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

Abstract

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.