Toxic substances in surface water Protecting human health: m e Great Lakes experience
Was this j s h 's tumor caused by water-borne toxics ?
Jeffery A. Foran Division of Occupational and Environmental Medicine The George Washington University Washington, DC 20037 Traditionally, water quality programs for surface waters in the United States have been based on the protection of aquatic life, These regulatory programs have succeeded in mitigating many of the visible effects of pollutants and, in the process, have made waters more habitable for aquatic biota. Now, however, the scientific community is focusing its attention on the less visible, chronic impacts of toxic pollutants. For example, toxic substances accumulate in the tissues of aquatic organisms and pose health threats to humans and other 604
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organisms that consume contaminated biota. This problem has been particularly apparent in the Great Lakes basin (1, 2). The Clean Water Act (CWA) was designed to protect the nation's surface waters, their biota, and human health from impacts of conventional and toxic pollutants. For this purpose, water quality standards (WQS) , which define minimally acceptable quality of the nation's surface waters, were established under Section 303 of the Act. WQSs include narrative criteria for acceptable surface water quality, descriptions of designated uses for specific surface water systems, and language that addresses antidegradation (3). They also may consist of numeric criteria for toxic pollutants. EPA has developed numeric criteria
to protect aquatic life (4). These criteria generally serve as the basis for most state WQS programs, under which states have been granted authority for implementing CWA regulations for their waters. Far fewer in number, however, are criteria in state WQS programs for the protection of human health, based on acceptable concentrations of toxicants in fish flesh and in surface waters that serve as a drinking water source. For example, only two of the eight states in the Great Lakes basin included numeric human health criteria for toxic substances in their WQS programs before the CWA was amended in 1987. In other words, the regulation of the impacts of toxic substances on human health under the CWA has not progressed as rapidly as has regulation of toxic impacts on aquatic biota, even
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though human health risks posed by the consumption of aquatic organisms that are contaminated with toxic substances may be very high (5). Further, health risks associated with consumption of contaminated fish may be at least 20-40 times higher than health risks associated with exposure to the same chemicals through drinking water (6). Because of the paucity of numeric criteria to protect human health in state programs, Section 303(c)(2)(B) of the
1987 CWA amendments required, for the first time, the inclusion of numeric criteria for toxic substances in state WQS programs. Numeric criteria define specific concentrations of toxic substances in surface waters, above which these substances would pose undue risks to human health and to aquatic and terrestrial biota. They also serve as a regulatory tool for controlling the discharge of conventional and toxic pollutants from point sources through the National Pollutant Discharge Elimination System (NPDES) and from nonpoint sources. EPA offers states three options for adopting numeric criteria for toxic substances in their WQS programs (7) (see box). EPA suggests that option 2 most directly reflects the requirements of the CWA but that option 3, a procedural
approach to develop numeric criteria, may be used to supplement option 2 (7). The procedural approach involves developing state-specific formulae that allow the establishment of numeric criteria for toxic substances. The procedural approach does not rely on the direct adoption or use of existing EPA criteria in state WQS programs, but it may nevertheless result in state-specific criteria that are similar to criteria developed by EPA.
Although EPA has not encouraged the use of option 3 in state WQS programs, there are several advantages to adopting this approach: It allows development of criteria in the absence of criteria for 307(a) pollutants and for pollutants not listed in section 307(a) of the Act. It allows the consideration of site- or region-specific conditions. It allows the immediate use of the latest scientific information available when a state needs to develop a numeric criterion. It facilitates greater public scrutiny of the process used to develop numeric water quality criteria. To comply with the section 303(c)(2)(B) of the 1987 CWA amendments, most states have chosen options 1 or 2 rather than option 3 to include
human health and other numeric criteria in state WQS programs (D. Sabock, EPA, personal communication, October 1989). However, many states in the Great Lakes basin are either relying entirely on option 3 or are using combinations of options 2 and 3 to fulfill the requirements of the Act. The popularity of option 3 in the Great Lakes states results from the successful development and use of this approach in Michigan where, since 1985, procedures rather than specific numeric criteria have been used in the state WQS program. Because of the inherent advantages of using a procedural approach, states outside the Great Lakes region might consider the use of this approach as they revise their programs in the future (triennial review and revision is required by the CWA). In addition, without specific EPA guidance for the development of criteria to protect human health, many states may follow the lead of the Great Lakes basin states in development and use of option 3. This article discusses the procedures used by states in the Great Lakes basin to develop numeric criteria to protect human health from the impacts of carcinogens and noncarcinogens. Also presented are the risk management and exposure decisions made by the states during procedure development. Two examples of criteria derivation (for carbon tetrachloride and endrin) are shown to demonstrate how the choice of an acceptable cancer risk level and various exposure assumptions can influence criteria that are developed to protect human health from the impacts of toxic substances in surface waters.
