Interactions between eutrophication and contaminants. III. Mobilization and bioaccumulation of benzo(a)pyrene from marine sediments

A major environmental issue is to understand how eutrophication processes, such as organic enrichment and hypoxia may act on the distribution patterns and bioavailability of contaminants to benthic organisms. An experiment with sediment organic C content (control vs enriched with concentrated phytoplankton) and oxygen level (normoxia vs 2–3 mg O2 l−1) as fixed factors, and 14C-B(a)P in benthic organisms and sediment as dependent variable, was conducted for 93 days. Three species of sediment-dwelling organisms with different feeding strategies (Amphiura filiformis, Nereis diversicolor and Abra alba) were chosen. Blue mussels (Mytilus edulis), kept in separate aquaria, were exposed to the outflowing water of the microcosms. Concentration of 14C-B(a)P in the sediment surface at the end of the experiment was significantly higher in the organically enriched sediments than in the control sediments. Accumulation of 14C-B(a)P in A. filiformis and N. diversicolor was also higher in the presence of organic enrichment. Concentrations of 14C-B(a)P in M. edulis placed downstream of aquaria treated with organic matter were also higher, indicating a higher leaching of bioavailable 14C-B(a)P from the enriched sediments. Hypoxia had no significant effect on the sediment distribution and bioaccumulation of 14C-B(a)P, and there was no significant interaction between hypoxia and organic enrichment. Our results support the concept of selective feeding on labile organic matter as a major exposure route of organic contaminants in benthic organisms.