Current method for setting dioxin limits in water requires reexamination By Judy LaKind and Erik RiJrcin
A primary goal of the Federal Clean Water Act is to prohibit the discharge of toxic pollutants in toxic amounts ( I ) . To meet this objective, federal and state regulatory agencies set standards for receiving water quality and limit pollutant concentrations in effluent discharges. EPA has been authorized to develop ambient water quality criteria to protect aquatic life and human health. Standards for protection of human health are generally more restrictive than those for aquatic life and therefore are used to establish effluent limits for pollutants of concern. Criteria established to protect human health are based on risk assessment formulations, which consider the potency of the contaminant and exposure pathways including drinking water and consumption of fish and shellfish. Water quality criteria apply to contaminants dissolved in the water column. However, many contaminants are hydrophobic, with low dissolved concentrations in water because of their tendency to sorb strongly to organic matter and their low solubilities. Therefore, the risk assessment formula used for developing criteria protective of human health is not appropriate for strongly hydrophobic chemicals because it does not address the substantial portion of these chemicals sorbed to organic matter. Because hydrophobic chemicals include some of the most potent compounds known to man and are environmentally pervasive, limiting their presence in the aquatic environment is of considerable import. Ambient water quality criteria The risk assessment formula currently used by EPA and state regulatory agencies that relates human health risks from consumption of contaminated fish and shellfish (drinking-water pathway is generally insignificant for hydrophobic substances and is omitted here) to a water quality criterion is:
C=
RL/q* X W FC X BCF
where C = ambient water quality criteri-
on (mg/L); R L = risk level; q* = cancer potency factor (mg/kg/day)-' (slope of the dose-response curve); W = the weight of a human; FC = fish consumption rate (g/day); and BCF= bioconcentration factor. Because problems associated with applying Equation 1 to strongly hydrophobic substances hinge on the use of a BCF, the definition of bioconcentration and its implications warrant discussion. Bioconcentration Bioconcentration is a measure of a contaminant's tendency to concentrate in tissues of aquatic organisms, where the uptake route of the chemical by the organism is through the gill membranes or other external body surfaces (2). The
0013-936X/90/0924-0963$02.50/0 0 1990 American Chemical Society
bioconcentration factor is the ratio of the contaminant concentration in an aquatic organism to the contaminant concentration in water (3). If contaminant uptake by fish or other aquatic organisms is due exclusively to direct uptake from water through the gill membranes, t h e tissue contaminant concentration can be determined by multiplying the contaminant concentration dissolved in water by the BCF. EPA has relied, in part, on theoretical BCFs (4) derived from correlations with octanol-water partition coefficients (Kow); these correlations are based on the assumption that mechanistically, the uptake of organic pollutants by organisms is analogous to partitioning between water and an organic phase (4). Environ. Sci. Technol., Vol. 24, No. 7, 1990 963
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Judy LaKind
Erik Rifkin Thus, the higher the KO, of a contaminant, the greater the amount of contaminant will end up in fish tissue as a result of bioconcentration. In an environment comprised of only aquatic organisms and water, this assumption is correct; however, significant fractions of hydrophobic substances sorb to organic matter in effluent, the water column, and sediment prior to coming in contact with aquatic organisms. Because the contaminant-rganic matter complex is too large to permeate the gill membrane (bioconcentrate) (5), the BCF applies only to substances dissolved in water. Therefore, although the BCF may increase with increasing KO,, the amount of the substance available for bioconcentrating is significantly r e duced. Because water quality criteria are related to fish contamination levels by use of a BCF (Equation l), application of water quality criteria is restricted to the levels of hydrophobic substances dissolved in the water column. We can look to 2,3,7,8-tetrachloro-dibenzo-pdioxin (dioxin) as an example of the problems associated with limiting only the dissolved fraction of hydrophobic substances.
Dioxin Dioxin is extremely hydrophobic [log KO, = 6.1 (6)]and strongly sorbs to or964
Environ. Sci. Technol., Vol. 24, No. 7, 1990
ganic matter (7,8). At equilibrium, several orders of magnitude more dioxin are sorbed to organic matter than are found dissolved in water. By using a BCF to establish ambient water quality criteria for dioxin, only dissolved dioxin in the aqueous environment is addressed. The remainder, sorbed to organic matter in the effluent, water column, or sediments, is not included in the risk assessment calculation. Therefore, the vast majority of dioxin molecules discharged into water bodies remains unaddressed. Two significant ramifications arise from this conclusion. First, EPA has not considered the primary route of dioxin exposure for aquatic organisms and, ultimately, humans. Although sorbed dioxin does not enter aquatic organisms’ tissue by way of the gills, it may be ingested. It has been demonstrated that bioconcentration of dioxin is insignificant compared to ingestion of contaminated matter (9, IO). Therefore, the use of a BCF does not accurately predict fish tissue contaminant levels for dioxin. Second, EPA has recommended a water quality criterion for dioxin of 0.013 parts per quadrillion (ppq) (ZI). States have proposed dioxin ambient water quality criteria ranging from 0.0018 ppq to 7.2 ppq. These proposed criteria appear to be extremely stringent, but in fact it is likely that actual concentrations of dissolved dioxin from most discharges are already lower than those criteria.
In summary, the use of a BCF in developing water quality criteria for dioxin and other strongly hydrophobic compounds does not address the route by which fish are becoming contaminated and effectively ignores more than 99% of these compounds that enter the aquatic environment.
