Environmentally relevant precursors of carbonyl sulfide in aquatic systems

Seawater solutions of environmentally relevant organosulfur compounds, commercial humic acid (HA), and natural dissolved organic matter (DOM) were incubated with and without UV light in order to determine the carbonyl sulfide (COS) producing capabilities of these compounds. COS dark- and photo-production rate constants were determined for dilute solutions of the organosulfur compounds (μmol l−1) and HA/DOM (mg l−1). Dissolved COS was determined using a purge and cryogenic trap method followed by GC/FPD detection. COS was produced in considerable amounts both non-photochemically and photochemically from the reduced form of free acid of glutathione (GSH) and photochemically from cysteine (CYS). Other organosulfur compounds yielded little or no COS. Photosensitizers, such as commercial HA and natural DOM, photo-catalyzed COS production from several of the chemicals tested and from unknown COS precursors in the seawater samples. HA itself was found to contain COS precursors. We propose that reactions of thiyl radicals with carbonyl compounds play an important role in COS formation from the organosulfur compounds studied.