4
Past and Future Strategies for Sorting and Ranking Chemicals: Applications to the 1998 Drinking Water Contaminant Candidate List Chemicals

John D. Walker, D. Anthony Gray, and Michelle K. Pepling

The 1998 Drinking Water Contaminant Candidate List (CCL) includes chemicals, chemical classes, and microorganisms. This paper discusses only chemicals and chemical classes. However, the strategies for sorting and ranking drinking water contaminant chemicals and chemical classes discussed here are probably applicable to and should be considered for sorting and ranking other types of chemicals as well as drinking water contaminant microorganisms.

EPA'S Responsibilities

Under the August 1996 Amendments to the Safe Drinking Water Act (SDWA), the U.S. Environmental Protection Agency (EPA) must publish the CCL in February 1998 and every five years thereafter, develop the National Drinking Water Contaminant Occurrence Database (NCOD) in August 1999, publish the Unregulated Contaminant Monitoring Regulation List (UCMR) in August 1999 and every five years thereafter, and identify five drinking water contaminants for potential regulation by August 2001 and every five years thereafter.

The EPA published the Draft CCL on October 6, 1997 (EPA, 1997a). After soliciting public comment on the proposed list as mandated under Section 1412(b)(1) of the SDWA, the EPA published the 1998 CCL on March 2, 1998

Under the 1996 Amendments to the SDWA, the EPA must also consider whether drinking water contaminant chemicals should be screened for endocrine disruption potential. As a result, the 206 chemicals with Chemical Abstract Service (CAS) Registry numbers that were on the Draft CCL were included in the Endocrine Disruptor Priority Setting Database (Walker et al., 1999). During development of the Endocrine Disruptor Priority Setting Database, the strengths and weaknesses of the Draft CCL were proposed strength—prepared by screening many sources of chemicals that were likely to contaminate public drinking water systems; weaknesses-concentrations, frequencies of occurrence, and locations of contaminants were not provided, and there were uncertainties concerning the probabilities that proposed contaminants could persist in drinking water. These weaknesses are likely to be addressed as EPA develops the NCOD in August 1999 and publishes the UCMR in August 1999 and every five years



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--> 4 Past and Future Strategies for Sorting and Ranking Chemicals: Applications to the 1998 Drinking Water Contaminant Candidate List Chemicals John D. Walker, D. Anthony Gray, and Michelle K. Pepling The 1998 Drinking Water Contaminant Candidate List (CCL) includes chemicals, chemical classes, and microorganisms. This paper discusses only chemicals and chemical classes. However, the strategies for sorting and ranking drinking water contaminant chemicals and chemical classes discussed here are probably applicable to and should be considered for sorting and ranking other types of chemicals as well as drinking water contaminant microorganisms. EPA'S Responsibilities Under the August 1996 Amendments to the Safe Drinking Water Act (SDWA), the U.S. Environmental Protection Agency (EPA) must publish the CCL in February 1998 and every five years thereafter, develop the National Drinking Water Contaminant Occurrence Database (NCOD) in August 1999, publish the Unregulated Contaminant Monitoring Regulation List (UCMR) in August 1999 and every five years thereafter, and identify five drinking water contaminants for potential regulation by August 2001 and every five years thereafter. The EPA published the Draft CCL on October 6, 1997 (EPA, 1997a). After soliciting public comment on the proposed list as mandated under Section 1412(b)(1) of the SDWA, the EPA published the 1998 CCL on March 2, 1998 Under the 1996 Amendments to the SDWA, the EPA must also consider whether drinking water contaminant chemicals should be screened for endocrine disruption potential. As a result, the 206 chemicals with Chemical Abstract Service (CAS) Registry numbers that were on the Draft CCL were included in the Endocrine Disruptor Priority Setting Database (Walker et al., 1999). During development of the Endocrine Disruptor Priority Setting Database, the strengths and weaknesses of the Draft CCL were proposed strength—prepared by screening many sources of chemicals that were likely to contaminate public drinking water systems; weaknesses-concentrations, frequencies of occurrence, and locations of contaminants were not provided, and there were uncertainties concerning the probabilities that proposed contaminants could persist in drinking water. These weaknesses are likely to be addressed as EPA develops the NCOD in August 1999 and publishes the UCMR in August 1999 and every five years

