

na

DDT & congeners

1

0.5

na

0.3

0.034

na

2.4 D

3000

4

na

noned

 

 

Dieldrin

0.2

0.88

na

0.004

0.059

na

Endrin

70

0.78

na

0.1

0.052

na

Heptachlor

0.7

0.8

na

noned

 

 

Kepone

0.2

40

na

0.02

2.7

na

Organic Lead

8 × 10-6

100

na

8 × 10-6f

10

 

Lindane

30

0.5

na

5

0.034

na

Methoxychlor

2000

1.7

na

100

0.12

na

Mirex

0.9

0.3

na

0.04

0.02

na

Pentachlorophenol

500

1.5

na

400

0.1

na

Polychlorinated biphenylsa

nd

nd

nd

nd

nd

nd

Tricholoethylene (TCE)

20

1.2

na

noned

 

 

Toxaphene

0.04

1.7

na

0.04f

0.1

 

2.4.5-T

2000

1.5

na

noned

 

 

Vinyl chloride

0.2

1.2

na

0.2f

0.01

 

PCDD/PCDF (TEQs)b

7 × 10-7

See commentb

2 × 10-4

1 × 10-7

See commentb

2 × 10-4

Inorganic lead

6000

6

97.1

700

0.6

97.1

Antimony

700

120

1.95

noned

 

 

Arsenic

50

20

11

noned

 

 

Asbestosc

nd

nd

nd

nd

nd

nd

Barium (excluding barite)

100,000

400

1400

noned

 

 

Beryllium

30

10

2.7

noned

 

 

Cadmium

200

10

1.7

40

1

1.7

Hexavalent Chromium

5

2

na

noned

 

 

Cobalt

10,000

100

46.9

noned

 

 

Copper

60,000

50

96.4

noned

 

 

Fluoride

100,000

100

na

noned

 

 

Ionic Mercury

500

0.4

0.54

0.2

0.04

7e

Molybdenum

9,000

100

9.6

noned

 

 

Nickel

3,000

80

509

noned

 

 

Selenium

9,000

10

0.43

40

1

3.3e

Thallium

100

20

36.2

noned

 

 

Vanadium

10,000

100

190

20

10

2000e

Zinc

500,000

40

236

noned

 

 

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

a New TTLCs for PCBs were not determined. See text.

b This is to be applied to dioxin TEQs not a single congener

c New TTLCs for asbestos have not been computed and the existing TTLCs will be used.

d The lower TTLC values were greater than the upper TTLC, therefore, no lower TTLC is proposed for these chemicals.

e The maximum waste concentration based on background considerations.

f These are the upper TTLC values.

Four significant differences can be seen in the chemical names listed in Table 4 as compared with Table 3. (1) The three chemicals DDT, DDE and DDD have been reduced to a single line called DDT and congeners. The lowest risk-based concentration of the three congeners has been selected because DDT can be transformed into DDE or DDD. (2) The criterion for dioxins applies to 11 dioxin congeners, not just to 2,3,7,8 tetrachlorodibenzodioxin. This is based on the toxicity equivalence factors (TEFs) used by US EPA. Therefore, waste being classified according to their content of dioxins will need to be analyzed for these 11 congeners. The 11 TEFs will be used to compute an equivalent concentration of TCDD. (3) tetraethyl lead has been replaced with organic lead because tetraethyl lead was a surrogate for organic lead. (4) Since non-extractable chromium III and zinc were found to pose no significant effect on human health and the environment, the department proposes to regulate those chemicals only by their SERTs.

References

1. Kearney Foundation of Soil Science, Division of Agriculture and Natural Resources, University of California, Riverside, 1996, Background Concentrations of Trace and Major Elements in California Soils.

2. Boerngen, J.G. and H.T. Shacklette (1981) Chemical analysis of soils and other surficial materials of the coterminous United States. Open-file Report 81-197, U.S. Department of Interior, Geological Survey.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Appendix 4. Acute Toxicity Thresholds

Oral LD50

DTSC has developed recommended acute oral toxicity thresholds for hazardous wastes and special wastes. Hazardous wastes would include wastes with an oral LD50 less than 30 mg/kg. Non-hazardous wastes would include those with an oral LD50 exceeding 500 mg/kg. Special wastes would include wastes with oral LD50s between 30 and 500 mg/kg. These thresholds are calculated as follows:

