| This research characterizes the ability of activated carbon to reduce the bioavailability of polychlorinated biphenyls (PCBs) from field-contaminated sediment to clams, and employs a biodynamic model to describe PCB bio-uptake. PCBs remain a top contaminant of concern for today's scientists and engineers because they are ubiquitous, recalcitrant, and bioaccumulative. Activated carbon amendment has recently emerged as a promising new technology for the sequestration of PCBs in low-level contaminated sediment. This work provides a scientific basis for activated carbon amendment by demonstrating that the bioavailability of radiolabeled 2,2',5,5'-polychlorinated biphenyl (PCB-52) and benzo[a]pyrene (BaP) to the clam Macoma balthica is greatly diminished when sorbed to activated carbon versus other particle types including diatoms, wood, char, coke, peat, and coal. Specifically, if a clam ingests an activated carbon particle spiked with PCB-52, less than 2% of the contaminant is assimilated by the clam (absorption efficiency = 1.44 +/- 0.75%) versus almost 90% when the chemical is bound to diatoms. Twenty-eight day bioaccumulation tests using Macoma balthica and sediment from Hunters Point Naval Shipyard (San Francisco, CA) show that activated carbon amendment can reduce clam uptake of PCBs by almost one order of magnitude after one month sediment-carbon contact. Treatment efficacy increases with increasing carbon dose and decreasing carbon particle size. Similar trends are observed with the clam Corbicula fluminea and sediment from the Grasse River (near Massena, NY). Although the total PCB concentration in the two sediments is similar, Macoma in untreated Hunters Point sediment accumulated 4 to 6 times more PCBs than Corbicula in untreated Grasse River sediment. A biodynamic model was used to demonstrate that both sediment geochemistry and organism feeding strategies influenced PCB uptake by the clams. The model suggests that whereas Macoma takes up approximately 90% of its PCBs from ingested sediment particles, Corbicula's PCB uptake is more balanced between the aqueous and ingestion routes. This implies that mass transfer of PCBs from native sediment to activated carbon particles is essential for bioavailability reduction. |
