Kinetics and mechanism of abiotic decomposition of malodorous dimethyl disulfide under dark, oxic conditions

Abstract

Environmental contextDimethyl disulfide, a malodorous product of decomposing organic matter, can severely compromise the quality of drinking water. We studied the abiotic decomposition of dimethyl disulfide in aqueous solutions under dark, oxygenated conditions and found that the half-life varied from thousands to hundreds of thousands of years. The results indicate that in natural aquatic systems the decomposition of dimethyl disulfide is governed by other chemical, photochemical and microbial processes. AbstractThe presence of malodorous dimethyl polysulfides (DMPSs) has been documented in limnic systems as well as in tap water distribution systems. These compounds compromise the quality of drinking water. In this work, we studied kinetics and mechanisms of the decomposition reactions of the most abundant and stable DMPS, dimethyl disulfide (DMDS), in aqueous solutions in the presence of oxygen and absence of light. It was found that DMDS reacts with a hydroxyl ion and its decomposition leads to the formation of methyl mercaptan and other products. The decomposition reaction is of the first order with respect to both the concentration of DMDS and the activity of the hydroxyl ion, with an activation energy of 90±8kJmol−1. The half-life of DMDS under abiotic, dark, oxic conditions was observed to vary from thousands to hundreds of thousands of years depending on the pH and temperature. These results indicate that DMDS is decomposed by other chemical, photochemical and microbially-mediated pathways.