A Theoretical Study of Abiotic Methylation Reactions of Gaseous Elemental Mercury by Halogen-Containing Molecules

Abstract

Methylation reactions of gaseous elementary mercury by halogen containing molecules such as halogenomethane species CH(3)X (with X = Cl, Br, and I) and the dimethylchlorinium ion CH(3)ClCH(3)(+) were investigated at the density functional level. With CH(3)X, the reaction is predicted to be almost athermic and kinetically demanding for a thermal reaction. The reaction can proceed photochemically in the visible range; therefore sunlight may increase the reaction rate. These results compare well with the experimental data. Consecutive methylation of the CH(3)HgX products (with X = Cl, Br, and I) and subsequent formation of CH(3)HgCH(3) were also studied. These reactions are predicted to be kinetically inaccessible and thermodynamically unfavorable. With CH(3)ClCH(3)(+), the reaction is predicted to be athermic but kinetically easy. This is due to the suitability of the methyl transfer reagent. Geometrical and electronic data were systematically analyzed in order to rationalize the results.

ICP-MS/MS as a tool to study abiotic methylation of inorganic mercury reacting with VOCs

“…The lipophilic nature of CH 3 Hg enhances its ability to be bioaccumulated compared with inorganic Hg, and results in enhanced biomagnication of CH 3 Hg in the food chain. Although Hg 0 is the dominant mercury species in the troposphere, the methylation productivity of Hg 0 is low, [17][18][19] perhaps attributed to the low reaction activity of Hg 0 . Biotic methylation was shown to be carried out by sulfate-reducing bacteria, 2,3 iron-reducing bacteria, 4 or other microbes.…”

“…However, little information has been reported on the abiotic methylation of atmospheric mercury. Although Hg 0 is the dominant mercury species in the troposphere, the methylation productivity of Hg 0 is low, [17][18][19] perhaps attributed to the low reaction activity of Hg 0 . Nevertheless, mercury ions with higher reaction activity also exist in the atmosphere, 20,21 with ion content in the magnitude of pg m À3 .…”