Spatial distribution and toxic potency of trace metals in surface sediments of the Seine estuary (France)

Due to very high anthropogenic pressures and urban waste discharge, the Seine estuary is still among the world's most polluted estuaries. The purpose of this work is to investigate the distribution of trace metals in surface sediments in order to assess to the contamination level, metal bioavailability, and ecotoxicological status. Five sites covering the salinity gradient of the estuary were chosen to evaluate the distribution and contamination level of trace metals in surface sediments. The results showed that trace metal concentration varied seasonally and spatially. Subsequently to assess the actual environmental toxicity of sediments, the Microtox® Bioassay using Vibrio fischeri was applied on aqueous extract of sediment. Calculated enrichment factors revealed that these sediments were highly polluted by mercury, cadmium, zinc, and lead. Most of pollution sources are localized upstream especially in Poses and Oissel, and the contamination levels decreased from Poses to north mudflat site. Positive values of toxicity index were detected in the upstream sediments indicating potential bioavailability of trace metals in the sediments. Sediment toxicity measured with the Microtox® test was positively correlated with toxicity index demonstrating the usefulness of the toxicity index for sediment quality assessment and possible implication of metals in sediment toxicity