FORMATION OF VOLATILE SULFIDES IN FRESH-WATER ENVIRONMENTS

Organic Volatile Sulfides (OVS) of biogenic origin are ubiquitous in the environment and are an important contributor to the global atmospheric sulfur cycle. We show that OVSs are widespread in the freshwater environment. The species H2S, COS, CS2, methanethiol (MeSH), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) have been found in samples of freshwater and in freshwater algal cultures. A few C2-C4 alkylated sulfur species were found, of which only 1-propanethiol was identified, but they were detected in less than 10% of the samples or cultures. No sulfide species predominates in freshwaters, unlike the case of DMS in marine waters. Freshwater algal cultures were grown under laboratory conditions using various sulfur sources and methyl donors. Sulfate concentrations did not influence the production of OVS, but L-methionine was key in the production of methylated sulfides. The other sulfur-containing amino acids (cysteine, cystine) did not influence the production of OVS. Methyl donors did not significantly affect OVS production, except for CH3I, Which induced higher levels of methylated sulfides with Oscillatoria sp. We did not find any factor that affected the production of H2S, COS and CS2.