For nonpolar organic compounds, such as organochlorines and polycyclic aromatic hydrocarbons (PAHs), SQCs have been derived based on thresholds for toxicity of compounds in water and the relative hydrophobicity of individual compounds. Water quality criteria, based on results of laboratory toxicity tests, are assumed to represent toxicity thresholds in porewater. Although direct measurement of concentrations of nonpolar organics in porewater is often difficult, porewater concentrations can be modeled by assuming that these compounds partition between sediment organic carbon (SOC) and porewater. The SOC:water partitioning behavior of individual compounds is assumed to be represented by octanol:water partitioning coefficients (DiToro et al. 1991).
Efforts to derive criteria for cationic metals have taken a different approach, largely because no single sediment component controls metal bioavailability across a variety of sediment environments. The most widely-used approach to model metal bioavailability in sediments is based on the tendency of many toxic metals (Cd, Cu, Pb, Ni, and Zn) to form highly-insoluble metal sulfides in the presence of acid-volatile sulfide (AVS). Metals are predicted to be unavailable (and sediments non-toxic) if the molar sum of the concentrations of metals is less than the molar concentration of AVS (Ankley et al. 1996). This model defines a conservative "no-effect" condition, rather than a true SQC. The model does not consider the sorption of metals to sediment components other than AVS, notably organic carbon and hydrous metal oxides. An alternative approach, based on direct measurement of metals in porewater, is limited by difficulties of defining and analyzing bioavailable forms of aqueous metals.
The importance of bioaccumulation processes in mediating contaminant availability in aquatic ecosystems has resulted in the recent development of standard bioassay procedures for measuring bioaccumulation from sediments. Standard bioassays fir assessing bioaccumulation from freshwater sediments use the oligochaete worm, Lumbriculus variegatus (methods have also been developed for marine molluscs and polychaete worms; USEPA 1994, ASTM 1996). Oligochaetes have several advantages for bioaccumulation assays, including: burrowing habits, relative insensitivity to toxicity, and limited ability to metabolize contaminants. The standard methods specify exposure duration, stocking densities, water-replacement rates, and gut-clearance procedures.
Bioaccumulation assays have been characterized to assure that the method is appropriate for studying a wide range of nonpolar organic compounds, and that the results obtained reflect bioavailability under field conditions. Studies of bioaccumulation kinetics of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides were used to select an optimal (28 day) exposure duration (Brunson et al. 1993). Field-validation studies with sediments from the Upper Mississippi River indicated that the bioaccumulation assay accurately identified the suite of compounds accumulated by native oligochaetes, and that concentrations of individual compounds were generally similar between field-collected and lab-exposed oligochaetes. Observed differences between bioaccumulation in the lab exposed and field-collected oligochaetes were related to molecular weight/hydrophobicity of compounds and associated differences in bioaccumulation kinetics (Brunson et al. 1996).
Studies of metal bioaccumulation from sediments have also proved to be useful tools for assessing ecological risks from metal-contaminated sediment and for investigating influences on bioavailability and mobility of metals in sediments. For example, diets containing metal-contaminated invertebrates from the upper Clark Fork River in Montana have been found to reduce survival and growth of juvenile trout (Woodward et al. 1994). Laboratory bioaccumulation studies with Clark Fork sediments found that uptake of Cu and Zn from sediment by the amphipod, Hyalella azteca, corresponded closely to metal concentrations in field-collected invertebrates (Ingersoll et al. 1994). Bioaccumulation tests with larvae of the midge, Chironomus tentans, found that bioavailability of Cu was negatively associated with concentrations of AVS and organic carbon in sediments (Besser et al. 1995), and that changes in AVS concentrations were an important factor affecting spatial and temporal variation in metal bioavailability in Clark Fork sediments (Besser et al. 1996).
Methods under consideration for selective reduction of the bioavailability of nonpolar organics and cationic metals are based on the same principles used for development of sediment quality criteria. Preliminary studies have used the addition of a non-polar resin (Ambersorb) to reduce the toxicity of nonpolar organic compounds, and addition of excess AVS or complexing agents (e.g. EDTA) to reduce bioavailability of cationic metals. The effectiveness of these treatments has been inconsistent in preliminary results (Mount et al. 1996; D. Mount, USEPA, Duluth, MN, personal communication).
Efforts to selectively reduce the toxicity of ammonia in sediments have focused on sorption of the ammonium ion using a natural zeolite mineral, clinoptilolite. Addition of clinoptilolite to whole sediment substantially reduces porewater ammonia concentrations and reduces or eliminates toxicity to amphipods and midges (Besser et al. 1996). Additional studies suggest that zeolite additions do not reduce the toxicity of cationic metals (Cd and Cu) in similar short-term bioassays.
