United States Office of Water Environmental Protection Agency 4304 EPA-822-F-98-004 July 1998 FACT SHEET Draft Revisions to the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health Abstract The U.S. Environmental Protection Agency is proposing to revise the methodology used to develop human health water quality criteria published in accordance with the Clean Water Act. These revisions, once finalized, will replace the existing 1980 National guidelines and methodology. These revisions are being made at this time to incorporate the many significant scientific advances that have occurred during the past 18 years in such key areas as cancer and noncancer risk assessments, exposure assessments, and bioaccumulation in fish. Human Health Water Quality Criteria Human health water quality criteria are numeric values limiting chemical concentrations in ambient waters. The criteria are developed under Section 304(a) of the Clean Water Act of 1972 (CWA) and are based solely on data and scientific judgments on the relationship between pollutant concentrations and environmental and human health effects. Protective assumptions are made regarding the exposure intakes that humans may experience. These criteria do not reflect consideration of economic impacts or the technological feasibility of meeting the chemical concentrations in ambient water. The criteria are used by states and regions to establish water quality standards and ultimately provide a basis for controlling discharges or releases of pollutants. EPA Methodology for Deriving Criteria States and authorized Indian tribes must develop water quality standards that include designated uses and water quality criteria necessary to support those uses. The Methodology is the guidance for states and tribes to help them establish water quality criteria and standards to protect human health. It provides the detailed means for developing the water quality criteria, including systematic procedures for evaluating cancer risk, noncancer health effects, human exposure, and bioaccumulation potential in fish. EPA Methodology Revisions EPA periodically revises water quality criteria to ensure that they accurately reflect the latest scientific knowledge on the kind and extent of all identifiable effects on health and welfare which may be expected from the presence of pollutants in any body of water, including ground water. Since 1980, many significant scientific advances have occurred which necessitate the revisions. Specifically, advances in such key areas as cancer and noncancer risk assessments, exposure assessments, and bioaccumulation make the revisions critical at this time. Therefore, EPA is updating its Ambient Water Quality Criteria (AWQC) Methodology to provide states and tribes with the most current procedures to reflect these changes in risk and exposure assessment. States and tribes will need to modify their water quality criteria to be consistent with current Agency practices. General Background of the Revision Process To begin developing a "state-of-the-science" approach revising the 1980 AWQC National Guidelines, EPA (along with other federal agencies, state health organizations, Canadian health agencies, academies, environmental and industry groups, and consulting organizations) prepared an issues paper that described the 1980 methodology, discussed areas that needed strengthening, and recommended revisions. The paper was distributed for review and comment ------- and was examined at a 1992 workshop, where more than 100 participants discussed critical issues. Based on individual expertise, attendees were assigned to specific technical workgroups. The workgroups' topics included cancer risk, noncancer risk, exposure, microbiology, minimum data and bioaccumulation in fish. After reviewing the draft of the recommended revisions to the methodology developed by EPA and the workshop participants, a summary document was submitted for review and comment by the EPA Science Advisory Board (SAB). Once final comments and revisions had been received from the board, the recommendations were again reviewed at a meeting of the Federal State Toxicology and Risk Analysis Committee, where state representatives presented their opinions on the preliminary draft recommendations. Major Methodology Revisions The major revisions are in four assessment areas: noncancer, cancer, exposure, and bioaccumulation. Equations have been developed for deriving AWQC, including parameters relevant to these four assessment areas, which are derived from scientific analysis, science policy and risk management decisions. For noncarcinogens, the process for deriving an acceptable level of exposure—known as the Reference Dose (RfD) value—has evolved over time. • EPA has developed guidance on assessing noncarcinogenic effects of chemicals and for the RfD derivation. » The Methodology revisions recommend consideration of other issues related to the RfD process including: integrating reproductive/ developmental, immunotoxicity, and neurotoxiciry data into the calculation. • EPA intends to allow the use of a range around the RfD point estimate to reflect the inherent imprecision of the RfD. EPA would select the midpoint of the range as a default when