Setting Priorities for Drinking Water Contaminants (1999) / Chapter Skim
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2 Review of Existing Chemical Prioritization Schemes
2 Review of Existing Chemical Prioritization Schemes
Pages 21-46
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From page 21... ...
The remaining four (the Hazard Ranking System; Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) priority listing; Hazard Analysis of Releases Inventory, and the Pesticide Leaching Potential Index)
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From page 22... ...
Hazard Ranking System Comprehensive Environmental Response, Compensation, and Liability Act Priority List of Hazardous Substances Interagency Testing Committee (Walker and Brink, 1989; Walker, 1991; Walker, 1995) California Environmental Protection Agency (OEHHA, 1997)
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From page 23... ...
"Prioritization scheme" refers to the means by which exposure and toxicity are combined to provide a metric for ranking or prioritizing the contaminant. REVIEW OF CHEMICAL PRIORITIZATION SCHEMES Cadmus Risk Index Approach The Cadmus approach is a health-risk-based methodology for ranking a candidate list of drinking water contaminants.
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From page 24... ...
The quantity released to ambient water is the sum of the quantity released to surface water as determined from the Toxics Release Inventory (TRI) database, the quantity released to surface water as determined from the Permit Compliance System chemical release database, and the quantity released to ground water as determined from the TRI database.
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Assignment of the weights used in the averaging relationships that ultimately determine the HR score was inadequately explained in the report and is another example of the subjective nature of the determination of the various components of the risk index. Prioritization Scheme The overall risk index (RI)
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This process is described in a report entitled A Screening Process for Identifying Contaminants for Potential Drinking Water Priority Listing and Regulation (RCG et al., 1993~. Selection of Contaminant Pool The AWWA screening process was not applied to any specific list of chemicals.
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Prioritization Scheme As described above, the AWWA screening approach first screens chemicals based on toxicity criteria. Once a chemical has been judged to have significant health effects, the screening process evaluates the potential for exposure.
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While the RDP does not spell out what criteria should be used to select chemicals for occurrence monitoring, the process does emphasize that EPA should give significant weight to occurrence data. Thus, according to the RDP, the agency should establish a robust unregulated contaminant occurrence monitoring program that can be used to select contaminants for the Drinking Water Contaminant Candidate List (CCL)
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From page 29... ...
An advantage of this approach, unlike the AWWA screening process, is that it does not eliminate contaminants from consideration based on technological or economic feasibility of treating the contaminant; instead it leaves such decisions to risk managers. A drawback to this approach, however, is that the absence of health effects data on a contaminant may significantly curtail the development of a frequency distribution of risk and would preclude inclusion of the chemical on the CCL even though there are occurrence monitoring data.
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From page 30... ...
Prioritization Scheme The WMPT assigns a score to each of the three exposure factors (bioaccumulation potential, persistence, and mass) and the toxicity factor.
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It is important to emphasize that the additive relationship results simply from a mathematical transformation of a multiplicative relationship of the factor values. Interagency Testing Committee Approach The Interagency Testing Committee (ITC)
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Determination of Exposure Prior to 1986, a panel of experts assigned consensus scores to 11 exposure factors, including annual production, fraction released in the plant, number of workers potentially exposed, fraction released to the environment, number of people exposed in the general population, frequency of general population exposure, intensity of general population exposure, persistence, penetrability, influence on the environment, and bioaccumulation potential. Scores ranged from 0 to 3.
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From page 33... ...
Chemicals from sources of environmental monitoring data and substructures with potential to cause adverse health or ecological effects are assigned codes, and these values are used to select chemicals with environmental exposure and adverse effect potential. (Chemicals with no or low effects potential or low or no exposure potential are removed from the list and recycled.)
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From page 34... ...
Determination of Exposure OEHHA does not use exposure information in the assignment of hazard priorities, but it accounts for this information in the selection of chemicals from the "Candidate List" for committee consideration, as discussed below. The tracking database records chemical use and occurrence information, such as whether the chemical is used in California industries, is a byproduct of industries operating in California, is a pesticide used on food crops grown or imported into California, or is a component of consumer products or drugs sold in California.
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Selection of Contaminant Pool (contaminants considered in the HRS are determined by the hazardous substances, as defined in CERCLA regulations, found at the site. Determination of Exposure For a given site, the HRS evaluates exposure in ground water (gw)
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Prioritization Scheme The hazard score for each of the four pathways is computed from a multiplicative relationship of three factors: LR, WC, and T For example, for the ground water pathway, the hazard score is computed as: (LR)
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Selection of Contaminant Pool All contaminants present at NPL sites are considered for the CERCLA priority list of hazardous substances. Currently, the HAZDAT database lists more than 2,800 substances occurring at NPL sites.
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. Determination of Toxicity The CERCLA hazardous substance prioritization scheme considers toxicity by using the RQ approach, which was developed by EPA for guidance regarding environmental releases of hazardous substances.
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chemical release data and prioritization of watersheds for collecting additional information to establish a baseline for future inventories. The HAZREL score is an index of the magnitude of potential sediment contamination based on specific releases, physical and chemical properties, and potential environmental risk.
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However, the HAZREL score relies primarily on a determination of aquatic toxicity, which is not applicable for setting drinking water standards, and certainly the sediment aspects of the HAZREL score are not directly applicable to drinking water. Pesticide Leaching Potential The Groundwater Technology Section of the Environmental Fate and Groundwater Branch of EPA developed a numerical scale called the Pesticide Leaching Index, or Groundwater Leaching Index, to determine the annual risk or hazard from pesticide use with respect to ground water contamination (Wolf, 1996~.
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Therefore, the index is only an estimate of potential exposure. Prioritization Scheme The Pesticide Leaching Index is a function of an attenuation factor.
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Prioritization schemes that characterize exposure in an observational fashion include the CERCLA prioritization scheme, the AWWA screening process, and the proposed Regulation Development Process. These methods use monitoring data for the concentrations of contaminants in the environment to indicate exposure potential.
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Schemes designed to serve as quantitative risk-ranking schemes rely on complete, high quality data for both exposure potential and toxicity. Of the ten schemes examined, those that fall into this category include the WMPT, the HRS, the CERCLA priority listing, the Cadmus approach, HAZREL, the Pesticide Leaching Potential, and Section 4(e)
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1996. 1995 CERCLA Priority List of Hazardous Substances That Will Be the Subject of Toxicological Profiles & Support Documents.
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1995. Estimation methods used by the TSCA interagency testing committee to prioritize chemicals for testing: exposure and biological effects scoring and structure activity relationships.
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