The mechanism and kinetics of photochemical reduction of Hg(II) were studied in aqueous solutions containing Aldrich humic acid (AHA), oxalate, or cysteine under acidic conditions (pH 2-3) using a photochemical setup composed of four UVB fluorescence lamps and a quartz tube. Hg(II) concentrations were analyzed spectrophotometrically using dithizone. Our results show that a minimum concentration of AHA (10 �M), oxalate (60 �M), or cysteine (0.5 �M) was required to find detectable Hg(II) reduction for the initial level of Hg(II) at 0.6 �M; the apparent Hg(II) reduction rates appeared to be higher in the presence of cysteine, followed by oxalate and then AHA. These results seem to favor the hypothesis that the Hg(II) photochemical reduction is probably not catalytic and suggest that secondary photo-reduction of Hg(II) and the thiol groups in humic acids may play important roles in the photo-reduction of Hg(II) in natural waters.

Photochemical reduction of aqueous divalent mercury in the presence of humic acids and UVB

243rd National Meeting (2012)

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