Human carcinogen criterion The human carcinogen criterion (HCC) (Equation 1) is intended to protect humans from an unreasonable incremental risk of developing cancer resulting from contact with or ingestion of surface waters and from ingestion of aquatic organisms taken from surface waters. It is calculated as follows:
where HCC = human carcinogen criterion (mg/L); R41 = risk-associated intake (dose) in mg/kg-day (1/q? x cancer risk level); q? = EPA's cancer slope factor (the upper bound estimate of cancer potency from the linearized multistage model); Wh = weight of an average adult (70 kg); W, = adult water consumption (2 L/day); F = fish consumption rate (kg/day); BCF = bioconcentration factor for specific chemicals (L/kg) The HCC is determined for substances that are known, probable, or possible carcinogens by using standard Environ. Sci. Technol., Vol. 24, No. 5, 1990 605
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Adopt stat ride numer water quality criteria fc secti 307(a) toxic pollutants (priorit) illutants) for which EPA has aevelop criteria, regardless of whether me pollutants are known to be preseili the state’s waters; 2. Adopt specific numeric water quality criteria for section 307(a) toxic pollutants, for which EPA has developed criteria, as nec to support designated uses where pollutants are c h le re ’ 2xpected to ir rfe wil designated present in the waters and uses; aure TO caicuiare numeric water quality crireria for, 3. AaoD d~ a minimum; those section 307(a) toxic pollutants that are dischargnA or prpcnnt in thn watnrc a n d a r a nunm-t~rltn intarfar@with dwainnnt
risk assessment techniques as described in EPA’s “Guidelines for Quantitative Cancer Risk Assessment” (8). The HCC incorporates factors for exposure to toxic substances through the consumption of water and fish, and levels of chemical-specific bioconcentration or bioaccumulation (9). As a part of this procedure, the agency suggests that the criterion should address exposure via drinking water and consumption of fish, which necessitates the adoption of representative water and fish consumption rates. Further, the procedure must include consideration of incidental exposure from other water sources such as swimming; concurrent exposure to more than one toxicant through the concepts of synergism, additivity, or antagonism; and the contribution to total daily intake of toxicants from nonsurface water sources such as food, air, groundwater, and soil (7). States must choose a cancer risk level during development of a carcinogen criterion, because the agency does not propose adoption of a specific cancer risk level for HCC development. Instead, EPA water quality criteria documents (I 0) present ambient concentrations of a few individual toxicants associated with risk levels of and The agency suggests that a state should not be limited to choosing among the risk levels published in criteria documents.
Human noncarcinogen criterion The human noncarcinogen criterion (HNC), also known as the human threshold criterion (HTC), is intended to protect humans from adverse health effects that result from contact with noncarcinogenic substances through the ingestion of surface waters and of aquatic organisms from surface waters. Equation 2 is used to compute the HNC (in mg/L):
where R p = EPA reference dose (mg/ kg-day) (replaced by #I = allowable 606
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daily intake of a contaminant in mg/kgday, in most Great Lakes state programs); and EAF = exposure adjustment factor (dimensionless). No-observed-adverse-effect-level (NOAEL) , lowest-observed-adverseeffect-level (LOAEL), and LDS0 data may be used in place of R p or ADI if appropriate adjustment factors are applied (11, 12). The HNC or HTC is derived for toxic substances for which a clear threshold dose or concentration is known. Although this criterion is derived from EPA’s reference dose, most states in the Great Lakes basin still the use either the allowable daily intake, developed by the U.S. Food and Drug Administration, or the ADI established by the World Health Organization. The Rfo or ADI is derived by applying appropriate uncertainty or adjustment factors to NOAEL, LOAEL, or LD50 data. R p s are verified by an Intraagency Task Force and are listed in EPA’s Integrated Risk Information System (I I , 12). Like the HCC, the HTC incorporates exposure to toxic substances through water and fish consumption and chemical-specific bioconcentration or bioaccumulation factors. The determination of the HTC also may include consideration of incidental exposure from other water sources such as swimming, concurrent exposure to more than one toxicant (synergism, additivity, antagonism), and the contribution to total daily intake of toxicants from nonsurface water sources such as food, air, groundwater, and soil.