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--> thereafter. In the interim the EPA asked the National Research Council to establish a Committee on Drinking Water Contaminants. Committee on Drinking Water Contaminants The Committee on Drinking Water Contaminants was asked to assist the EPA with three tasks: (1) developing a scientifically sound approach for deciding whether or not to regulate contaminants on the current and future CCL(s), (2) convening a workshop that will focus on emerging drinking water contaminants and the database that should be created to support future decision making on such contaminants, and (3) creating a scientifically sound approach for developing future CCLs. As part of its effort to assist the EPA with these tasks, the Committee on Drinking Water Contaminants issued a report entitled, Setting Priorities for Drinking Water Contaminants (NRC, 1999). That report described the committee's review of 10 existing prioritization schemes, review of methods for assessing microbial pathogens, approaches used to develop the 1998 CCL, and suggestions for selecting candidates on the CCL for future action. The committee concluded that processes that rank contaminants are not appropriate for selecting regulatory candidates, contaminants occurring at frequencies and concentrations that cause health effects should be regulated, and processes that rank contaminants may be useful to sort and select future contaminants. In their discussion of processes for ranking contaminants, the committee recommended that professional judgments be used to select regulatory candidates. In addition, the Committee on Drinking Water Contaminants suggested that drinking water contaminants could be organized into four categories: Category 1, Ready for Rule-Making; Category 2, Ready for Guidance Development (e.g., health advisories); Category 3, Needing Additional Occurrence Data; and Category 4, Needing Additional Research (e.g., health effects). The committee recognized that, as expected, the quantity and quality of information would be different for each drinking water contaminant and based its categorization criteria on that premise. The committee also recommended a staged process for assessing drinking water contaminants: Stage 1, review existing data (health effects, exposure, treatment, analytical methods); Stage 2, conduct preliminary risk assessment; Stage 3, prepare decision document (regulation, drop, additional research); and Stage 4, prepare data development plan to meet five-year SDWA Requirements. Stages 1 through 3 of the committee's process for assessing drinking water contaminants could be used to assign contaminants to one of the four categories listed above. The review of existing data is more extensive than ordinarily required to categorize chemicals because options for treatment must be considered as well as analytical methods for measuring contaminants in drinking water. The preliminary risk assessment recommended by the committee is analogous to that conducted by the EPA for the premanufacture of new chemicals under the Toxic Substances Control Act (i.e., a 90-day process that uses models to estimate exposure potential and structure activity relationships (SARs) and quantitative structure activity relationships (QSARs) to predict toxicity). The

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--> decision document is necessary to assure a consistent decision-making process. The need to prepare a data development plan is critical to publishing the CCL, publishing the UCMR List, and identifying five drinking water contaminants for potential regulation every five years to meet the statutory deadlines of the 1996 amendments to the SDWA. Past Techniques for Prioritizing Chemicals With very few exceptions, there are two major differences between past techniques for prioritizing chemicals and those currently being developed for future use: (1) past techniques did not have distinct sorting and ranking phases and (2) past techniques were not peer-reviewed or published in peer reviewed journals or books. The exception to those that did not have distinct sorting and ranking phases and have not been published in peer reviewed journals or books were those developed by and for the Toxic Substances Control Act (TSCA) Interagency Testing Committee (ITC) (Welsh and Ross, 1982; Walker, 1993a). The exception to those that have not been peer-reviewed are those that have been proposed for public comment (e.g., those developed for the ITC, the Agency for Toxic Substances and Disease Registry, the EPA's Office of Solid Waste, and California's Office of Environmental Health Hazard Assessment). The techniques developed by and for the ITC were the first techniques used by the U.S. government to sort and rank chemicals (Davis et al., 1997). Sequential sorting and ranking are critical because they promote simultaneous allocation of resources to highest-ranking chemicals within classes that have been sorted based on chemical structure or categories that have been sorted based on uses, human exposures, environmental releases, environmental fate parameters, health or ecological effects, and so forth. Peer review is significant because it provides credibility to the chemical sorting and ranking process. Techniques Reviewed by the Committee on Drinking Water Contaminants The Committee on Drinking Water Contaminants reviewed 10 existing chemical prioritization schemes and considered their relevance for developing a prioritization scheme for drinking water contaminants (NRC, 1999). Three prioritization schemes were developed by private organizations for drinking water contaminants. Three schemes were developed by federal and state organizations to prioritize all contaminants. Four schemes were developed by federal organizations to prioritize contaminants for specific media.

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--> Schemes to Prioritize Drinking Water Contaminants The first prioritization scheme for drinking water contaminants was initiated by compiling a list of chemicals from a few of the sources proposed by the EPA (1997a). This scheme provided a risk index score based on four weighted criteria: production quantity, exposure quantity, occurrence in water, and human health effects. If one criterion was missing, the chemical was not scored. The second scheme provided a sequential prioritization process for health effects, exposure potential, controlling release and treatment technology. No chemicals were evaluated using this scheme, which apparently does not exclude a chemical if all data were not available. The third scheme for drinking water contaminants was not used to evaluate any chemicals but would exclude a chemical if all data were not available (NRC, 1999). Schemes to Prioritize All Contaminants The first prioritization scheme for all contaminants was used to screen a number of chemicals and provided a chemical score based on toxicity (human health or ecological effects), persistence, bioaccumulation, and mass of the contaminant in waste streams. The second prioritization scheme was used to sort chemicals by chemical substructure and associated health or ecological effects as provided by expert opinions; exposure and toxicity could be scored by using empirical data or predictions, including SARs or QSARs, and a need for data by a U.S. government organization(s) could be factored into the weighting criteria. The third scheme uses toxicity information and expert opinion to assign priorities and exposure information to determine the order in which priority toxic chemicals are assessed (NRC, 1999). Schemes to Prioritize Contaminants for Specific Media The first scheme to prioritize contaminants for specific media ranks hazardous waste sites and is relevant to setting priorities for drinking water contaminants, because the contaminants at the hazardous waste sites determine the potential to cause adverse effects to human health or the environment. The second scheme ranks hazardous waste sites and the contaminants at hazardous waste sites for potential to cause adverse human health effects. The third scheme to prioritize contaminants for specific media is used to indicate sediment contamination potential. The fourth scheme is used to estimate the potential for pesticides applied to apples and potatoes to contaminate groundwater (NRC, 1999). Other Techniques There are two other techniques for ranking chemicals that may be relevant to developing a prioritization scheme for drinking water contaminants. The Michigan Critical Materials Register ranks chemicals that may threaten water quality in

