Sequestration and bioavailability of PAHS in sediments

The observation of desorption-resistance has led to suggestions that these contaminants may not be available to organisms and therefore may not need to be included when assessing potential contaminant uptake and risk to human and ecological health and the natural recovery of contaminated sediment systems. This hypothesis is tested by challenging the desorption-resistant fraction of a polynuclear aromatic hydrocarbon contaminated sediment with physico-chemical sorption and desorption studies and biological assays of availability as measured by accumulation in deposit feeding oligochaete worms. Results with several polynuclear aromatic hydrocarbons indicate that the pore-water paradigm is a solid basis for defining steady state uptake and bioavailability regardless of the route of contaminant uptake. The kinetics of uptake, however, were found to be related to the route of exposure and for benzo[a]pyrene, in which uptake is via sediment ingestion, found to be related to assimilation efficiency in the organism's gut. Gut juice extraction efficiency assays, which have been proposed as measures of bioavailability, would thus only be useful in assessing the kinetics of uptake of such compounds in the organisms studied. A dynamic model of pore water concentrations, which apparently controls steady state accumulation, is developed based upon partitioning from condensed and amorphous organic carbon phases in the sediment.