Sulfate methyl mercury production

There is a link between sulfate levels and methyl mercury production in wetland ecosystems (Figure 11.12). High sulfate levels (or salinity levels) inhibit methylation whereas methylation increases when the sulfate levels are low. The increased sulfide formation at high sulfate levels actually inhibits the MeHg production. The sulfide produced reacts with mercury to form HjS and makes mercury less available for the sulfate-reducing bacteria, which methylate the mercury present in wetland soils. 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

The hydroboration/oxidation sequence is complementary to the direct, mercury(ll)-catalyzed hydration reaction of a terminal alkyne because different products result. Direct hydration with aqueous acid and mercury(IJ) sulfate leads to a methyl ketone, whereas hydroboration/oxidation of the same terminal alkyne leads to an aldehyde. 

The ability of sulfate-reducing bacteria to methylate inorganic mercury depends on sulfide-to-sulfate ratios sulfate concentrations less than 1 mg L starves sulfate-reducing bacteria and thus inhibits methylation. Sulfate concentration greater than 20 mg L will result in excess sulfide production, which will also inhibit mercury methylation. 

Desulfovibrio spp. High sulfate levels inhibit methylation while methylation is increased when sulfate levels are low and concentrations of organic fermentation products are high. Sulfide generated by sulfate-reducing bacteria inhibits mercury methylation by rendering mercury less available for methylation. 

Mercury accumulation by two species of freshwater teleosts eastern mosquitofish (Gambusia holbrookv, lake chubsucker, Erimyzon sucetta) in an artificial wetland ecosystem was sigifificantly enhanced by sulfate addition. Authors conclude that sulfate additions result in elevated production of methylmercury in sediment and porewater -possibly due to increased mercury methylation by sulfate-reducing bacteria - which is readily evident in fish and water with subsequent increases through the food web. 

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