LAKE PRODUCTIVITY AND WATER CHEMISTRY AS GOVERNORS OF THE UPTAKE OF PERSISTENT POLLUTANTS IN FISH

Factors influencing uptake and levels of persistent pollutants (PCBs, p,p'-DDE) were investigated in 341 northern pike from 61 lakes in southern Scandinavia. Although the inflow of pollutants from the atmosphere was similar throughout the area studied, large differences in levels of PCBs and DDE in predatory fish were found between lakes. The factors primarily responsible for this variation appeared to be lake trophic status and content of humic substances. Levels of persistent pollutants in the fish decreased as productivity increased. Contents of total phosphorus and chlorophyll alpha and lake water transparency (mainly influenced by phytoplankton biomass) were used as productivity indicators. The reasons for the lower levels of pollutants in fish in lakes of increasing productivity were higher growth rate of pike and higher turnover time and sedimentation of particles (phytoplankton) to which the pollutants are adsorbed. Levels of persistent pollutants decreased as the amount of humic substances (water color) increased, apparently because humus adsorbs persistent pollutants, rendering them less available for uptake in fish. The results show that it should be possible to predict levels of persistent pollutants in fish, based on the productivity and chemical properties of the lake.