Effects of eutrophication on contaminant cycling in marine benthic systems

Effects of inputs of organic matter were studied on bioavailability and cyc ling of hydrophobic organic contaminants (HOCs) in benthic ecosystems of th e Baltic and Kattegat Seas. In laboratory experiments, effects of microalga e additions were studied on the bioaccumulation of HOCs (PCBs and PAHs) by the blue mussel Mytilus edulis, the brittle star Amphiura filiformis, and t he polychaete Nereis diversicolor. Contrary to the equilibrium partitioning theory, bioaccumulation was proportional to the concentrations of algae an d organic carbon. This was attributed to the high nutritional quality of th e algal organic carbon and suggests that feeding rather than equilibrium pa rtitioning governed bioaccumulation in these species. In the field, annual mass fluxes of PCBs in blue mussels and in brittle stars were estimated, as well as contaminant transfer to higher trophic levels. Our results suggest that: I) Eutrophication processes may contribute to increase HOC accumulat ion in benthic species. ii) Temporal variation in the quantity and quality of organic carbon needs to be considered when assessing contamination of be nthic systems. ill) Macrofaunal feeding activities are important for the be nthic-pelagic coupling of HOCs. iv) Bioturbation enhances the release of HO Cs from sediment to overlying water.