Geochemistry

Guiding Mercury's Meandering

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Science  03 Jul 2009:
Vol. 325, Issue 5936, pp. 12
DOI: 10.1126/science.325_12b
CREDIT: ISTOCK.COM

Mercury's toxicity impels wide-ranging study of the binding and redox behavior of the element under varying environmental conditions. Sulfate-reducing bacteria in soils and sediments are known to enhance mercury accumulation in higher species such as fish and humans by methylating oxidized Hg(II) ions. To what extent do geochemical reactions at mineral surfaces play a role in controlling the fate of Hg? Lee et al. uncover sharp variations in Hg(II) adsorption behavior on muscovite as they shift the local concentration of naturally abundant organic acids; complexation by the organics in free solution appeared to enhance adsorption more effectively than did a preformed film on the surface. In a related study, Wiatrowski et al. show that when Hg(II) adsorbs onto redox-active mineral surfaces such as magnetite, soluble Hg(II) is quickly reduced to highly mobile gaseous Hg(0). It remains unclear how organic layers on redox-active mineral surfaces specifically influence these and similar electron transfer reactions. Taken together, the two studies suggest that mineral-associated processes such as adsorption and phase transformation may provide stiff competition for the bacteria that catalyze Hg methylation reactions in mediating Hg fate and mobility.

Environ. Sci. Technol. 43, 10.1021/es900214e;10.1021/es9003608 (2009).

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