Persistent organic pollutants (POPs) in pelagic systems

Several studies show that there are interactive processes between eutrophication and uptake of persistent organic pollutants (POPs) in aquatic biota. The main concept is that the increased biomass and production in aquatic ecosystems, due to excess discharge of nutrients, causes a chain event that results in reduced uptake of POPs in primary producers (phytoplankton). This effect is then transferred to consumers at different trophic levels. The chain event may work in an indirect way by increasing the sedimentation of organic matter and, thereby, increasing the downward flux of pollutants to the bottoms, where they are caught in the organic sediment matrix. The chain event may also work in a direct way; the uptake of POPs in the fast growing phytoplankton is decreased as a result of "growth-dilution", and lower amounts of pollutants are transported in the food-web. The effect seen may also be a result of changed food-web structures that differ considerably from nutrient-poor to nutrient-rich ecosystems. In this paper, we use the existing knowledge of POPs behavior in aquatic systems of different nutrient status, to discuss possible interactive processes of eutrophication and contaminants in the Baltic Sea. The Baltic is known to be highly contaminated with POPs and exposed to ongoing eutrophication. Results from investigations in lakes are compared to laboratory and field studies of the Baltic Sea.