Effects of organic enrichment and burrowing activity of the polychaete Neries diversicolor on the fate of tetrachlorobiphenyl in marine sediments

The effects of organic enrichment and burrowing activity of the infaunal po lychaete Nereis (Hediste) diversicolor on the distribution of C-14-3,3',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 biot urbation (presence or absence of N. diversicolor) as fixed factors and conc entration of TCB in sediment, water, and biota as dependent variables allow ed us to test the four combinations. Release of TCB from the sediment to th e water column was measured in the outflowing water of the aquaria. After 2 8 d of exposure, TCB concentrations were measured in animals, feces, sedime nt cores, burrows, sediment surface, and in sulfur bacteria mats. Both biot urbation and organic enrichment enhanced the release of TCB from the sedime nt to the water column. The greatest effect was caused by the combination o f the two factors, which increased release rates by 280% compared with cont rols. No general downward transport and vertical redistribution of TCB in t he sediment were observed. However, TCB concentrations were significantly h igher in the burrow linings of the worms than in the bulk sediment. Increas ed TCB accumulation by the animals was observed following organic enrichmen t, which was considered to be the result of selective feeding on TOC-rich c ontaminated food particles. The organic enrichment also stimulated the prod uction of sulfur bacteria mars, which were found to accumulate high TCB con centrations. Our results contradict those of several other studies that hav e reported a reduced bioavailability of organic contaminants with increasin g sedimentary organic carbon content. Our study suggests that the quality o f the organic matter should be considered in the evaluation of exposure in benthic organisms.