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--> Michigan. The Ontario Ministry of the Environment Scoring System ranks chemicals that may threaten surface water quality in Ontario. Both of these techniques have been described by Davis et al. (1997). Future Procedures for Sorting and Ranking Chemicals Future procedures for sorting and ranking chemicals must consider the continued resource and testing facility limitations for assessing the risks of chemicals, promoting pollution prevention and so forth. Strategic planning will be required to assure that these resources are effectively allocated. Formulation of strategic plan should involve development of a scheme that considers vital information and facilitates sorting and ranking of chemicals into phased programs that can be accomplished with the given resources. A scheme that considers vital information and facilitates sorting and ranking of chemicals into phased data collection and testing programs is illustrated in Figure 4-1. This scheme to sort and rank structural classes of chemicals for data collection, testing, and risk assessment includes: a process to organize chemicals into structural classes; a review of existing data and predictions for structural classes of chemicals; consideration of legal (e.g., statutory-mandated) requirements; development of a relational database, consisting of exposure, effects, fate and other compartments, chemicals sorted into categories within each compartment (e.g., within the effects compartment, there may be chemicals sorted into carcinogenicity, acute toxicity, aquatic toxicity categories, etc.), and chemicals ranked (when possible) within each category (e.g., within the aquatic toxicity category, chemicals could be ranked on fish LC50 values, aquatic invertebrate EC50 values, etc.); use of the relational database to produce output scenarios (e.g., chemicals with annual production volumes exceeding a certain threshold that have been measured in surface waters (the concentration of which is given) and that are toxic to fish (the LC50 values are given) that can be used with professional judgments to sort chemicals into groups for which (1) no additional data are needed at that time (defer), (2) more data need to be obtained, (3) testing (including screening tests) should be conducted or, (4) risk should be assessed); a phased short- and long-term program to which highest-ranking chemicals (from database categories of ranked chemicals and professional judgments) within groups needing data or testing are assigned to the first phases of data collection or testing; processes that assure that results from phased data collections and testing are reviewed and decisions to defer, test, or assess risk are made; and feedback loops that provide pathways for phased testing data to be (a) used for development and validation of SAPs and QSARs, (b) incorporated into risk assessments and (c) included in future data assessments of structurally related chemicals.

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--> 1998 Drinking Water Contaminant Candidate List The 1998 Drinking Water Contaminant Candidate List consists of 48 chemicals with unique Chemical Abstract Service Registry numbers and chemical structures (See Table 4-1). There are 20 industrial organic chemicals, 22 pesticides, and six inorganic chemicals on the list. TSCA Interagency Testing Committee (ITC) The ITC is an independent advisory committee to the EPA administrator that was created in 1976 under Section 4(e) of the TSCA. Sixteen U.S. government organizations are ITC members: the Agency for Toxic Substances and Disease Registry (ATSDR), the Council on Environmental Quality (CEQ), the Consumer Product Safety Commission (CPSC), the U.S. Department of Agriculture (USDA), the U.S. Department of Commerce (DOC), the U.S. Department of Defense (DOD), Food and Drug Administration (FDA), the U.S. Department of the Interior (DOI), the U.S. Environmental Protection Agency (EPA), the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences (NIEHS), the National Institute for Occupational Safety and Health (NIOSH), the National Library of Medicine (NLM), the National Science Foundation (NSF), the National Toxicology Program (NTP) and the Occupational Safety and Health Administration (OSHA). Members from these U.S. government organizations nominate industrial chemicals to the ITC when their organizations need data that can be obtained through the ITC. These data include unpublished production volume, use, exposure, monitoring, environmental fate, ecological effects, and health effects data. The ITC coordinates data needs for the nominated chemicals with those of other member organizations and determines if these chemicals should be (1) added to the Priority Testing List and recommended or designated for testing, (2) deferred for testing and not added to the list or (3) removed from the list. The ITC meets monthly to identify and coordinate federal data needs for industrial chemicals, recommends these chemicals in Federal Register Reports to the administrator every May and November, and establishes partnerships with manufacturers, importers, processors, and users of recommended chemicals to discuss data needed. By coordinating federal data needs and establishing partnerships, the ITC provides an infrastructure to obtain information on industrial chemicals (http://www.epa.gov/opptintr/itc/). ITC Decisions for the 1998 CCL Chemicals The ITC has made testing decisions on about 40,000 chemicals (Walker, 1993a). The ITC has deferred testing on 1998 CCL chemicals that are only used as pesticides because chemicals that are registered active pesticide ingredients are regulated under the Federal Insecticide Fungicide Rodenticide Act, not TSCA (See Table 4-2). However, the ITC does review data on pesticides to facilitate

