title: Nonequilibrium of organic compounds in sediment-water systems. Consequences for risk assessment and remediation measures.
abstract: In many cases, sediment risk assessment, and remediation rely on the assumption of equilibrium between chemical concentrations in sediment pore water and overlying surface water and thus rely on pore water concentrations only and do not additionally include assessment of the overlying water concentration. Traditionally, the validity of this assumption was insufficiently documented due to a lack of data. Recent studies using passive samplers, however, provided sufficient data for the first systematic evaluation of the extent of disequilibrium between sediment pore water and overlying surface water. Recent bioaccumulation studies reveal uncertainty as to which of these concentrations govern bioaccumulation by benthic organisms. Here, we provide the first review of studies measuring disequilibrium identifying general patterns and implications for the aforementioned areas of application. In most studies on water/sediment (dis)equilibrium, sediment pore water and overlying surface water are close to equilibrium. For lower molecular weight PAHs, overlying water concentrations tended to be relative low, which is tentatively ascribed to biodegradation in the water column. Substantial nonequilibrium was observed at some hot-spot locations such as in semistagnant harbors. In such cases, efficacy of sediment remediation measures to improve overlying water quality can be questioned because differences between overlying water concentrations at the hot-spots and those at reference locations typically are small. For nonequilibrium situations and some benthic taxa, exposure may be determined best by pore water concentrations. Improving our understanding in this area may further improve risk assessment of contaminated sediments.
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, PO Box 47, 6700 AA Wageningen, The Netherlands. paul.vannoort@wur.nl
authors.forename: P C M
authors.initials: PC
authors.lastname: van Noort
authors.forename: A A
authors.initials: AA
authors.lastname: Koelmans
mesh_terms: D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods; D052918:Environmental Restoration and Remediation; D019015:Geologic Sediments / Q000737:chemistry*; D009930:Organic Chemicals / Q000032:analysis*; D011078:Polychlorinated Biphenyls / Q000032:analysis; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis; D018570:Risk Assessment; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009930:Organic Chemicals; D011084:Polycyclic Aromatic Hydrocarbons; D014874:Water Pollutants, Chemical; D011078:Polychlorinated Biphenyls