calculating a 304(a) criteria value for use in state, tribal, or regional water quality standards and require justification if a state or tribe proposes a different value within the range. • EPA is recommending the use of quantitative dose-response modelling for the derivation of RfDs. For carcinogen (cancer) risk assessment, more sophisticated methods to comprehensively determine the likely mechanism that causes human carcinogenicity are being recommended. • EPA is recommending a mode of action (MoA) approach to determine the most appropriate low-dose extrapolation for carcinogenic agents. • The MoA approach follows EPA's 1996 proposal of revised cancer guidelines and considers all biological information (rather than just tumor findings). Changes in the area of exposure assessment include the following. • States and tribes are encouraged to use local studies on fish consumption that better reflect local intake patterns and choices. • EPA will recommend default fish consumption values for the general population, recreational fishers and subsistence fishers. • A factor to account for other sources of exposure, such as food and air is included when deriving AWQC for noncarcinogens and nonlinear carcinogens (i.e., the dose is not allocated to drinking water and fish consumption alone). The new National AWQC Guidelines place greater emphasis on the use of bioaccumulation factors (BAFs) compared to the 1980 Guidelines for estimating potential human exposure to contaminants via the consumption of contaminated fish and shellfish. • BAFs reflect the accumulation of chemicals by aquatic organisms from all surrounding media (water, food, sediment). Compared to Bioconcentration Factors (BCFs), which reflect chemical accumulation by aquatic organisms from water only, BAFs are considered to be better predictors of chemical accumulation by fish and shellfish for chemicals where exposure from food and ------- sediment is important (e.g., highly persistent, hydrophobia chemicals). • EPA gives preference to the use of high quality field data over laboratory or model- derived estimates for deriving BAFs, since field data best reflect factors which can affect the extent of bioaccumlation (e.g., chemical metabolism, food web structure). Methodology Revisions Implementation by EPA/States EPA's future role in developing AWQC for the protection of human health will include: • The refinement of the revised methodology based on public comments received, • The development of revised criteria for chemicals of high priority and national importance (including, but not limited to chemicals that bioaccumulate, such as PCBs, dioxin, and mercury), and • The development or revision of AWQC for some additional priority chemicals. EPA does not plan to completely revise all of the criteria developed in 1980 or those updated as part of the 1992 National Toxics Rule (NTR). Partial updates of all criteria may bejplausible. EPA encourages states, tribes and EPA Regional Offices to use the revised methodology to develop or revise AWQC to appropriately reflect local conditions. EPA believes that AWQC inherently require several risk management decisions that are, in many cases, better made at the state and regional level (e.g., fish consumption rates, target risk levels). EPA will continue to develop and update necessary toxicology and exposure data needed in the derivation of AWQC that may not be practical for the states and regions to obtain. Affect on State and EPA Regional Offices The revised methodology will provide more flexibility for decision-making at the state, tribal and EPA regional level. EPA believes the AWQC inherently require several risk management decisions that are, in many cases, better made at the state, tribal and regional level. It is most likely that the methodology will result in more stringent criteria for bioaccumulatives (due to the use of BAFs instead of BCFs) and generally similar, or less stringent, values of nonbioaccumulatives. Affect on Existing Criteria Existing criteria will continue to be used in the following ways: • As guidance to states, tribes and regions for use in establishing water quality standards; • As the basis for EPA promulgation of water quality standards; and • In establishing water quality-based permit limits for industrial effluent discharges (i.e., NPDES limits), where the criteria have been adopted by a state, tribe or region or promulgated by EPA. Until such time as EPA re-evaluates a chemical, subjects the criteria to appropriate peer review, and subsequently publishes a revised chemical- specific 304(a) criteria, the existing criteria remain in effect. Information For additional information concerning these recommended methodology revisions, contact Denis Borum, Health and Ecological Criteria Division (4304), 401 M Street, S.W., Washington, D.C., 20460 (telephone: 202- 260- 8996). You may view the Federal Register notice that describes these recommended methodology revisions on the Internet at: http://www.epa.gov/OST/. The notice gives complete information on how to obtain additional information, how to review the complete administrative record for these recommended methodology revisions, and how to solicit public comment. ------- |