The Hazardous waste threshold is based on an adult exposure scenario because Special Wastes would be accessible to adults but not ordinarily be accessible to children. Adults are assumed to ingest 0.31 mg of waste per kg body weight., The Special waste threshold is based on a child exposure scenario because in order to be unregulated by the Department, wastes should not be an acute toxicity threat to children. Children are assumed to ingest 5 mg of waste per kg body weight.. The waste ingestion rates for adults and children are 90th percentile estimates of inadvertent soil ingestion derived from the CalTOX model. The means (and coefficients of variation) of those distributions are 1.4e-7 (2) and 2.2e-6 (3), respectively. Uncertainty factors of ten to account for the use of laboratory animal toxicity data to predict human toxicity and ten to extrapolate from a lethal concentration to a minimal-effect concentration were multiplied by the waste ingestion rates to arrive at the acute oral toxicity thresholds.

Dermal LD50

DTSC has developed recommended acute dermal toxicity thresholds for hazardous wastes and special wastes. Hazardous wastes would include wastes with a dermal LD50 less than 5500 mg/kg. Non-hazardous wastes would include those with an oral LD50 exceeding 7400 mg/kg. Special wastes would include wastes with oral LD50s between 5500 and 7400 mg/kg. These thresholds are calculated as follows:

The hazardous waste threshold is based on a dermal contact rate of 55 mg of waste per kg body weight per day by an adult, with an uncertainty factor of 100. The special waste threshold is based on a dermal contact rate of 74 mg of waste per kg body weight per day by a child, with an uncertainty factor of 100. The dermal contact rates for adults and children are 90th percentile estimates of inadvertent contamination of skin by waste using exposure parameters from the CalTOX model. The parameters include fraction of skin surface exposed (mean 30%, SD 1%), soil adhesion (mean 0.5 mg/cm2,SD 0.2), and skin surface area (adult mean 0.024 m2/kg, SD 0.001, child mean 0.032 m2/kg, SD 0.003). Uncertainty factors of ten to account for the use of laboratory animal toxicity data to predict human toxicity and ten to extrapolate from a lethal concentration to a minimal-effect concentration were multiplied by the dermal contact rates to arrive at the acute dermal toxicity thresholds.

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

Inhalation LC50

The purpose of the proposed revisions in the acute inhalation toxicity threshold is to take into account potential exposure as well as toxicity. The proposal would subdivide the regulated wastes into two categories based on the severity of the threat in order to avoid over-regulating wastes which have low exposure potential (low volatility and limited respirability). The waste being classified would not need to be tested if standard reference values are are available for its toxic constituents.

Volatiles: In order to account for both a chemical's acute inhalation toxicity and its tendency to vaporize, classification of a waste containing volatile constituents would be based on the ratio of each constituent chemical's vapor pressure (in ppm @ 250 C) to its inhalation LC50 (in ppm). If this ratio exceeds 0.1, the waste containing the chemical would be a special waste. If this ratio exceeds 1, the waste containing the chemical would be a hazardous waste. These ratios must be summed for wastes with multiple volatile chemicals, i.e. σ(VP/LC50) > 0.1 yields a special waste classification and σ(VP/LC50) > 1 yields a hazardous classification. Vapor pressure in mm Hg is converted to vapor pressure in atmospheres by dividing by 760. This, in turn is converted to ppm by multiplying by 1 million. The rationale for the proposed thresholds is as follows:

A chemical's vapor pressure in atmospheres multiplied by 1 million gives its theoretical maximum concentration in a closed space in ppm, i.e. concentration = 106 * Vp (in mm Hg) / 760, which can be simplified to VP / 0.00076. If this concentration exceeds the LC50 for a volatile chemical, then the chemical could form a lethal atmosphere, and is therefore considered a hazardous waste. Similarly, if a chemical's theoretical maximum concentration is one-tenth times its LC50, then it could form an atmosphere one-tenth of its lethal atmosphere even with and would be considered a special under this classification proposal. The table below is used to classify the waste:

Particulates: Classification of a waste based on its particulate constituents would be based on the respirable fraction of the waste (PM10 the fraction with a particle size less than 10 microns) times the sum of the ratios of each chemical's concentration (in mg/kg) in the respirable fraction divided by its inhalation LC50 (in mg/m3). This ratio accounts for the tendency of the chemical to be suspended in the air and for its acute toxicity by inhalation. DTSC proposes to classify a waste as hazardous if the sum of the concentrations of individual chemicals in the respirable fraction of the waste (in mg/kg) divided by their inhalation LC50s (in mg/m3) times the respirable fraction of the waste exceeds 2×106, and to classify a waste as non-hazardous if the concentration of a chemical in the respirable fraction of the waste (in mg/kg) divided by its inhalation LC50 (in mg/m3) is less than 105. The rationale for these thresholds is as follows:

