Photo-oxidation of arsenite in acidic waters containing Suwannee River fulvic acid: roles of 3SRFA* and hydroxyl radical

The photo-oxidation of arsenite (As(III)) in solution containing Suwannee River fulvic acid (SRFA) under the ultraviolet A (UVA) irradiation (lambda(max) = 365 nm) was studied. In a solution containing 100.0 mu g center dot L-1 As(III) and 10.0 mg center dot L-1 SRFA at pH 3.0, SRFA induced As(III) photo-oxidation by producing the triplet excited state of SRFA ((3)SRFA*) and hydroxyl radical(HO). Approximately 82% of As(III) oxidation was attributed to HO which depended strongly on HO2/O-2(-). The remaining 18% of As(III) oxidation was attributed to the direct reaction between As(III) and (3)SRFA*. The photo-oxidation of As(III) was significantly affected by solution pH. Excess SRFA inhibited As(III) photo-oxidation. The addition of a low concentration of ferric ions retarded the photo-oxidation of As(III) due to the poor photo-activity of Fe(III)-SRFA complexes. In contrast, the addition of ferric ions at high concentration greatly accelerated As(III) photo-oxidation because of the high photo-activity of Fe(III)-OH complexes. The fractions of SRFA with different molecular weight showed different oxidizing capacities under UV irradiation which was possibly related to the different contents of phenolic OH groups. The findings have important environmental implications for the photo-transformation behavior of As(III) in natural surface waters containing dissolved organic matter, especially acidic waters.

Automated summary

The photo-oxidation of arsenite in solution containing Suwannee River fulvic acid under UVA irradiation was studied. The process was induced by SRFA producing triplet excited state and hydroxyl radical, with additional factors such as pH, iron ions concentration, and SRFA molecular weight influencing the oxidation process significantly.