Criteria development All states in the Great Lakes basin (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin) have federally approved WQS programs and regulate the discharge of toxic pollutants from point sources via the NPDES. Six of the eight Great Lakes states (Table 1) have either adopted or proposed the adoption of a procedure to calculate human health criteria in their WQS programs. For
these procedures, states must choose values for an acceptable cancer risk level, representative fish and water consumption (drinking) rates, and average weights of individuals to be protected. States also must decide whether and how to address concurrent exposure to more than one toxicant, and whether and how to address exposure from multiple sources of the same toxicant. The risk levels and other assumptions used by the Great Lakes states in development of human health criteria are listed in Table 1. The Great Lakes states have chosen cancer risk levels of either or for the development of the human carcinogen criterion and fish consumption rates that range from 6.5 g/day to 33 g/day. These states, however, rely on different procedures to account for exposure from nonsurface water sources, and for concurrent exposure to combinations of toxicants. Minnesota and Wisconsin adjust the calculation of the noncarcinogen criterion to address exposure from sources other than surface water. This adjustment is made through the use of an exposure adjustment factor (Em.Wisconsin assumes that a fixed percentage (80%)of the total exposure (from all sources) to individual toxicants comes from consuming contaminated drinking water and contaminated aquatic biota. Thus the state multiplies the ADI by 0.8 to allow for up to 20% of total exposure from nonsurface water sources. Minnesota has developed an EAF based on the bioaccumulative properties of individual toxicants. For a substance that is highly bioaccumulative (as yet undefined, but generally substances with a 1og-Kw L 3) and therefore likely to occur at elevated concentrations in fish tissue, the state assumes that the majority (up to 80%) of total exposure will come from surface water sources. For a substance that does not tend to bioaccumulate, Minnesota assumes that no more than 20% of the substance comes from surface water related sources and multiplies the ADI by 0.2. Illinois, Minnesota, and Wisconsin address concurrent exposure to combinations of carcinogens in criteria development. These states develop the HCC by assuming that the risk of concurrent exposure to more than one carcinogen is expressed by the addition of risks associated with exposure to the individual contaminants in the mixture. Illinois, however, uses a less stringent total cancer risk level where exposure to more than one carcinogen is considered to calculate the HCC.
Exposure, risk levels, criteria The choice of a cancer risk level, the fish consumption rate, incorporation of
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exposures from nonsurface water sources, as well as consideration of concurrent exposure to more than one toxicant play important roles in the derivation of criteria. Two criteria derivations are presented below to demonstrate the influence of these factors: One for carbon tetrachloride (a carcinogen) and one for endrin (a noncarcinogen). Criteria are derived for these substances by using data (& BCI;I and ADZ) from Wisconsin's water quality standards Rule NR 105 (13) in Equations l and 2 and by incorporating the different cancer risk levels, fish consumption rates, and the E M S used by the Great Lakes states. The choice of E M , fish consumption rate, and cancer risk level for criterion development is critical for two reasons. First, the selection of exposure assumptions and a cancer risk level will determine maximum acceptable pollutant levels in surface waters. Less conservative exposure assumptions will result in higher allowable pollutant concentrations in ambient water. For the two contaminants presented here, use of the more conservative risk levels and exposure assumptions results in an HCC for
carbon tetrachloride that is 46 times lower, and an HTC for endrin that is 28 times lower than criteria derived for these compounds with use of least conservative risk and exposure assumptions (Table 2). Second, acceptable pollutant levels in surface water will determine the concentration and loads of pollutants that may be discharged from point sources that are regulated under the NPDES program. Less stringent allowable pollutant levels will result in development of less stringent effluent limits in NPDES permits where other variables (e.g., dilution and design flows) are held constant. This analysis considers criterion development for only single pollutants. Regulating exposure to more than one toxicant in criterion development is based on the assumption of additivity of risk or effect. For example, where an acceptable cancer risk level of has been adopted, the risk associated with concurrent exposure to more than one carcinogen is assumed to be additive and the total risk is not to exceed (or in Illinois). Thus the HCC for two carcinogens is derived by the expression:
