Biosolids Applied to Land Advancing Standards and Practices (2002) / Chapter Skim
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4 Advances in Risk Assessment since the Establishment of the Part 503 Rule
4 Advances in Risk Assessment since the Establishment of the Part 503 Rule
Pages 126-163
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From page 126... ...
was established in 1993 (40 CFR Part 503~. It focuses on the changing priorities of cancer versus noncancer end points, acute versus chronic end points, probabilistic risk-assessment approaches, and the need to address aggregate exposures and cumulative risk.
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From page 127... ...
As applied to toxic agents, risk characterization has Eve principal elements:~1) quantification of sources and environmental concentrations in exposure media; (2)
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From page 128... ...
Each of the major steps in this process involves one or more actions that are listed to the right of each major step. Confronting Uncertainty and Variability An important and often ignored final step in the risk characterization process is the characterization of uncertainties.
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From page 129... ...
129 in a)
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From page 130... ...
This report made seventy-f~ve specific recommendations, but among its overarching recommendations are those to address explicitly uncertainty and variability in risk assessment, to address multimedia exposures and cumulaitve intake through multiple exposure pathways, to and foster more interaciion among risk assessors and risk managers. The second report, titled U7zderstat~dir~g Risk, Informing Decisions in a Democratic Society (NRC 1996)
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From page 131... ...
EPA's proposed guidelines for carcinogen risk assessment put more emphasis on "margin of exposure" (relative to a benchmark dose) , weight of evidence, and the use of uncertainty factors in the risk characterization process.
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From page 132... ...
Figure 4-2 provides a time line showing when a number of significant riskguidance documents have been issued relative to the year when the Part 503 rule was issued. Advances in Hazard Identification Since EPA issued cancer and mutagenicity risk-assessment guidelines in 1986 (EPA 1986a,c)
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From page 134... ...
to characterize risk for both carcinogens and noncarcinogens. MOE is the ratio of a dose derived from a tumor bioassay, epidemiologic study, or biologic marker study to an actual or projected human exposure.
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, and meta-analysis. EPA's Proposed 1996 Carcinogen Risk-Assessment Guidelines In 1996, EPA issued its proposed G~idelinesfor Carcz~oger~ Risk Assessment (EPA 1996a)
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From page 136... ...
Only three descriptors for classifying human carcinogenic potential are now available known/likely, cannot be determined, and not likely. · In contrast to the 1986 guidelines that provide very little guidance for risk characterization, the 1996 guidelines provide direction on how the overall conclusion and the confidence of risk are presented for the risk manager and call for assumptions and uncertainties to be clearly explained.
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From page 137... ...
The areas judged to have the most signiftcant opportunities include estimating exposure-response functions; inferring causality, especially when interpreting results of epidemiological studies; and performing complex exposure assessments. Use of Meta-Analysis in Place of Single-Species Data Sets In the evaluation of chemical compounds for carcinogenic risk, regulatory agencies have traditionally fit a low-dose linear dose-response model to data from rodent bioassays.
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From page 138... ...
issued a revised guidance document for chemical mixtures as a supplement to the original guidelines of 1986. The document Supplemental Guidance for Conducting Health Risk ~4~essmet?
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From page 139... ...
; a movement away from simple bounding estimates to probabilistic assessments that include explicit treatment of uncertainty and variability; and the use of multimedia and multiple-pathway exposure assessments. In the sections below, the committee highlights the changes in exposure assessment methods that have particular relevance to biosolids risk assessments.
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From page 140... ...
Explicit Treatment of Uncertainty and Variability Estimating potential human exposures and source-to-dose relationships for harmful substances in biosolids involves the use of models and large amounts of data. Because these data and models must be used to predict individual behaviors, engineered system performance, contaminant transport, human contact and uptake, and dose among large and often heterogeneous
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The recent Exposure Factors Handbook SPA 1997a) , the Monte Carlo guidance document (EPA 1997b)
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In making revisions to the biosolids risk assessment, EPA must strike a balance between expending resources to carry out site-specif~c data collection and expending resources to model and assess risk using existing information. Multimedia and Multiple-Pathway Exposure Assessments Efforts to assess human exposure to contaminants from multiple environmental media have been evolving over the past several decades.
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From page 143... ...
Challenges to the Risk-Characterization Process for Biosolids The emphasis here is on how the process of risk characterization is changing and how those changes impact the Part 503 rule. Particular challenges to the risk-characterization process are to better link risk assessment to risk management, consider risk perception and risk valuation more explicitly, and provide better risk communication between risk assessors and affected populations.
