Turnover of polychlorinated biphenyls in an oligotrophic and an eutrophic lake in relation to internal lake processes and atmospheric fallout

The atmospheric deposition of PCB within the catchment areas of an oligotrophic lake and an eutrophic lake in southern Sweden resulted in a flow of about 1 mg PCB.m(-2).year(-1) to the lakes. The sedimentation of the pollutants in the lakes (measured by sediment traps) was 110 and 52 mg PCB.m(-2).year(-1) for the oligotrophic and eutrophic lakes, respectively. The concentration of pollutants in plankton (separated in fractions of >150, 45-150, and 10-45 mu m) was lower than that found in the sedimenting material. This indicated that the degradation of lipid and organic carbon was higher than the release of persistent pollutants from settling particles. Higher concentrations of PCB were recorded in the phytoplankton of the oligotrophic than of the eutrophic lake and attributed to higher lipid content. The higher lipid content and the higher pollutant amounts found in the primary producers suggest a mechanism that leads to zooplankton and fish displaying high pollutant concentrations in oligotrophic ecosystems. No biomagnification for phytoplankton to zooplankton was detected. The results indicate that the major part of the persistent pollutants cycling in the lakes is due to internal lake processes.