Decomposability of Some Organic Sulfur Compounds in Soil

Various organic sulfur compounds decomposed at different rates in soil under aerobic conditions. The sulfur was released rapidly from some compounds (mostly of natural origin) but only in negligible amounts from others. As estimated by formation of sulfate, the following compounds decomposed rapidly: cystine, taurine, sodium taurocholate, sulfosalicylic acid, and formaldehyde-sodiumsulfoxylate. Decomposition of the last compound may have been non-biological, at least in part. Thiamine decomposed slowly and there was slight decomposition of thiourea. There was no evidence of decomposition of the following: sulfanilic acid, sulfanilamide, sulfathiazole, sulfapyridine, mercaptoethanol, sodium diethyl-dithiocarbamate, an alkyl-aryl-sulfonate, p-thiocresol, 2-mercaptobenzothiazole, sulfonmethane, phenyl thiourea, potassium ethyl xanthate, and ammonium sulfamate. Decomposition of the organic sulfur compounds as determined by sulfate production was not related to any type of sulfur linkage. Decomposition of methionine was markedly different from that of the other sulfur compounds in that sulfate was not an end product. The sulfur was recovered as the volatile sulfur products methylthiol and dimethyl disulfide. The results indicate that the methylthiol was produced first and that the dimethyl disulfide arose from oxidation of methylthiol. The abundance of soil microorganisms increased in the soils to which those organic compounds were added from which sulfate was formed. Thiourea, phenyl thiourea, and mercaptoethanol were toxic to the soil population at the concentrations of 1% or more that were used. Decomposition of cystine, taurine, formaldehydesodium-sulfoxylate, thiamine, and sulfosalicylic acid resulted in an increase in acidity due to the formation of sulfate and, probably also in some cases, of nitrate. There was little reaction change from sodium taurocholate. With methionine the reaction became first alkaline and then somewhat acid.