Emission of biogenic hydrogen sulfide

Until recently sulfur has been assumed to occur in the atmosphere principally in three forms: H₂S, SO₂ and sulfates. The principal processes by which H₂S is believed to be generated on a global scale are (1) nonspecific reduction of organic sulfur and (2) from sulfate reduction by anaerobic bacteria. Unfortunately, these assumptions have not been verified by analyses of the volatile sulfur compounds emitted by the micro-organisms that are supposed to be responsible for sulfur gas exchange in natural systems. To the contrary, gas chromatographic analyses using a flame photometric detector specific for sulfur at 394 nm indicates that dimethyl sulfide (DMS) and dimethyldisulfide (DMDS) are the major compounds in the gaseous emissions from bacteria and fresh water green and blue-green algae isolated from different soil types and eutrophic as well as naturally clean waters. Analysis of the sulfur gases in a wide variety of sea water samples and those released by red, green and brown seaweeds indicate that organic sulfur emissions dominate over H₂S. The data suggest the hypothesis that the micro-biota in the various natural systems like soil, leaf litter, lakes, ponds, rivers, and the oceans produce predominantly organic sulfides and that the reported observation of H₂S emission from water-logged soils and anaerobic muds is related to their low pH. Presumably the biogenic production of gaseous sulfur compounds constitutes a major input in the sulfur cycle. Unfortunately, the source of strength and spatial distribution of these sources are unknown.