Bioaccumulation and differential partitioning of polychlorinated biphenyls in freshwater, planktonic food webs

The planktonic food chain phytoplankton - zooplankton - young-of-the-year roach (Rutilus rutilus) was studied in 19 lakes in southern Sweden to investigate the bioaccumulation of polychlorinated biphenyls (PCBs). The Sigma PCB concentrations did not steadily increase with increasing trophic level. The Sigma PCB concentrations in zooplankton (400 ng.g lipid(-1)) were lower than in both phytoplankton (660 ng.g lipid(-1)) and fish (890 ng.g lipid(-1)), which did not differ significantly. Lipid content explained 40% of the total variation in dry weight normalised sigma PCB concentrations in the samples. The PCBs were differentially partitioned between the trophic levels. The logBMFs (biomagnification factors, concentration in predator/concentration in prey) were a function of the logK(ow) of the PCB congeners. The logBMF(zoo/phyto) values were < 0 for all PCB congeners on a lipid weight basis, and the logBMF(fish/zoo) values were < 0 for PCB congeners with logK(ow) > 6. We conclude that no PCBs had higher lipid-normalised concentrations in zooplankton than in phytoplankton and the most lipophilic PCBs had moderately higher concentrations in roach than in zooplankton. PCBs with logK(ow) > 6 decreased in concentration from phytoplankton to zooplankton to roach. We suggest that the concept of biomagnification did not apply to the planktonic food chain investigated in these lakes.