CIICR1 + C2ICR2 1 1 (3) where C1and C2 are the concentrations of carcinogens 1 and 2, and CRI and CR2 are the criteria (maximum acceptable concentrations in surface water) for carcinogens 1 and 2 associated with individual risks of 1O-5. The use of this concept in criterion development reduces allowable concentrations of individual carcinogens in surface water well below levels allowed when criteria are based on risks or effects associated with exposure to individual toxicants only. Use of the additivity concept also results in more stringent effluent limits in NPDES permits where effluents contain more than one toxicant to be regulated under the state WQS program. Discussion The use of a procedural approach (option 3) to develop numeric criteria in state WQS programs provides flexibility in regulating toxic substances in surface water and protecting human health. The use of the procedural approach, however, has some important disadvantages. First, where several states, such as those surrounding Lake Michigan, share one surface water system, use of state-specific procedures to develop human health criteria may result in different criteria for the same toxic pollutant if states choose different risk levels or exposure assumptions. The adoption of different criteria for the same pollutant will result in different levels of regulation of the pollutant between states for the same water body. A state that has chosen less conservative exposure assumptions and derived a less stringent criterion for a toxic pollutant may require a less stringent degree of regulation for discharges of that pollutant. Different levels of protection of the shared resource then will occur, as will competition for industry and its associated economic advantages. The governors of the Great Lakes states signed an agreement in 1986 stating that the states would work cooperatively to develop uniform WQS programs. Moreover, these states agreed
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calculate numeric criteria to protect human not to compete for industry by providing economic advantages at the expense health. article was reviewed for suitability of environmental protection. The de- asThis an ES&T feature by Michael S. Connor, gree of cooperation between the Great Massachusetts Water Resources Authority, Lakes states in coordinating their WQS Boston, MA 02 129. programs since 1986 and the success of the governors’ agreement are not yet References clear. (1) Clark, J. R. et al. J . Great Lakes Res. Second, water quality criteria devel1984, IO, 38-47. oped by means of the procedures pre(2) Foran, J . A.; VanderPloeg, D. J . Great Lakes Res. 1989, 15, 476-86. sented in this paper, particularly criteria (3) Fed. Regist. 1983, 48(217), 51407. for carcinogenic substances, often are (4) Erickson, R. J.; Stephan, C. E.; “Calcuseveral orders of magnitude below the lation of the Final Acute Value for Water analytical capabilities available to deQuality Criteria for Aquatic Organisms”; U . S . Environmental Protection Agency. tect those substances in surface waters. NTIS/PB882 14994, National Technical For example, Wisconsin’s carcinogen Information Center: Springfield, VA, criterion for polychlorinated biphenyls 1988. ( 5 ) Foran, J. A.; Cox, M.; Croxton, D. Am. in Lake Michigan is 0.15 ng/L, generJ . Pub. Health 1989, 79, 322-25. ally 3-4 orders of magnitude below the (6) Connor, M. S . Environ. Sci. Echnol. concentration detectable by standard 1984, 8, 628-3 1. commercial methods available to state (7) “Guidance for State Implementation of Water Quality Standards for CWA Secagencies. States in the Great Lakes bation 303(c)(2)(B)”; Office of Water, Ofsin have dealt with this problem generfice of Water Regulations and Standards, ally by recognizing the analytical level Criteria and Standards Division, Environmental Protection Agency: of detection (LOD) as the point for reg. , - Washington, DC, 1989. ulatory action. Use of the LOD as the (8) Fed, Regist. 1986, 51, 33992-34003. point for regulatory action, however, (9) Veith. G. D.: Kosian. I? In Physical Bemay result in substantial contamination halior of PCBs in the G r m t Lakes; Mackay. D. et al., Eds.: Ann Arbor Sciof biota and potential health impacts on ence: Ann Arbor. MI, 1983. human consumers of these biota, be( I O ) Fed. Regist. 1980, 45, 793 18-59. cause the discharge of pollutants at con( 1 1 ) Barnes. D. G.: Dourson. M. Reg. ki d . Pharrnacol. 1988, 8 , 47 1-86. centrations below the LOD may never(12) Integrated Risk Information System theless exceed a water quality criterion. (IRIS); U . S . Environmental Protection In light of the substantial health risks Agency. Office o f Health and Environmental Assessment. ECAO. Cincinnati. posed by exposure to toxic substances OH, 1989. through surface water routes, the con( 13) Wis. Regist. 1989, 398, 5 1-52-29. sideration of human health protection in modifications to state WQS programs is an important component in meeting the requirements of section 303(c)(2)(B) of the CWA. The use of a procedural approach (option 3) to develop numeric criteria provides an effective method to regulate the impacts of toxic substances in surface waters. However, solutions to problems such as interstate differences in protecting shared resources and problems associated with analytical detection capabilities are required before the procedural approach can be implemented effectively throughout the nation. This article reflects the views of the author, and does not necessarily reflect the views of ACS, The George Washington University, or EPA.
Acknowledgments I thank the following individuals for their assistance in developing this paper: Ken Bartal, Dennis Clark, Michael Dobbs, Dan Dudley, Tim Eder, Barbara Glenn, James Grant, Rayne Lamey, David Maschwitz, Clark Olson, Jack Sullivan, Kathy Towler, Mark Van Putten, Laura Welch, David Zaber and John Zambrano. Portions of this paper were developed while the author was a scientist at the National Wildlife Federation’s Great Lakes office and a member of several state and federal advisory committees involved in developing procedures to
Jeflery A. Foran is an assistant professor of medicine and health care sciences in the Division of Occupational and Environmental Medicine, The George Washington University. He received his B. S. degree from the University of Michigan, his M.S. from Central Michigan University, and his Ph.D. from the University of Florida. He has served on the staff of the National Wildlife Federation and on the faculty in the Schools of Natural Resources and Public Health at the University of Michigan. Foran’s research concerns the interface between environmental toxicology and environmental policy.
