Bioaccumulation of PCB Congeners by Diporeia spp.: Kinetics and Factors Affecting Bioavailability

The toxicokinetics of four polychlorinated biphenyl (PCB) congeners were determined for the amphipod Diporeia spp. exposed to selected PCB congeners through both water and sediment to determine the effect of temperature and organism size (mass). For compounds with log K_ow 6 or greater, the water-only uptake coefficient (k_u) was inversely proportional to the size of the organism at all temperatures. For monochlorobiphenyl, k_u was directly proportional to organism mass only at 16°C. Increasing temperature resulted in increasing uptake rate coefficients for all compounds except hexachlorobiphenyl (HCBP) where k_u did not appear to depend on temperature. The hydrophobicity of the contaminants did not contribute significantly to changes in uptake rate from water. The elimination rate constant (k_e) was inversely proportional to organism size but was not significantly affected by temperature. The elimination rate constant declined exponentially with increasing log K_ow. As log K_ow increased, the effect of organism mass on k_e was greatly reduced. The uptake from sediment was affected by temperature and the congener log K_ow. At lower temperatures, the uptake coefficient from sediment (k_s) declined with increasing log K_ow, while at higher temperatures, it exhibited a slight upward trend. Smaller animals had much higher uptake rates from sediment than large or medium size animals. Small animals exhibited very high biota-sediment accumulation factors (5.4 to 20.8) over 4 to 16°C for HCBP (BSAF, concentration in the organism normalized to the lipid content divided by the concentration in the sediment normalized to the organic carbon content). The relationship between BSAF and log K_ow was exponential for both laboratory and field data.