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PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING SEDIMENT BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISMS: METALS MIXTURES (CADMIUM, COPPER, LEAD, NICKEL, SILVER, AND ZINC)
Hansen, D, D. M. DiToro, W J. Berry, W S. Boothman, R M. Burgess, G T. Ankley, D R. Mount, J. A. McGrath, L. D. DeRosa, H. E. Bell, M. C. Reiley, AND C S. Zarba. PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING SEDIMENT BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISMS: METALS MIXTURES (CADMIUM, COPPER, LEAD, NICKEL, SILVER, AND ZINC). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-02/011 (NTIS PB2006-102425), 2005.
This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations of metal mixtures in sediment which are protective of the presence of benthic organisms. The equilibrium partitioning (EqP) approach was chosen because it accounts for the varying biological availability of chemicals in different sediments and allows for the incorporation of the appropriate biological effects concentration. This provides for the derivation of benchmarks that are causally linked to the specific chemical, applicable across sediments, and appropriately protective of benthic organisms.
EqP can be used to calculate ESBs for any toxicity endpoint for which there are water-only toxicity data; it is not limited to any single effect endpoint. For the purposes of this document, the ESB for mixtures of the metals cadmium, copper, lead, nickel, silver, and zinc, the ESBAVS:WQC, is derived based on two complementary approaches. In the first approach, the ESBAVS:WQC is based on the solid phase and interstitial water phase of sediments. In sediments, these metals should not cause direct toxicity to benthic organisms if the ESEM-AVS is # 0.0. In the second approach, sediments containing these metals should not cause direct toxicity to benthic organisms if the sum of the dissolved interstitial water concentrations for each of the metals (EMi,d) divided by their respective Water Quality Criteria (WQC) Final Chronic Value (FCV) is #1.0. Uncertainty bounds on ESEM-AVS and (ESEM-AVS)/fOC can be used to identify sediments where toxicity, because of these metals, is unlikely, uncertain, or likely. If the ESEM-AVS is > 0.0 or EMi,d divided by their respective FCVs is >1.0, effects may occur with increasing severity as the degree of exceedance increases.
The ESBs do not consider the antagonistic, additive or synergistic effects of other sediment contaminants in combination with metal mixtures or the potential for bioaccumulation and trophic transfer of metal mixtures to aquatic life, wildlife or humans.