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--> toxicity and persistence predictions for structurally related industrial chemicals and to develop SARs and QSARs. Eleven of the 1998 CCL chemicals were recommended for testing by the ITC in Federal Register reports to the EPA administrator (Table 4-2). Eight of the recommended 1998 CCL chemicals have been removed from the Priority Testing List because the EPA implemented the ITC's testing recommendations (Table 4-2). As result of the ITC's recommendations and EPA's implementation of the ITC's testing recommendations, many of the 1998 CCL chemicals recommended for testing by the ITC are well-characterized industrial chemicals. The most well-known 1998 CCL chemical recommended by the ITC is probably methyl-tert butyl ether (MTBE), because it was recommended by the ITC before it was commercially significant and at a time in the commercial life cycle of the chemical when it was easiest to request voluntary development of test data (Walker, 1993b). TSCA Section 4 and 8(d) Studies Indexed in the TSCA Test Submissions (TSCATS) Database As a result of ITC recommendations and related EPA actions, over 1,300 unpublished studies have been submitted to the EPA for the 1998 CCL chemicals (See Table 4-3). These studies are indexed in the TSCATS database. For each study there is a reference in TSCATS, and the reference may be a document that contains more than one study, explaining why the number of studies in Table 4-3 is equal to or greater than the number of references. Procedures for retrieving studies indexed in TSCATS were recently published (Walker and Smock, 1995). TSCATS is a pointer system—that is, it is a database that points to unpublished studies that have been submitted to EPA under TSCA. It can be accessed through the World Wide Web from the following universal resource locators: (url) http://www.rtk.net or http://igm.nlm.nih.gov/. From the Right-To-Know (RTK) page the user must search on databases. From the NLM page the user must select TOXLINE and then, under the "Apply Limits" section, choose "Toxic Substances Control Act Test Submissions." When the EPA publishes a Federal Register notice under TSCA Section 4(a), manufacturers and processors of chemicals mentioned in that notice can provide TSCA Section 4(a) studies to reduce the possibility of having to conduct tests under a TSCA Section 4(a) rule or they can provide TSCA Section 4(d) studies that were conducted as a result of testing to meet the requirements of a TSCA Section 4(a) notice. The total number of TSCA Section 4 studies listed in Table 4-3 includes both TSCA Section 4(a) and 4(d) studies. When the ITC adds a chemical to the Priority Testing List, the EPA automatically promulgates a TSCA Section 8(d) Health and Safety Data Rule. This rule requires manufacturers and processors of chemicals recommended by the ITC to submit unpublished health and safety studies (health effects, environmental fate, ecological effects, environmental and occupational monitoring, industrial hygiene, etc.) to the EPA. By comparing the chemicals recommended or designated by the ITC (Table 4-2) with the number of TSCA

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--> Section 8(d) studies for 1998 CCL chemicals (Table 4-3), it is obvious that there are some chemicals that were deferred by the ITC for which a number of TSCA Section 8(d) studies have been submitted to the EPA. There are two explanations for this: (1) EPA published a TSCA Section 8(d) rule for chemicals other than those recommended by the ITC or (2) when manufacturers and processors submitted documents (references) in response to a TSCA Section 8(d) rule, the documents contained studies on other chemicals that were not subject to the rule. The ITC encourages manufacturers and processors of ITC-recommended chemicals to submit these and other studies electronically through the Voluntary Information Submission Innovative Online Network (VISION; http://www.epa.gov/opptintr/itc/vision/). Uses and Substructure-Based Computerized Chemical Selection Expert System (SuCCSES) Chemical Classes for the 1998 CCL Chemicals Uses were identified for the 1998 CCL chemicals; most are used as herbicides or insecticides (See Table 4-4). Identifying uses is important because it promotes pollution prevention through the recognition that less toxic and less persistent chemicals can be substituted for more toxic and more persistent chemicals with similar uses. SuCCSES is the first computerized system that uses expert opinions to predict potential environmental-human health interactions of individual chemicals and chemical classes that share common substructures (Walker, 1995a; Walker and Gray, 1999). For chemical categories in SuCCSES, expert opinions were offered on the potential of chemicals containing specific substructures to cause adverse human health effects or to cause effects on the environment by adversely affecting ecologically diverse classes of organisms. SuCCSES contains over 100 chemical substructures associated with about 10,000 chemicals. Effects on human health indicated potential for chemicals containing one or more of these substructures to cause acute, chronic, mutagenic, oncogenic, developmental, reproductive, or neurotoxic effects or membrane irritation (Walker, 1991, 1995a). Effects on the environment included predictions on chemicals containing one or more of these substructures to potentially cause adverse effects to algae, aquatic invertebrates, birds, fish, mammals, microorganisms, plants, or terrestrial invertebrates (Walker and Bink, 1989; Walker, 1991). Using SuCCSES it was possible to assign the 1998 CCL chemicals to one of 17 SuCCSES classes (Table 4-4). Organizing chemicals into SuCCSES classes is critical for estimating potential health or ecological effects of structurally related chemicals and developing or validating SARs and QSARs.

