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

Chemical equilibrium studies have predicted that elemental sulfur (S0) could play a crucial role in mercury mobility in salt marsh sediments. This prompted us to consider the occurrence of S0 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 S0, total Hg, soluble sulfates and acid-soluble sulfides was studied in five sediment cores collected in two ponds of the lagoon. Sulfides, sulfates and S0 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 S0 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.