Effects of organic enrichment and burrowing activity of the polychaeteNeries diversicoloron the fate of tetrachlorobiphenyl in marine sediments

The effects of organic enrichment and burrowing activity of the infaunal polychaete Nereis (Hediste) diversicolor on the distribution of 14C-3,3′,4,4′-tetrachlorobiphenyl (TCB) were studied in an experimental benthic system. Organic enrichment of the sediment was provided by a mixture of the diatom Skeletonema costatum and the sea lettuce Ulva lactuca. Organic matter and TCB were both initially added to a surface sediment layer of the microcosms. A factorial design with organic enrichment (control vs enriched) and bioturbation (presence or absence of N. diversicolor) as fixed factors and concentration of TCB in sediment, water, and biota as dependent variables allowed us to test the four combinations. Release of TCB from the sediment to the water column was measured in the outflowing water of the aquaria. After 28 d of exposure, TCB concentrations were measured in animals, feces, sediment cores, burrows, sediment surface, and in sulfur bacteria mats. Both bioturbation and organic enrichment enhanced the release of TCB from the sediment to the water column. The greatest effect was caused by the combination of the two factors, which increased release rates by 280% compared with controls. No general downward transport and vertical redistribution of TCB in the sediment were observed. However, TCB concentrations were significantly higher in the burrow linings of the worms than in the bulk sediment. Increased TCB accumulation by the animals was observed following organic enrichment, which was considered to be the result of selective feeding on TOC-rich contaminated food particles. The organic enrichment also stimulated the production of sulfur bacteria mats, which were found to accumulate high TCB concentrations. Our results contradict those of several other studies that have reported a reduced bioavailability of organic contaminants with increasing sedimentary organic carbon content. Our study suggests that the quality of the organic matter should be considered in the evaluation of exposure in benthic organisms.