Improved estimates of PCB Bioaccumulation Factors for Algae and Zooplankton Using Passive Sampling

Uptake of polychlorinated biphenyls (PCBs) by fish is controlled by the concentration in the diet and the freely dissolved concentration in the water moving across the gills. PCBs in the fish diet are also related to overlying and porewater concentrations as the organisms at the base of pelagic and benthic food webs are often close to equilibrium with water, described by compound specific bioaccumulation factors (BAF). Numerous past studies have focused on developing correlations between BAF and the octanol-water partition constant (KOW) for small pelagic organisms such as algae and zooplankton. These studies on BAF generally demonstrate a strong correlation with compound hydrophobicity for the mid and lower chlorinated PCBs and unclear relationship for the higher chlorinated compounds. We hypothesize that past studies on BAF may have been impacted by overestimation of freely dissolved concentration for higher chlorinated PCBs. We show here through laboratory mesocosm studies that a linear correlation with KOW extends to the higher chlorinated compounds (log KOW>6.5) as well when the freely dissolved concentration is measured accurately using passive sampling. For algae, the slope of the fitted line to the log bioconcentration factor (BCF) -log Kveg-oil data was closer to unity and the intercept was smaller than that of log BCF- log KOW fitted line indicating vegetable oil as a better surrogate for partitioning to algae. Results from this work can be helpful in fine tuning parameters used in food web models especially when accurately measured freely dissolved concentrations are used.