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PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISM: PAH MIXTURES
Citation:
PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISM: PAH MIXTURES. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-02/013 (NTIS PB2004-105774), 2002.
Description:
This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations of PAH 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 specific effect endpoint. In this document, the Final Chronic Value (FCV) for PAHs derived using the National Water Quality Criteria (WQC) Guidelines was used as the toxicity endpoint for this ESB. This value is intended to be the concentration of a chemical in water that is protective of the presence of aquatic life. For this PAH mixtures ESB, narcosis theory was used to (1) demonstrate that the slope of the acute toxicity-octanol water partition coefficient (KOW) relationship was similar across species; (2) normalize the acute toxicity of all PAHs in water to an aquatic species using a reference KOW of 1.0 (where the concentration in water and lipid of the organism would be essentially the same); (3) establish an acute sensitivity ranking for individual species at the KOW of 1.0 and to use the rankings to calculate a Final Acute Value (FAV) following the WQC Guidelines; (4) calculate the final acute-chronic ratio (ACR) from water-only acute and chronic toxicity tests; (5) calculate the Final Chronic Value (FCV) at the reference KOW of 1.0 from the quotient of the FAV and ACR; and (6) to calculate the PAH-specific FCV in mg/L using the FCV at the reference KOW of 1.0, the PAH-specific KOW, the slope of the KOW-KOC relationship and the universal narcotic slope of the KOW-acute toxicity relationship. The EqP approach and the slope of the KOW-KOC relationship was then used to calculate, from the product of the PAH-specific FCV and KOC, the FCV concentration for each specific PAH in sediment (COC,PAHi,FCVi, mg/g organic carbon). Based on this approach, the recommended ESB for total PAH should be the sum of the quotients of a minimum of each of the suggested 34 individual PAHs in a specific sediment divided by the COC,PAHi,FCVi of that particular PAH. This sum is termed the Equilibrium Partitioning Sediment Benchmark Toxic Unit (EESBTUFCV). Freshwater or saltwater sediments containing <1.0 EESBTUFCV of the mixture of the 34 PAHs or more PAHs are acceptable for the protection of benthic organisms, and if the EESBTUFCV is greater than 1.0, sensitive benthic organisms may be unacceptably affected.
The ESBs do not consider the antagonistic, additive or synergistic effects of other sediment contaminants in combination with PAH mixtures or the potential for bioaccumulation and trophic transfer of PAH mixtures to aquatic life, wildlife or humans.