Sulfur speciation in mercury-contaminated sediments of a coastal lagoon: the role of elemental sulfur

Chemical equilibrium studies have predicted that elemental sulfur (S-o) could play a crucial role in mercury mobility in salt marsh sediments. This prompted us to consider the occurrence of S-o in conjunction with the degree of contamination in sediments of a coastal wetland (Pialassa Baiona, Italy) impacted by inputs of mercury derived from past industrial activity. The distribution of S-o, total Hg, soluble sulfates and acid-soluble sulfides was studied in five sediment cores collected in two ponds of the lagoon. Sulfides, sulfates and S-o exhibited vertical profiles typical of salt marsh systems, with concentrations declining with depth. Mercury enrichment (2-23 mg kg(-1)) was detected at the surface strata where the highest concentrations of sulfides and St) were found (up to 1.70 and 0.9 g kg(-1). respectively). The effect of elevated levels of sulfides and, elemental sulfur on the fate of mercury in the lagoon is discussed.