INTERACTIONS BETWEEN EUTROPHICATION AND CONTAMINANTS .2. MOBILIZATIONAND BIOACCUMULATION OF HG AND CD FROM MARINE-SEDIMENTS

The availability of labile organic matter and oxygen from the bottom w ater are primary factors most likely to affect the accumulation of con taminants in benthic invertebrates. To test this hypothesis, a two-fac tor microcosm experiment was designed, Three species of sediment-dwell ing organisms were kept in sediments spiked with Hg-203 and Cd-109, Bl ue mussels were kept downstream in separate vessels, Different treatme nts were obtained by combination of two levels of organic carbon (enri ched, not enriched) with two levels of oxygen (7-9 mg l(-1) and 2-3 mg l(-1)) in the water flowing through the aquaria, After an experimenta l period of three months, gamma emission from the two isotopes were co unted in samples of sediments, porewater and biota, The results showed initial retention of a labile fraction of Cd in the carbon-enriched s ediments, Hg was retained to the same extent in all treatments and no significant loss from the sediment was observed during the experimenta l period, In the porewater, Hg was not detectable whereas the concentr ation of Cd was consistent with the levels predicted from low sulphide ion activities recorded on Ag/Ag2S electrodes and the solubility of C dS(s). Two-way ANOVA analyses revealed significant effects of carbon e nrichment on bioaccumulation of both Cd and Hg, Significant effects of oxygen level and oxygen-organic interactions were found for the bioac cumulation of Cd only. (C) 1997 Elsevier Science Ltd.