Toxicity effects of organosulfur compounds on anaerobic microbial metabolism

Four classes of organosulfur compounds were tested for their effects on anaerobic microbial activity as indicated by rates of lactate degradation, nitrate or sulfate reduction, and methanogenesis. Each class consisted of five to eight chemically related compounds that were added concurrently to anaerobic cultures established with an oily sludge inoculum. Effects on anaerobic activities were evaluated at different amounts of the chemicals and were concentration dependent in all cases. Thiophenes and thiols inhibited microbial activity under methanogenic conditions at greater than or equal to 5 mmol/L; the former compounds had less effect under nitrate-reducing conditions, and the latter had less effect under sulfate-reducing conditions. Thiophenic acids did not influence most microbial processes at the lower concentrations tested (less than or equal to 0.50 mmol/L). Aromatic sulfides were inhibitory to microbial activity under all three conditions at greater than or equal to 5 mmol/L and had a greater effect on electron acceptor reduction than lactate oxidation. We conclude that the inhibitory effect of organosulfur compounds on microbial metabolism could potentially influence the assessment of anaerobic biodegradation activities in either the laboratory or anoxic environments.