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From page 144... ...
The report also emphasized the need for more research to support children's risk assessments. Children are considered a special subpopulation because their health risks can differ from those of adults because of their immature physiology, metabolism, and differing levels of exposure due to factors such as greater food consumption per unit of body weight and outdoor play activities.
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From page 145... ...
, provides information to improve community involvement in the Superband risk-assessment process. Specifically, this document iden~af~es where community input can augment and improve EPA's estimates of exposure and risk and illustrates why community involvement is valuable during the human health risk-assessment process.
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From page 146... ...
The risk assessment for the Part 503 rule included the assumption that specific management practices are followed. However, because the rule does not explicitly require some of these practices, it is difficult to confirm the extent to which site operators employ these management practices.
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CHANGES IN RISK-ASSESSMENT APPROACHES IN EPA OFFICES A number of EPA offices and programs are involved in developing riskassessment protocols for chemical releases to ambient air, indoor air, surface water, soil, and groundwater. The methods developed in these programs and the evolution of risk-assessment methods within these offices and programs over the past 10 years provide benchmarks against which the relevance and reliability of the Part 503 rule risk assessments can be evaluated.
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From page 148... ...
, conducts assessment of contaminants and sites of national significance, and provides guidance and support to risk assessors. Two major program areas with important developments since the risk assessments were conducted for the Part 503 rule are exposure assessment and cancer assessment.
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From page 149... ...
This example also illustrates the need for conducting multimedia and multiple-pathway exposure assessments. Cancer Risk A~essme';t In 1996, NCEA proposed a revision to the 1986 EPA G~ideli7'e~forCarcinogen Risk~essme7'tto reflect new developments in understanding carcinogenesis (EPA 1996a)
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Another survey that was undertaken is the National Human Exposure Assessment Survey (NHEXAS)
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From page 151... ...
Of particular interest for considering applications of risk-assessment policy are the Radiation Protection Division, Indoor Air Quality Programs, and the Office of Air Quality Planning and Standards within OAR. Radiation Protection Division The Radiation Protection Programs within the Radiation Protection Division provide the methods and scientific basis for EPA's radiation exposure, dose, and risk assessments.
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From page 152... ...
Of particular interest in risk assessment is the OAQPS effort to develop methods to assess human exposure and health risks for particulate matter (PM) and multimedia pollutants released in urban air sheds.
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From page 153... ...
Limits are set through a risk-assessment process that identifies and evaluates multiple exposure pathways. OSW has identified a number of potential exposure pathways linked to landfills and uses multimedia risk assessments to link human exposure and health risk to chemicals in the landfill waste.
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From page 154... ...
Specifically, the supplement suggests ways for Superfund staff and community members to work together during the early stages of Superfund cleanup; identifies where community input can augment and improve EPA's estimates of exposure and risk; recommends questions that the site team should ask the community; and illustrates why community involvement is valuable during the human health risk assessment at Superfund sites. A review draft of Part E provides dermal risk assessment guidance (EPA 2001a)
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From page 155... ...
It is important to provide protection from these microbial pathogens while ensuring decreasing health risks to the population from disinfection by-products. As part of its effort to protect watersheds, OW has established the total maximum daily load IDLE program.
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From page 156... ...
The committee found that the development of methods in the broader academic community and the evolution of risk-assessment methods within various EPA offices and programs provide important benchmarks for the committee's assessment of the relevance and reliability of the Part 503 rule risk assessments. Of particular note are updates to the risk-assessment framework recommended by the NRC, the Presidential/Congressional Commission on Risk Assessment, and various EPA offices.
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From page 157... ...
In particular, improved exposure assessments have led to better exposure classification in health-effects studies. Better descriptions of risk are available, using benchmark dose and margin of exposure to communicate hazard and risk in place of risk of death, hazard quotients, or exposure-potency product relationships.
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From page 158... ...
1986b. Guidelines for the Health Risk Assessment of Chemical Mixtures.
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1992b. Dermal Exposure Assessment: Principles and Applications.
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1998b. Methodology for Assessing Health Risks Associated with Multiple Pathways of Exposure to Combustor Emissions.
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2000d. Strategic Plan for the Analysis of the National Human Exposure Assessment Survey (NHEXAS)
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1997. Framework for Environmental Health Risk Management, Final Report, Vol.
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1993. A decade of studies of human exposure: What have we learned?
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