Biogenic thiols play numerous important roles in aquatic system. While thiols are known to be sensitive to light, the photochemical transformation of thiols in natural waters remains largely unknown. This study systematically assessed the photochemical transformation of naturally abundant thiols, including cysteine (Cys), arginylcysteine (RC), γ-glutamylcysteine (γEC), glutathione (GSH), and phytochelatin (PC) in solutions containing chromophoric dissolved organic matter (CDOM). The results show that all thiols underwent rapid photochemical transformation. The transformation rates of thiols were highly pH-dependent and increased with increasing solution pH. Cys and RC show much higher transformation rates than other thiols, due to lower pKa of Cys sidechain and sorption of RC to CDOM, respectively. While all investigated pathways contributed to thiol transformation, singlet oxygen- and hydrogen peroxide-mediated oxidation was dominant in the CDOM-sensitized photodegradation of γEC, GSH, and PC. Thiol photoreactivity was not affected by complexation with Fe3+ and Ag+, slightly enhanced by complexation with Zn2+, Cd2+ and Hg2+, and significantly enhanced by complexation with Cu2+. In addition, transformation rates of thiol were also enhanced by increasing solution salinity.

Aquatic photochemical transformations of thiols with dissolved organic matter

253rd National Meeting (2017)

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