Arsenic in Marina Sediments from the Mediterranean Coast: Speciation in the Solid Phase and Occurrence of Thioarsenates

Arsenic speciation was determined in marina sediments of the French Mediterranean coast. The sediment from LEstaque 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 the LEstaque sediment, whereas As(V) was the main form in the St. Mandrier sediment, with total As concentrations in the range 160-350mg/kg and 17-20mg/kg, respectively. In both sites, arsenic was the major trace element detected in interstitial water, its concentration reaching values higher than 1mg/L in the LEstaque sediment. Sulfate-reduction seemed to be more active in the LEstaque 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 15-60cm depth sediment layer. Our results suggest that bacterial activity may significantly contribute to increased arsenic solubility and mobility in harbor sediments, where crude oil input stimulates sulfate-reducers.