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Equilibrium partitioning Sediment Benchmarks (ESBs) are a type of Sediment Quality Guideline (SQG) derived by the USEPA for the protection of benthic organisms. ESBs are based on the bioavailable concentration of contaminants in sediments rather than the dry-weight concentration. It has been demonstrated that sediment concentrations on a dry-weight basis often do not predict biological effects.〔United States Environmental Protection Agency. 2003. Technical basis for the derivation of equilibrium partitioning sediment benchmarks (ESBs) for the protection of benthic organisms: Nonionic organics. EPA-600-R-02-014. Office of Research and Development. Washington, DC. (draft)〕 Interstitial water concentrations, however, predict biological effects much better. This is true because the chemical present in the interstitial water (or pore water) is the uncomplexed/free phase of the chemical that is bioavailable and toxic to benthic organisms. Other phases of the chemical are bound to sediment particles like organic carbon (OC) or acid volatile sulfides (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms. Equilibrium partitioning (EqP) predicts the bioavailable concentration of a chemical under given sediment conditions by using partition coefficients. The bioavailable concentration in interstitial water can then be compared to an established water-based effect concentration and used to predict the likelihood of adverse effects. When a chemical exceeds the ESB, an adverse biological effect may occur, and when concentrations are below or equal to an ESB, biological effects are unlikely to occur. The USEPA's Office of Research and Development (ORD) has published ESBs for approximately 65 pollutants or classes of pollutants including 34 PAHs,〔U.S. Environmental Protection Agency. 2003. Procedures for the derivation of equilibrium partitioning sediment benchmarks (ESBs) for the protection of benthic organisms: PAH mixtures. EPA 600/R-02/013. Technical Report, Washington, DC.〕 metal mixtures (e.g., cadmium, chromium, copper, nickel, lead, silver, and zinc),〔U.S. Environmental Protection Agency. 2005. Procedures for the derivation of equilibrium partitioning sediment benchmarks (ESBs) for the protection of benthic organisms:Metal mixtures. EPA 600/R-02/011. Technical Report, Washington, DC.〕 and pesticides dieldrin〔U.S. Environmental Protection Agency. 2003. Procedures for the derivation of equilibrium partitioning sediment benchmarks (ESBs) for the protection of benthic organisms: Dieldrin. EPA 600/R-02/010. Technical Report, Washington, DC.〕 and endrin〔U.S. Environmental Protection Agency. 2003. Procedures for the derivation of equilibrium partitioning sediment benchmarks (ESBs) for the protection of benthic organisms: Endrin. EPA 600-R-02-009. Technical Report. Office of Research and Development, Washington, DC.〕 == Theory == Equilibrium partitioning theory (EqP) forms the basis for ESBs developed to account for bioavailability of contaminants in sediments. The concentration of interstitial water reflects the chemical's activity and is a surrogate for bioavailability.〔Di Toro DM, Zarba CS, Hansen DJ, Berry WJ, Swartz RC, Cowan CE, Pavlou SP, Allen HE, Thomas NA, Paquin PR. 1991. Technical basis for the equilibrium partitioning method for establishing sediment quality criteria. Environ Toxicol Chem 11:1541–1583.〕 EqP theory holds that a non-ionic chemical in sediment partitions between sediment OC, interstitial water and benthic organisms. For cationic metals, the chemical also partitions onto sediment AVS, as well as sedimentary OC. At equilibrium, if the partition coefficients are known along with the concentration in any one of the phases, then the concentrations of the other phases can be predicted. Using EqP theory, the bioavailable concentration of chemicals is predicted and then related to an established toxic effect concentration such as the final chronic value (FCV), which is used to derive water quality criteria (WQC) in the US.〔Stephan CE, Mount DI, Hansen DJ, Gentile GH, Chapman GA, Brungs WA. 1985. Guidelines for deriving numerical national water quality criteria for the protection of aquatic organisms and their uses. PB85– 227049. Technical Report. National Technical Information Service, Springfield, VA, USA.〕 Other values besides the FCV may also be used when an FCV is not available. Using water-based effects concentration when predicting toxic effects in benthos has been supported by studies showing similar effects occur in pelagic and benthic organisms.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Equilibrium partitioning sediment benchmarks」の詳細全文を読む スポンサード リンク
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