Arsenic in marina sediments from the Mediterranean coast: speciation in the solid phase and occurrence of thioarsenates

Abstract : Arsenic speciation was determined in marina sediments of the French Mediterranean coast. The sediment from L'Estaque marina was highly impacted by both metallurgical activities and by the commercial port of Marseille, in contrast to the sediment from St Mandrier marina that was less polluted. In the solid phases, As(III) was the dominant species in L'Estaque sediment, whereas As(V) was the main form in St Mandrier sediment, with total As concentrations in the range 160-350 mg/kg and 17-20 mg/kg respectively. In both sites, arsenic was the major trace element detected in interstitial water, its concentration reaching values higher than 1 mg/L in L'Estaque sediment. Sulfate-reduction seemed to be more active in L'Estaque site, probably because of the availability of easily biodegradable organic matter. This condition favored the formation of thioarsenates that were quantified here for the first time in a polluted marine sediment. Thioarsenates represented 69 ± 24% of total dissolved As in the 15-60 cm depth sediment layer. Our results suggest that bacterial activity may significantly contribute to increase arsenic solubility and mobility in harbor sediments, where crude oil input stimulates sulfate-reducers.