Aquatic Sciences Meeting, Albuquerque 2001

SS02 Photochemical Reactions In Surface Waters: A Major Issue in the 21st Century? (Environmental Connections)

Date: Thursday, February 15, 2001, Time: 4:15:00 PM

Location: San Miguel

Khwaja, A, R, University of Minnesota, Minneapolis, USA, khwa0002@tc.umn.edu

Hines, N, , University of Minnesota, Minneapolis, USA, neal@mailandnews.com

Brezonik, P, L, University of Minnesota, Minneapolis, USA, brezo001@umn.edu

INFLUENCE OF AQUATIC HUMIC SUBSTANCES ON PHOTOCHEMICAL TRANSFORMATIONS OF MERCURY

Photochemistry plays a key role in Hg cycling, and interactions between Hg forms and aquatic humus (AH) affect rates of several Hg reactions. We found that methylmercury (MeHg) photolyzes by direct and indirect mechanisms. The latter proceeds via hydroxyl radicals (OH), with which MeHg reacts at near diffusion-controlled rates. AH affects these processes by absorbing light (decreasing the depth of the photic zone), scavenging OH, and directly generating OH by absorbing light. Based on lab and field studies, we describe the relative importance of direct and indirect photolysis for MeHg, reaction products, and the relative importance of the three roles of AH. AH also photo-reduces Hg(II) to Hg(0). The reduction mechanism was studied using model organic compounds with functional groups found in AH, including carboxylate, phenolic, thiol, and quinones, to evaluate the source of Hg(II) reducing power. Hg(0) was formed in a Minnesota bog lake in daylight but not in the dark. Production was faster in samples spiked with Hg(II) than at ambient Hg levels, suggesting that Hg(II) forms photo-resistant organic complexes in water.

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Aquatic Sciences Meeting, Albuquerque 2001

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