Modeling PCB mass transfer and bioaccumulation in a freshwater oligochaete before and after amendment of sediment with activated carbon.

A mass transfer model is presented that couples sediment geochemistry with PCB bioaccumulation by the benthic invertebrate, Lumbriculus variegatus. This model accounts for PCB intraparticle mass transfer, desorption, and adsorption by different particle types, and uptake by the benthic invertebrates through two pathways, dermal absorption, and sediment ingestion. The biological parameters, dermal uptake coefficients, depuration rates, sediment ingestion rates, and uptake efficiencies, were measured independently. The model was evaluated by laboratory bioaccumulation experiments for three freshwater sediments that were characterized for PCB concentration, PCB desorption rate, and equilibrium partitioning behavior. The model was also tested for its ability to predict changes in PCB bioaccumulation in the three sediments after amendment with activated carbon to reduce PCB bioavailability. For most PCB congeners, the modeled results and measured values agree within a factor of 2 for all three sediments before and after treatment with activated carbon. This model broadly agrees with the experimental data and can be used to predict changes in bioaccumulation of hydrophobic organic compounds by the benthic organisms in sediments with known geochemical characteristics and under different sorbent amendment scenarios.