Effects of sediment‐bound polydimethylsiloxane on the bioavailability and distribution of benzo[a]pyrene in lake sediment to Lumbriculus variegatus

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Abstract
Oligochaetes, Lumbriculus variegatus, were exposed to Lake Michigan sediment spiked in the laboratory with polydimethylsiloxane (PDMS) at two different concentrations (50 and 150 μg g−1). Additionally, these sediment samples and one without PDMS were spiked with benzo[a]pyrene (BaP) (about 190 pg g−1). The accumulation of PDMS and BaP, survival, wet weight, and defecation of the animals were monitored. Lumbriculus variegatus accumulated sediment‐associated BaP rapidly and achieved steady state within 96 to 168 h. The BaP uptake clearances (ks, g sediment g−1 animal h−1) were 0.069, 0.060, and 0.056 for BaP only, BaP with low‐dose PDMS, and BaP with high‐dose PDMS exposures, respectively. The BaP bioaccumulation factor was reduced by PDMS in the sediment. Only very low concentrations of PDMS were found associated with the worms, which suggests some surface sorption or association with material in the gut. Elimination of BaP in clean sediment was rapid, but elimination in water was much slower. Elimination rate constants for BaP, ke, were 0.0229 ± 0.0011 h−1 for sediment and 0.0004 ± 0.0004 h−1 water‐only depuration. The PDMS was excreted within 10 h both in sediment and water‐only depuration exposures, indicating that most of the measured body burden was due to the sediment‐associated material inside the organisms' gut. Animals were not purged before analyses, and several approaches were investigated for estimating the contribution of the intestinal contents. Based on both measurements and calculations, sediment‐associated BaP in the gut contributes less than 10% of total body burden. Thus, a 10‐h water‐only purge was found to be the most appropriate method for eliminating the gut‐content influence on the body burden.

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