Fate of sediment-associated pyrene and benzo

Bioaccumulation, depuration and biotransformation of radiolabelled pyrene and benzo[a]pyrene were studied in the freshwater oligochaete Lumbriculus variegatus in spiked Lake Mekrijärvi (Eastern Finland) sediment in two sets of experiments (I and II). In experiment I bioaccumulation, depuration and biotransformation of PAHs were studied. In experiment II biotransformation was investigated further using three different solvent extractions and the ability of L. variegatus to biotransform was based on the change of proportion of the parent PAH in tissue. Bioaccumulation of both chemicals was fast and an apparent steady level was reached within a week. Biotransformation results obtained by solvent extractions were in agreement with each other, although hexane appeared to be less efficient solvent for B[a]P than chloroform:methanol or ethyl acetate:acetone/cyclohexane. The relative proportion of parent PAHs in tissues decreased continously during the 504 and the 336 h exposures in experiments I and II, respectively. After 336 h exposure in experiment II, approximately 60% of pyrene and 90% of B[a]P associated radioactivity was still in the parent compound. Depuration of the parent compounds in clean sediment was fast. Most of the parent chemicals were depurated within 72 h but the possible biotransformation products remained mainly in tissues. Feeding behavior of the animals (sediment ingesting vs. noningesting) did not affect pyrene biotransformation but the proportion of parent B[a]P in tissues was larger in feeding animals. This was probably due to faster uptake rate of B[a]P to feeders than nonfeeders and slow biotransformation rate of the chemical. Our results suggest that biotransformation of pyrene and B[a]P in L. variegatus is likely and it should be taken into account when studying bioaccumulation of PAHs in assessing hazard of sediment contamination.