Bioavailability and assimilation of sediment-associated benzo[a]pyrene by Ilyodrilus templetoni (oligochaeta)

Benzo[a]pyrene (BaP)-amended sediment was desorbed by a sequential batch method using an isopropanol solution wash. The observed isotherm showed no evidence of desorption resistance, as indicated by increased partitioning to the solid phase at low concentrations. This was consistent with the prediction of minimal desorption resistance for highly hydrophobic compounds using a biphasic model. Bioavailability of BaP in desorbed sediments was assessed by toxicokinetic measures of uptake, bioaccumulation, and elimination in the deposit-feeding, freshwater tubificid oligochaete Ilyodrilus templetoni. Worms were exposed to sediments with BaP concentrations of approximately 26 and 11 μg/g dry weight sediment after desorption for one and three batches, respectively. The I. templetoni tissue concentration attained an apparent steady state after approximately one month and resulted in a biota-sediment accumulation factor of approximately 1.3 for both sediments. This is consistent with the paradigm that pore-water concentration predicts the uptake of organic contaminants into lipids despite the literature data showing that the major uptake route for BaP is likely from the ingestion of sediment particles. Ilyodrilus templetoni exhibited a high assimilation efficiency (80%) during a single-gut passage, a low elimination rate (k_e = 0.0032 h ^-1), and negligible biotransformation of sediment-associated BaP.