Toxicants accumulation rates and effects in Mytilus trossulus and Nereis diversicolor exposed separately or together to cadmium and PAHs

Two invertebrates, Mytilus trossulus and Nereis diversicolor, were exposed in aquaria to cadmium (50 mu g L-1) and a mixture of three- to six- ring PAHs (2 mu g L-1 each) for 2 weeks. Organisms of two species were reared in separate tanks or together in the same one. Concentrations of Cd, PAHs and activities of selected biomarkers: catalase ( CAT), glutathione S-transferase (GST) and acetylcholinesterase (AChE) were measured within 2 weeks of exposure. When reared separately, higher accumulation rates for cadmium were measured in mussels (16.4 mu g day(-1) g(-1) d.w. lipid-free tissue) than in polychaeta (0.7 mu g Cd g(-1) d.w day(-1)). When co-exposed, a difference in bioaccumulation was maintained but the accumulation rate in N. diversicolor increased to 1.0 mu g Cd g-1 d.w. day(-1) and decreased to 9.6 mu g Cd g(-1) d.w. day(-1) in M. trossulus. On the contrary, faster bioaccumulation rates of PAHs were seen in polychaeta than in mussels when exposed separately (19.3 vs 4.5 mu g PAHs day(-1) g(-1) lipid weight) than together (12.0 vs 3.1 mu g PAHs g(-1) l.w.day(-1)). Substantial changes in the bioaccumulation patterns of the different M. trossulus organs were observed when both species were reared together. Biochemical responses indicated no effect of the accumulated contaminants on AChE, enhancement of CAT in both species and depletion of GST in Mytilus. The observed differences are discussed in terms of different bioavailability of contaminants, route of uptake and detoxification mechanism, under the two modes of exposure.