Relative Importance of Ingested Sediment Versus Pore Water as Uptake Routes for PAHs to the Deposit-Feeding Oligochaete Ilyodrilus templetoni

Abstract

The relative role of sediment pore water and ingested sediment particles to the total uptake of sediment-associated hydrophobic organic contaminants was examined by estimation from a water-only exposure experiment and from a bioenergetic-based toxicokinetic model utilizing experimentally measured sediment ingestion rates, assimilation efficiencies, and elimination rates. Phenanthrene (PHE) and benzo[a]pyrene (BaP) uptake in the bulk deposit-feeding oligochaete, Ilyodrilus templetoni, was measured. Assimilation efficiencies (ASE) were measured using a pulse-chase technique, based on a single-gut-passage time. Sediment-associated phenanthrene exhibited a lower ASE (50%) compared to BaP (80%), possibly due to a general relationship between assimilation and compound logK _ow. Estimated uptake of phenanthrene from pore water alone was essentially equal to the observed total uptake from both ingested sediment and sediment pore water. Estimated contribution of sediment-bound phenanthrene accounted for less than 20% of the total uptake. For benzo[a]pyrene, estimated uptake from sediment ingestion accounted for essentially all of the total uptake and estimated absorption from pore water accounted for <5% of the total uptake. This research provides direct experimental evidence for a predicted increase in the importance of sediment ingestion relative to the pore water route of exposure as the hydrophobicity of organic contaminants increases.