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Equilibrium partitioning sediment benchmark
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<p>Equilibrium partitioning Sediment Benchmarks (ESBs) are a type of <a href="/facts/Aquatic_toxicology/4aRsBDS7">Sediment Quality Guideline (SQG)</a> derived by the <a href="/facts/United_States_Environmental_Protection_Agency/ghI985SI">US Environmental Protection Agency</a> (EPA) for the protection of <a href="/facts/Benthic/N3lM6P7I">benthic</a> organisms. ESBs are based on the <a href="/facts/Bioavailable/9l6na9MV">bioavailable</a> concentration of <a href="/facts/Contaminants/RC0L7KRy">contaminants</a> in <a href="/facts/Sediment/zsIH1A6U">sediments</a> rather than the dry-weight concentration. It has been demonstrated that sediment concentrations on a dry-weight basis often do not predict biological effects. 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 <a href="/facts/Toxic/qa96rs60">toxic</a> to benthic organisms. Other phases of the chemical are bound to sediment particles like <a href="/facts/Organic_carbon/noBXADsJ">organic carbon</a> (OC) or <a href="/facts/Acid_volatile_sulfides/mUVhzlHu">acid volatile sulfides</a> (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms. </p><p>Equilibrium partitioning (EqP) predicts the bioavailable concentration of a chemical under given sediment conditions by using partition coefficients. The bioavailable concentration in <a href="/facts/Interstitial_fluid/hzm4qatP">interstitial</a> 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. </p><p>The EPA Office of Research and Development (ORD) has published ESBs for approximately 65 pollutants or classes of pollutants including 34 <a href="/facts/Polycyclic_aromatic_hydrocarbon/K52xSfNC">PAHs</a>, metal mixtures (e.g., cadmium, chromium, copper, nickel, lead, silver, and zinc), and pesticides <a href="/facts/Dieldrin/eCohYQNo">dieldrin</a> and <a href="/facts/Endrin/yAWyr6IV">endrin</a> </p>