Environmental Science


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Science  06 Jan 2012:
Vol. 335, Issue 6064, pp. 14
DOI: 10.1126/science.335.6064.14-b

In aquatic or subsurface environments, sulfate-reducing bacteria mediate the transformation of inorganic divalent mercury into highly toxic, bio-available methylmercury (MeHg), but it is unclear how this reaction depends on the phase of the Hg(II). Zhang et al. examined the degree to which sulfate-reducing bacteria methylated three forms of Hg(II), representing different size fractions and different states of aging: dissolved Hg(II) ions, 3- to 4-nm-diameter HgS nanoparticles, and >500-nm HgS particles. The bacteria methylated dissolved Hg(II) fastest, but there were also significant differences between nanoparticles and larger particles of HgS that were attributed to size-dependent crystallinity differences and not simply the amount of reactive surface area. Furthermore, aging HgS nanoparticles—which transformed them into larger HgS particles over time—resulted in less MeHg formation as well, suggesting that methylation is related to the intermediate Hg(II) phases present and the crystal growth kinetics. These observations may help explain the varying production rates of MeHg in the environment.

Environ. Sci. Technol. 10.1021/es203181m (2011).

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