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--> Log Octanol Water Partition Coefficient (log Kow) Values, Soil or Sediment Sorption Coefficient (Koc) Values, and Henry's Law Constant for 1998 CCL Chemicals The log Kow values, Koc values and Henry's Law constants for the 1998 CCL chemicals (arranged by SuCCSES class) are listed in Table 4-5. These three environmental fate parameters were selected to estimate the potential of chemicals to remain in drinking water. These parameters can be used when reservoirs (containing aquatic species that can bioconcentrate chemicals and sediment to which chemicals can sorb) are the source of drinking water. For other drinking water sources, different parameters may have to be used. Using previously described criteria for log Kow values, Koc values, and Henry's Law constants it was possible to estimate the potential of chemicals to bioconcentrate, sorb to sediment or soil, and evaporate from water, respectively (Walker, 1995b). These criteria are listed below: log Kow Bioconcentration Potential Koc Sorption Potential Henry's Law Constant (atm m3/mole) Evaporation Potential <3 Low <2,700 Low >10-2 High 3-8 Moderate to High >2,700 High 10-2- 10-7 Moderate >8 Low     <10-7 Low By organizing the 1998 CCL chemicals into SuCCSES classes (number of chemicals in each class in parentheses), it was possible to estimate the potential of chemicals within these classes to remain in reservoirs of drinking water: High potential to remain in reservoir water (low bioconcentration, sorption, and evaporation potential): acetanilides (2), phenols (2), triazines (7), and ureas (2). Moderate potential to remain in reservoir water (moderate bioconcentration, sorption, or evaporation potential): aliphatic halides (8) (aldrin, dieldrin, and hexachlorobutadiene may bioconcentrate or sorb to soil or sediment); aromatic halides (4) (DDE may bioconcentrate or sorb to soil or sediment); aromatic hydrocarbons (2); carbamic acid esters (1); ethers (1); halophenols (2); hydrazines (1); nitroaromatics (3); phosphonothioates (1); phosphorodithioates (2); and phosphorothioates (1). Low potential to remain in reservoir water (low bioconcentration and sorption potential but high evaporation potential): aliphatic halides (2) (1,1-dichloropropene and 2,2-dichloropropane); aromatic hydrocarbons (1) (p-isopropyltoluene).

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--> Log Kow, Koc, and Henry's Law constants may be used to estimate the potential of chemicals and chemical classes to remain in drinking water. However, some professional judgment should be used before these chemicals or chemical classes are sorted or ranked (Figure 4-1). Professional judgment would consider other environmental fate parameters that could affect the ability of some chemicals or chemical classes to remain in drinking water (e.g., hydrolysis of carbamic acid esters, hydrazines). Application Of Past Chemical Sorting Techniques To The 1998 Ccl Chemicals As noted earlier, almost all past techniques did not have distinct sorting and ranking phases. However, a few techniques developed in the recent past do promote sorting (e.g., the Use Cluster Scoring System, SuCCSES, and the Endocrine Disruption Priority Setting Database (EDPSD). The Use Cluster Scoring System can be used to sort chemicals into use categories (Davis et al., 1997). SuCCSES was described earlier. The EDPSD can be used to sort chemicals into structural classes and categories based on uses, production volumes, environmental fate parameters, occurrences in fish and wildlife tissues, reproductive effects, estrogen receptor binding affinity potentials, and so on (Walker et al., 1999). Past sorting techniques (uses and environmental fate parameters) were applied to the 1998 CCL chemicals; the results are summarized in Table 4-5 and discussed earlier. Application Of Past Chemical Ranking Techniques To The 1998 Ccl Chemicals To illustrate the application of past ranking techniques, the aliphatic halides from Table 4-5 were ranked based on exposure and effects scores developed by and for the ITC (Walker, 1993b, 1995a). Exposure Scores Exposure scores and criteria for assigning scores to exposure factors that were relevant to ranking aliphatic halides are production volume, environmental persistence, and bioaccnmulation potential (See Table 4-6). These scores and criteria were applied to the aliphatic halides from the 1998 CCL (See Table 4-7). Ranking on production volume indicated that there were three groups of aliphatic halides: those with annual production volumes greater than 10 million pounds, greater than 1 million pounds, or less than 1 million pounds (Table 4-7). Ranking on environmental persistence indicated that there were two groups of aliphatic halides: those that could persist for years and those that could persist for months (Table 4-7). Ranking on bioaccumulation potential indicated that there were three groups of aliphatic halides based on based on log Kow (Table 4-7). The three aliphatic halides that could persist for years (aldrin, dieldrin, and

