Effects of sediment geochemical properties on the toxicity of copper-spiked sediments to the marine amphipod Gammarus locusta

The contribution of some sediment features, namely acid-volatile sulfide AVS. and total organic carbon TOC. in order to explain the toxicity of copper-spiked sediments was investigated. A 10-day assay with the marine amphipod Gammarus locusta was performed with three selected sediment types that consisted of different proportions of fine fractions FF. and TOC 0.5% FFr1% TOC; 25% FFr2% TOC; and 75% FFr4% TOC.. Copper toxic effects were observed for 0.5% FFr25% FF sediments when simultaneously extracted copper SEMCu. minus acid volatile sulfide SEMCuyAVS. were 0.3 and 3.4 mmolrg, respectively. However, no significant mortality was observed for 75% FF sediment even when the sulfide binding capacity was exceeded 1.1 mmolrgFSEMCuyAVSF8.9 mmolrg.. These results indicate that mortality could not be described solely as a function of the SEMCuyAVS, suggesting the presence of other binding phases in addition to AVS. Results of the normalized LC50 values to total organic carbon indicated that this component probably also interferes in the amphipod survival, although not completely. The estimated LC50 values were close 2 mg Curg C and 8 mg Curg C, respectively for 0% FF and 25% FF sediment. although there was still a fourfold difference between them. Considering that none of these sediment features by itself could fully explain copper toxicity, an attempt was made to describe G. locusta mortality as a function of simultaneous SEMCuyAVS and copper concentrations normalized to TOC. Nevertheless, the limited set of data available from this study prevented an attempt to model toxicity as a function of both of these factors. These findings reinforce the need to develop integrated models that include more than one binding phase, sulfide and organic carbon, and also other compartments of the system e.g. interstitial water. to improve current methodologies for predicting copper toxicity based on sediment geochemical features.