Conclusions The Clean Water Act requires EPA to prohibit the discharge of toxic pollutants in toxic amounts. EPA, by convention, has fulfilled this mandate by regulating contaminant levels dissolved in the water with the use of a BCF. However, there appears to be only a narrow range of Kows for which the BCF approach is relevant: those compounds that have Kows low enough such that significant concentrations are present in the water column, but high enough such that their lipophilicity enables them to bioconcentrate in fish tissue (Table 1). If alternative methodologies for limiting discharges of hydrophobic substances are not considered, the objectives established by EPA and the states associated with exposure to dioxin and other hydrophobic substances, as well a s the mandate established by the Clean Water Act, may be compromised.
References (I)
Federal Water Pollution Control Act, 33 U.S.C. Section 1251 et seq. (“Clean Water Act”). (2) “Draft Technical Support Document for
Water Quality-Based Toxics Control”; U.S. Environmental Protection Agency. Office of Water: Washington, DC, Nov. 1989. (3 “EPA Guidance Manual: Bedded Sediment Bioaccumulation Tests”; U.S. Environmental Protection Agency. Environmental Research Laboratory: Newport, OR, Sept. 1989; EPA/600/x-89/302. “Ambient Water Quality Criteria for (4 2,3,7,8-Tetrachloro-benzo-p-dioxin”; U.S. Environmental Protection Agency: Washington, DC, 1984, EPA/440/5-84-007. Opperhuizen, A. et al. Chemosphere 1985,14, 1871-96. “Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish”; U.S. Environmental Protection Agency. Offices of Marine and Estuarine Protection and Water Regulations and Standards: Washington, DC, Sept. 1989, EPA/503/8-89-002. Lodge, K. B.; Cook, P. M. Chemosphere 1989,19,439-44. “Health Assessment Document for Polychlorinated Dibenm-p-Dioxins”;U.S. Environmental Protection Agency: Washington, DC, Sept. 1985, EPA/600/8-84/ 014F. (9) Batterman. A. R. et a]. Chemosphere 1989,19, 451-58. (10) Kuehl, D. W. et al. Chemosphere 1987, 17,667-79. (1 1) “Final Guidance Document on Section 304 (1) Listing and Permitting of Pulp and Paper Mills”; US. Environmental Protection Agency. Offices of Water Regulations and Standards and Water Enforcement and Permits: Washington, DC, March, 1989.
Judy LaKind, senior associate at Riflin and Associates, Inc., has a B.A. degree in geology f r o m The Johns Hopkim University, an M.S. degree in geology from the University of Wisconsin, Madison, and a Ph.D. in environmental engineering from The Johns Hopkim University.
Emerging Managing Resistance to Agrochemicals From Fundamental Research to Practical Strategies ain an understanding of the nature and ,mechanisms of pest resistance to insecticides, fungicides, and herbicides in this thought-provoking overview. Read about the latest progress and results from leading researchers, bringing together different scientific disciplines and various agronomic focuses. Find out how and why the findings reported in this 32-chapter book reinforce the idea that pest resistance to pesticides can be understood and combated effectively. Cover scientific topics such as: strategies to delay resistance structural and biochemical characterizationof resistance species 0 genetic modification of species to alter resistance characteristics e computer models for managing resistance 0
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Eric Riflin, president of Riflin and Associates, Inc., has a B.A. degree in biological sciences from Rutgers University, and an MS.degree and Ph.D. in zoology from the University of Hawaii. He also had a National Academy of Sciences Post doctoral Associateship at the Naval Medical Research Institute in Bethesda, MD.
Sure to provide valuable information for everyone working in the control of pests or involved in the production and use of agrochemicals. Maurice B. Green, Editor, Independent Consultant Homer M. LeBaron, Elitor, Ciba-Geigy Corporation William K. Moberg, Editor. E.I. du Pont de Nemours and Company Developed from a symposium sponsored by the Division of Agrochemicals of the American Chemical Society ACS Symposium Series No. 421 497 pages (1990) Clothbound ISBN 0-8412-1741-6 LC 89-77580
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Hazardous Waste Management ere is an insightful reference on developing technologies for treating and managing wastewater and solid residuals that are contaminated with hazardous chemicals. Written by leading authorities in the field, this volume’s 22-chapters cover such diverse topics as municipal solid wastes, water purification by radiation (solar and UV), the isolation of organic species and inorganic radionuclides, and solvent recycling. Several chapters cover radiolysis chemistry in dilute aqueous media, solar treatment, chemical separations, the biological and chemical treatment of soils and sludges, and solids immobilization. This concise presentation draws from a variety of science and engineering disciplines with specific emphasis on physical, inorganic/ organic, and biological chemistry. It provides an across-the-board perspective of problems and proposed management technologies. This volume will serve as a useful introduction to hazardous waste treatment for the novice as well as a valuable reference for the technical expert. D. William Tedder, Editor, Georgia Institute of Technology Frederick G. Pohland, Editor, University of Pittsburgh
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Developed from a symposium sponsored by the Division of Industrial and Engineering Chemistry, Inc., of the American Chemical Society ACS Symposium Series No. 422 41 6 pages (1 990) Clothbound ISBN 0-8412-1747-5 LC 90-20 $89.95 American Chemical Society
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