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--> hexachlorobutadiene) were the same three that could bioconcentrate or sorb to soil or sediment (Table 4-5). Effects Scores Four biological effects that were relevant to ranking the 1998 CCL chemicals were acute toxicity, mutagenicity, carcinogenicity, and ecotoxicity (See Table 4-8). The scores and criteria for these biological effects were applied to the aliphatic halides from the 1998 CCL (See Table 4-9). Positive scores (based on empirical data) and negative scores (based on predictions) for biological effects were evaluated separately. Based on acute toxicity and ecotoxicity scores, aldrin and dieldrin would rank the highest and 1,1-dichloropropene and 2,2-dichloropropane the lowest. Based on mutagenicity and carcinogenicity scores, 1,3-dichloropropane would rank the highest and 2,2-dichloropropane the lowest. Application Of Future Chemical Sorting Procedures To The 1998 CCL Chemicals Procedures related to chemical properties, waste management, and resource productivity have been suggested for scoring and ranking chemicals in the future (Jensen et al., 1997). While only the procedures related to chemical properties were described in sufficient detail to warrant immediate consideration, there are merits to waste management and resource productivity approaches as evidenced by EPA's development of the Waste Minimization Prioritization Tool, which was proposed for public comment on June 23, 1997 (EPA, 1997b), substantially revised in response to public comments, and published with the Draft Resource Conservation Recovery Act Persistent Bioaccumulator Toxics list on November 9, 1998 (EPA, 1998b). Procedures related to chemical properties that might be considered in the future include flammability, ignitability, explosivity, oxidizability, reactivity, corrosivity, chemical-environmental interactions, global warming potential, ozone depletion potential, photochemical oxidant creation potential, odor threshold values, eutrophication potential, and acidification potential (Jensen et al., 1997). While criteria have been proposed to score all these chemical properties, it was not possible to use them to sort the 1998 CCL chemicals. However, two new procedures not considered by Jensen et al. (1997) could be used to sort the 1998 CCL chemicals. The first procedure, based on a chemical's mode of toxic action, was used in conjunction with SuCCSES classes to sort the 1998 CCL chemicals (See Table 4-10). Results from testing the acute toxicity of about 600 chemicals to fathead minnows were used to develop a computer-based expert system that predicts mode of toxic action based on chemical structure (Russom et al., 1997). The models and substructure search methods were designed for the ASsessment Tools for the Evaluation of Risk (ASTER) expert system and database. ASTER is an integration of the AQUatic toxicity Information REtrieval (AQUIRE)

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--> TABLE 4-9 Biological Effects Scores for Aliphatic Halides from the 1998 CCL Chemicals CAS No. Chemical Name Acute Toxicity Mutagenicity Carcinogenicity Ecotoxicity 000060-57-1 Dieldrin +3 +2 0 +3 000074-83-9 Methyl bromide +2 +2 0 +2 000075-34.3 1,1-Dichloroethane +1 +1 +1 +2 000079-34-5 1,1,2,2-Tetrachloroethane +2 +2 +2 +2 000087-68-3 Hexachlorobutadiene +2 +2 +1 +3 000142-28-9 1,3-Dichloropropane +1 +3 -2 +2 000309-00-2 Aldrin +3 +2 +2 +3 000542-75-6 1,3-Dichloropropene +2 +2 +3 +2 000563-58-6 1,1-Dichloropropene -1 +1 -1 -2 000594-20-7 2,2-Dichloropropane -1 -1 -1 -2

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--> TABLE 4-10 Modes of Toxic Action for the 1998 CCL Chemicals Arranged by SuCCSES Classes CAS No. Chemical Name Mode of Action   Acetanilides   034256-82-1 Acetochlor Nonpolar narcosis 051218-45-2 Metolachlor Nonpolar narcosis   Aliphatic halides   000060-57-1 Dieldrin Neurotoxicant: Cyclodiene-type 000074-83-9 Methyl bromide Nonpolar narcosis 000075-34-3 1,1-Dichloroethane Nonpolar narcosis 000079-34-5 1,1,2,2-Tetrachloroethane Nonpolar narcosis 000087-68-3 Hexachlorobutadiene Reactivity: Alkylation or arylation reaction 000142-28-9 1,3-Dichloropropane Nonpolar narcosis 000309-00-2 Aldrin Neurotoxicant: Cyclodiene-type 000542-75-6 1,3-Dichloropropene Reactivity: Alkylation or arylation reaction 000563-58-6 1,1-Dichloropropene Nonpolar narcosis 000594-20-7 2,2-Dichloropropane Nonpolar narcosis   Aromatic halides   000072-55-9 DDE Nonpolar narcosis 000108-86-1 Bromobenzene Nonpolar narcosis 000887-54-7 DCPA mono-acid degradate Nonpolar narcosis 002136-79-0 DCPA di-acid degradate Nonpolar narcosis   Aromatic hydrocarbons   000091-20-3 Naphthalene Nonpolar narcosis 000095-63-6 1,2,4-Trimethylbenzene Nonpolar narcosis 000099-87-6 p-Isopropyltoluene Nonpolar narcosis   (p-cymene)     Carbamic acid esters   000759-94-4 EPTC (s-ethyl-dipropylthio-carbamate) Nonpolar narcosis

