title: Modification of the equilibrium partitioning approach for volatile organic compounds in sediment.
abstract: Although weakly hydrophobic chemicals such as volatile organic compounds (VOCs) tend not to persist in sediments, they may nevertheless be present in some sediments because of recent or ongoing releases. Standard methods are not available for assessing risks to benthic invertebrates due to VOCs in sediment. More strongly hydrophobic organic chemicals are frequently assessed by using the equilibrium partitioning (EqP) approach, which predicts the bioavailable fraction of chemical (the concentration dissolved in pore water) from the sediment-sorbed fraction, assuming that partitioning is at equilibrium. As typically applied, the EqP approach is ineffective for assessing VOCs in sediment, because the standard EqP equation fails to account for the contribution of dissolved chemical to the total chemical concentration in sediment. For chemicals with low organic carbon-water partition coefficients (Kocs), this results in nonsensical sediment-quality benchmarks that are more conservative (i.e., lower) than benchmarks calculated by assuming 100% bioavailability. A modified EqP equation is presented that accounts for the dissolved fraction of total chemical concentrations in sediment. Results of the standard and modified EqP equations converge with increasing Koc and are essentially identical at log Koc values exceeding approximately 3.5.
authors.affiliation: ARCADIS, 26451 Curtiss Wright Parkway, Cleveland, Ohio 44143, USA. pfuchsman@arcadis-us.com
authors.forename: Phyllis C
authors.initials: PC
authors.lastname: Fuchsman
mesh_terms: D019985:Benchmarking; D001682:Biological Availability; D004785:Environmental Pollutants; D019015:Geologic Sediments / Q000737:chemistry*; D008962:Models, Theoretical; D009930:Organic Chemicals; D012995:Solubility; D014835:Volatilization; D014867:Water / Q000737:chemistry
chemical_list: D004785:Environmental Pollutants; D009930:Organic Chemicals; D014867:Water