The role of carbonate radical in limiting the persistence of sulfur-containing chemicals in sunlit natural waters.
Carbonate radical (*CO3-) is a selective oxidant that may be important in limiting the persistence of a number of sulfur-containing compounds in sunlit natural waters. Thioanisole, dibenzothiophene (DBT), and fenthion were selected to investigate the degradation pathway initiated by *CO3-; electron-rich sulfur compounds are particularly reactive towards the *CO3-. Using HPLC, GC, GC-MS and LC-MS for structural confirmation, the major photodegradation products of thioanisole and DBT were the corresponding sulfoxides. The sulfoxide products were further oxidized through reaction with *CO3- to the corresponding sulfone derivatives. Fenthion showed a similar pathway with appearance of fenthion sulfoxide as the major product. The proposed mechanism involves abstraction of an electron on sulfur to form a radical cation, which is then oxidized by dissolved oxygen. Each of the sulfur probes were further investigated in a sunlight simulator under varying matrix conditions. The highest rate constants occurred in the *CO3- matrix, and the lowest occurred in a matrix of dissolved organic carbon (DOC) and bicarbonate. In synthetic and natural field water, thioanisole photodegraded faster than under direct photolysis, with half-lives of 75.1 and 85.8 min, respectively. Fenthion photodegraded more rapidly than thioanisole. DBT photodegraded rapidly in a *CO3- matrix with a half-life of 24.8 min, while the half-life of direct photolysis was 350 min. Photodegradation products of each compound were also investigated. Ultimately, *CO3- was found to contribute toward the photodegradation of sulfur-containing compounds in natural waters.
Huang
J
J
Department of Chemistry, University of Toronto, Ont., Canada.
Mabury
S A
SA
D002254:Carbonates / Q000737:chemistry*; D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D005284:Fenthion / Q000032:analysis / Q000737:chemistry; D005609:Free Radicals; D008401:Gas Chromatography-Mass Spectrometry; D006207:Half-Life; D015394:Molecular Structure; D016877:Oxidants; D010084:Oxidation-Reduction; D010777:Photochemistry; D013440:Sulfides / Q000032:analysis / Q000737:chemistry; D013450:Sulfones / Q000032:analysis / Q000737:chemistry; D013454:Sulfoxides / Q000737:chemistry; D013457:Sulfur Compounds / Q000032:analysis* / Q000737:chemistry*; D013472:Sunlight; D013876:Thiophenes / Q000032:analysis / Q000737:chemistry; D014873:Water Pollutants / Q000032:analysis*
D002254:Carbonates; D005609:Free Radicals; D016877:Oxidants; D013440:Sulfides; D013450:Sulfones; D013454:Sulfoxides; D013457:Sulfur Compounds; D013876:Thiophenes; D014873:Water Pollutants; C093850:methylphenylsulfide; D005284:Fenthion; C016366:dibenzothiophene