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--> CAS No. Chemical Name Mode of Action   Elements   007429-90-5 Aluminum N.A.* 007439-96-5 Manganese N.A. 007440-23-5 Sodium N.A. 007440-42-8 Boron N.A. 007440-62-2 Vanadium N.A.   Ethers   001634-04-4 Methyl-t-butyl ether (MTBE) Nonpolar narcosis   Halophenols   000088-06-2 2,4,6-Trichlorophenol Polar narcosis 000120-83-2 2,4-Dichlorophenol Polar narcosis   Hydrazines   000122-66-7 1,2-Diphenylhydrazine Reactivity: hydrazines   Inorganics   014808-79-8 Sulfate N.A.   Nitroaromaties   000098-95-3 Nitrobenzene Nonpolar narcosis 000121-14-2 2,4-Dinitrotoluene Reactivity: dinitroaromatic group 000606-20-2 2,6-Dinitrotoluene Reactivity: dinitroaromatic group   Phenols   000051-28-5 2,4-Dinitrophenol Uncoupler of oxidative phosphorylation 000095-48-7 2-Methylphenol (o-cresol) Polar narcosis   Phosphonothioates   000944-22-9 Fonofos Organophosphate mediated acetylcholinesterase inhibition   Phosphorodithioates   000298-04-4 Disulfoton Organophosphate mediated acetylcholinesterase inhibition 013071-79-9 Terbufos Organophosphate mediated acetylcholinesterase inhibition

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--> CAS No. Chemical Name Mode of Action   Phosphorothioates   000333-41-5 Diazinon Organophosphate mediated acetylcholinesterase inhibition   Triazines   000121-82-4 RDX Nonpolar narcosis 001610-18-0 Prometon Nonpolar narcosis 002212-67-1 Molinate Nonpolar narcosis 005902-51-2 Terbacil Nonpolar narcosis 006190-65-4 Triazines (atrazine-desethyl) Nonpolar narcosis 021087-64-9 Metribuzin Nonpolar narcosis 021725-46-2 Triazines (cyanazine) Nonpolar narcosis   Ureas   000330-54-1 Diuron Nonpolar narcosis 000330-55-2 Linuron Nonpolar narcosis * N.A. = not available.

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--> TABLE 4-11 Carcinogenicity Concern Levels for the 1998 CCL Chemicals Arranged by SuCCSES Classes CAS No. Chemical Name Carcinogenicity Concern Levels Comments   Acetanilides     034256-82-1 Acetochlor Moderate +Data 05121845-2 Metolachlor Moderate     Aliphatic halides     000060-57-1 Dieldrin Moderate +Data 000074-83-9 Methyl bromide Moderate   000075-34-3 1,1-Dichloroethane Low - Data 000079-34-5 1,1,2,2-Tetrachloroethane Moderate + Data 000087-68-3 Hexachlorobutadiene Moderate + Data 000142-28-9 1,3-Dichloropropane Moderate   000309-002 Aldrin Moderate + Data 000542-75-6 1,3-Dichloropropene High + Data 000563-58-6 1,1-Dichloropropene Moderate   000594-20-7 2,2-Dichloropropane Low     Aromatic halides     000072-55-9 DDE Moderate + Data 000108-86-1 Bromobenzene Moderate   000887-54-7 DCPA mono-acid degradate Low   002136-79-0 DCPA di-acid degradate Low     Aromatic hydrocarbons     000091-20-3 Naphthalene Moderate + Data 000095-63-6 1,2,4-Trimethylbenzene Low   000099-87-6 p-Isopropyltoluene (p-cymene) Low     Carbamic acid esters     000759-94-4 EPTC (s-ethyl-dipropylthiocarbamate) Moderate     Elements     007429-90-5 Aluminum Low   007439-96-5 Manganese Low   007440-23-5 Sodium Low   007440-42-8 Boron Low   007440-62-2 Vanadium Low to moderate  

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--> CAS No. Chemical Name Carcinogenicity Concern Levels Comments   Ethers     001634-04-4 Methyl-t-butyl ether Moderate + Data   Halophenols     000088-06-2 2,4,6-Trichlorophenol Moderate + Data 000120-83-2 2,4-Dichlorophenol Low - Data   Hydrazines     000122-66-7 1,2-Diphenylhydrazine Moderate     Inorganics     014808-79-8 Sulfate Low     Nitroaromatics     000098-95-3 Nitrobenzene Moderate   000121-14-2 2,4-Dinitrotoluene High + Data 000606-20-2 2,6-Dinitrotoluene Moderate + Data   Phenols     000051-28-5 2,4-Dinitrophenol Moderate   000095-48-7 2-Methylphenol (o-cresol) Low     Phosphonothioates     000944-22-9 Fonofos Low     Phosphorodithioates     000298-04-4 Disulfoton Low - Data 013071-79-9 Terbufos Low - Data   Phosphorothioates     000333-41-5 Diazinon Low     Triazines     000121-82-4 RDX Moderate   001610-18-0 Prometon Low Equivocal data 002212-67-1 Molinate Moderate + Data 005902-51-2 Terbacil Low - Data 006190-65-4 Triazines (atrazine-desethyl) Moderate + Data for parent compound

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--> CAS No. Chemical Name Carcinogenicity Concern Levels Comments 021087-64-9 Metribuzin Low Equivocal data 02172546-2 Triazines (cyanazine) Moderate + Data for parent   Ureas     000330-54-1 Diuron Low - Data 000330-55-2 Linuron Moderate + Data