The concentration of a chemical in the waste multiplied by the particulate concentration in the air yields the airborne concentration of the chemical, assuming that the dust is suspended waste. Simplistically, if this airborne concentration exceeds the LC50 of the chemical, then the resulting concentration will be lethal. However not all airborne particles are respirable. If only a fraction of the waste is respirable, the expression must be corrected to account for the fraction of the waste that is respirable (F), and the concentration of the chemical (C) in the respirable fraction (PM10) of the waste must be used in place of the concentration in the waste as a whole. Thus, the expression for the lethal concentration becomes (F * C * PM10 / LC50 > 1). Because the endpoint is 50% lethality, a safety factor of ten is incorporated, making the expression F * C ×

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×

PM10 / LC50 > 0.1. Finally, concentrations of the various toxic constituents in the waste must be added to determine the total toxic effect of the waste, i.e. F * σ(C × PM10 / LC50 > 0.1). The two assumed airborne dust concentrations are based on the OSHA standard for respirable suspended particulates in the workplace (10-6 kg/m3) and the federal ambient air quality standard for PM10 (5 × 10-8 kg/m3). Thus, the exit threshold becomes F * σ(C × 5 × 10-8 / LC50 > 0.1), and the hazardous threshold becomes F * σ(C × 10-6 / LC50 > 0.1). These expressions can be rearranged to give F * σ(C / LC50 > 2 × 106), and F * σ(C × / LC50 > 105), respectively

The following table is used to classify the waste:

Vapor Pressure/LC50 ratio sum

Classification

Concentration/LC50 sum

VP/LC < 0.1

Non-hazardous waste

C/LC50 < 105

0.1 < VP/LC < 1

Special Waste

na

VP/LC > 1

Hazardous Waste

C/LC50 > 105

Aquatic Toxicity

The current system classifies a waste as hazardous if its aquatic LC50 is less than 500 mg/l. DTSC proposes to classify a waste with an LC50 <500 mg/l as a special waste. A concentration of 500 mg/l would be equivalent to 7 tons in a two-acre lake five feet deep with complete mixing, which DTSC considers to be a reasonable worst-case release. As discussed in appendix 2, above, a composite liner meeting RCRA Subtitle D specifications is assumed to reduce leakage from a landfill by 18-fold (tenth percentile estimate). Therefore, the waste could be 18 times as toxic (assuming that fish exposure is directly proportional to flow rate) without causing toxic effects on fish if it is placed in a subtitle D landfill. Therefore the proposed threshold for the fully hazardous tier is 500/18 = 30, i.e. a waste with an LC50 <30 mg/l would be classified as a hazardous waste

Suggested Citation:"Appendix D: Letter of Introduction, Overview, Concept Paper, and Appendices 1-4 from DTSC Report." National Research Council. 1999. Risk-Based Waste Classification in California. Washington, DC: The National Academies Press. doi: 10.17226/9466.
×
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Risk-Based Waste Classification in California Get This Book
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The Department of Toxic Substances Control (DTSC) of the State of California Environmental Protection Agency is in the process of complying with the Regulatory Structure Update. The Regulatory Structure Update is a comprehensive review and refocusing of California's system for identifying and regulating management of hazardous wastes. As part of this effort, the DTSC proposes to change its current waste classification system that categorizes wastes as hazardous or nonhazardous based on their toxicity. Under the proposed system there would be two risk-based thresholds rather than the single toxicity threshold currently used to distinguish between the wastes. Wastes that contain specific chemicals at concentrations that exceed the upper threshold will be designated as hazardous; those below the lower threshold will be nonhazardous; and those with chemical concentrations between the two thresholds will be "special" wastes and subject to variances for management and disposal. The proposed DTSC system combines toxicity information with short or long-term exposure information to determine the risks associated with the chemicals.

Under section 57004 of the California Health and Safety Code, the scientific basis of the proposed waste classification system is subject to external scientific peer review by the National Academy of Sciences, the University of California, or other similar institution of higher learning or group of scientists. This report addresses that regulatory requirement.

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