Ankley, G.T. and Schubauer-Berigan, M.K. 1995. Background and overview of current sediment toxicity identification procedures. J. Aquat. Ecosystem Health. 4:133-149.
Ankley, G.T., Di Toro, D.M., Hansen, D.J., and Berry, W.J. 1996. Technical basis and proposal for deriving sediment quality criteria for metals. Environ. Toxicol. Chem. 15:2056-2066.
Besser, J.M., Kubitz, J.A., Ingersoll, C.G., Braselton, E., and Giesy, J.P. 1995. Influences on copper bioaccumulation and growth of the midge, Chironomus tentans, in metal contaminated sediments. J. Aquat. Ecosystem Health 4:157-168.
Besser, J.M., Ingersoll, C.G., and Giesy, J.P. 1996 Effects of spatial and temporal variability of acid-volatile sulfide on the bioavailability of copper and zinc in freshwater sediments. Environ. Toxicol. Chem. 15:286 293.
Brunson, E.L., et al. 1993. Bioaccumulation kinetics and field-validation of whole sediment exposures with the oligochaete, Lumbriculus variegatus. Abstracts, 14th annual meeting of SETAC (Houston, Texas). Society of Environmental Toxicology and Chemistry, Pensacola FL.
Brunson, E.L., T.J. Canfield, F.J. Dwyer, C.G. Ingersoll, and N.E. Kemble. 1996b An evaluation of bioaccumulation with sediments from the Upper Mississippi River using field-collected oligochaetes and laboratory exposed Lumbriculus variegatus. Chapter 2 in: Brunson, E.L. et al. An Assessment of Sediments from the Upper Mississippi River, Draft Report, USEPA Office of Science and Technology, Washington D.C.
DiToro, D.M., Zarba, C.S., Hansen, D.J., Berry, W.J., Swartz, R.C., Cowan, C.E., Pavlou, S. P., Allen, H.E., Thomas, N.A., and Paquin, P.R. 1991 Technical basis for establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning. Environ. Toxicol. Chem. 10:1541 1583.
Ingersoll, C.G. Brumbaugh, W.G. Dwyer, F.J., and Kemble, N.E. 1994 Bioaccumulation of metals from sediments by benthic invertebrates. Environ. Toxicol. Chem. 13:2013-2020.
Ingersoll, C.G., G.T. Ankley, D.A. Benoit, G.A. Burton, F.J. Dwyer, I.E. Greer, T.J. Norberg-King, and P.V. Winger. 1995. Toxicity and bioaccumulation of sediment-associated contaminants with freshwater invertebrates: A review of methods and applications. Environ. Toxicol. Chem. 14:1885-1894.
Ingersoll, C.G, J.M. Besser, and F.J. Dwyer. 1997. Development and application of methods for assessing the bioavailability of contaminants associated with sediments: I. Toxicity and the sediment quality triad. (this volume).
Mount, D.R. Ankley, G.T. West, C.W. Kosian, P.A. and Makeynen, E.A. 1996. Use of non-polar resin for in situ control of organic contaminant bioavailability in sediments. Abstracts, 17th Annual Meeting of SETAC (Washington, D.C.). Society of Environmental Toxicology and Chemistry, Pensacola, FL.
United States Environmental Protection Agency (USEPA). 1994. Methods for measuring the toxicity and bioaccumulation of sediment-associated contaminants with freshwater invertebrates. EPA 600/R-94/024, Duluth, MN.
Woodward, D.L., Brumbaugh, W.G., DeLonay, A.J., Little, E.E, and Smith, C.E. 1994. Effects on rainbow trout fry of a metals-contaminated diet of benthic invertebrates from the Clark Fork River, Montana. Trans. Amer. Fish. Soc. 123: 51-62.
Autobiography:John M. Besser, Research Fisheries Biologist, Midwest Science Center, USGS-Biological Resources Division, 4200 New Haven Road, Columbia, MO 65201. Education and Experience: Ph.D., Environmental Toxicology (Michigan State Univ.); M.S. Fisheries and Wildlife (Univ. of Missouri); B.S., Environmental Science/Biology (Univ. Wisconsin-Green Bay). Seventeen years of research experience with U.S. Fish and Wildlife Service, National Biological Service, and USGS. Research Interests: bioavailability and toxicology of trace elements; impacts of contaminated sediments on benthic invertebrates. Current research: (1) development of laboratory methods for assessment of toxicity and bioaccumulation from contaminated freshwater sediments; and (2) assessment of impacts of metals on biota of the upper Animas River, Colorado, as part of the USGS Abandoned Minelands Initiative.
Contributions from Other Federal Agencies
Contribution from the USGS