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--> TABLE 4-12 Wildlife Species Contaminated with the 1998 CCL Chemicals Chemical Species Records Individuals Matrix Range (µg/g) Aldrin Blue jay 1 1 Brain 0.04   Fulvous whistling duck 2 30 Liver 0.0021, 0.0094   Sharp-shinned hawk 1 1 Brain 0.04 Aluminum American alligator 3 13 Egg 1.3-2.0   American 2 12 Eggshell 52.36   crocodile     Egg 10.86   Black-crowned night-heron 1 7 Egg 9.55   Muskrat 3 76 Kidney 3.45-13.19   Peregrine falcon 10 10 Egg 6.74-17.4   Short-tailed shrew 5 5 Carcass 130.0-561.0   Snapping turtle 2 19 Liver 15.97, 78.83   White-footed mouse 4 4 Carcass 45.0-180.0 Boron Common tern 10 10 Egg 22.4-36.8   Peregrine falcon 3 3 Egg 0.75-1.29   Snapping turtle 1 12 Liver 3   Tree swallow 3 9 Egg 1.52-3.55 Diazinon American brant 2 21 Liver 0.003         Small intestine 0.002-3.2         Gizzard 0.12-0.77   American robin 2 3 Gizzard 1.5   Blackbird 1 60   blot given   Blue jay 2 3 Alimentary canal 0.09-3.48   Boat-tailed grackle 1 3 Gizzard 12   Bobwhite quail 1 160 Wing 2.93   Canada goose 12 112 Gizzard 0.34-9.13         Liver 0.014-0.05   Common grackle 4 72 Gizzard 16   Mallard 9 74 Brain 161         Gizzard 0.32-3000

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--> Chemical Species Records Individuals Matrix Range (µg/g) Disulfoton American robin 1 9   Not given; birds poisoned Naphthalene Common tern 6 6 Egg 0.01 for all Vanadium Common tern 7 7 Egg 0.005-0.007   Muskrat 3 76 Kidney 0.045-1.10   Short-tailed shrew 3 3 Carcass 0.5-0.7   Snapping turtle 1 12 Liver 0.85   White-footed mouse 1 1 Carcass 0.3 Manganese Birds: 20 species 94 1,006 Nine 0.005-20.2   Muskrat 3 76 Kidney 5.23-6.60   White-footed mouse 4 4 Carcass 8.6-16.00   American alligator 3 16 Egg 0.14-0.15   Pine snake 8 248 Carcass 11.72-16.27         Skin 1.35-7.26 DDE 102 bird species; 8 mammal species; 6 reptile species; 1 amphibian species 1,608 21,585   0.002-228.00 Dieldrin 77 bird species; 9 mammal species; I reptile species; I amphibian species 1,067 14,889   0.0007-21.60 NOTE: These data were extracted from the Contaminant Exposure and Effects—Terrestrial Vertebrates database (Rattner et al., 1999). The column labeled "records" refers to the number of records in the database for each species that contain the given contaminant. (A record can represent one or many individuals and usually gives a mean concentration of the chemical.) "Individuals" represents the total number of individuals for all records. "Matrix" is where the chemical concentration was measured, and "range" is the concentration range in the given matrix for each species (generally dry weight for metals and wet weight for organics).

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--> TABLE 4-13 Aliphatic Halides (not on the 1998 CCL) with Uses Similar to Those of 1,1,2,2-Tetrachloroethane (on the 1998 CCL)     Uses CAS No. Chemical Machinery Polystyrene SBR Rubber Rubber Varnish Total Uses 79-34-5 1,1,2,2- Tetrachloroethane X X X X X 5 71-55-6 1,1,1- Trichloroethane X X X X X 15 56-23-5 Carbon tetrachloride X     X X 9 79-00-5 1,1,2-Trichloroethane   X X   X 3 TABLE 4-14 Production, Use, and Environmental Release Volumes for Aliphatic Halides (not on the 1998 CCL) that Have Similar Uses to 1,1,2,2-Tetrachloroethane (on the 1998 CCL) Chemical Name Production Volume Use Volume Toxics Release Inventory Volume (lbs.) 1,1,2,2-Tetrachloroethane High Low 16,000 1,1,1-Trichloroethane Extremely high Medium to high 8,800,000 Carbon tetrachloride Extremely high Low to medium 400,000 1,1,2-Trichloroethane Very high Low 340,000

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--> TABLE 4-15 Log Octanol-Water Partition Coefficient (log Kow) Values, Soil, or Sediment Sorption Coefficient (Koc) Values, and Henry's Law Constants for Aliphatic Halides (not on the 1998 CCL) that Have Similar Uses to 1,1,2,2-Tetrachloroethane (on the 1998 CCL) Chemical Name Log Kow Koc Henry's Law Constant (atm m3/mol) 1,1,2,2-Tetrachloroethane 2.39 107 3.67E-04 1,1,1-Trichloroethane 2.49 85 1.72E-02 Carbon tetrachloride 2.83 71 2.76E-02 1,1,2-Trichloroethane 1.89 97 8.24E-04