Effects of ano×ia and sulfide on concentrations of total and methyl mercury in sediment and water in two Hg-polluted lakes

Abstract

Between May and December 1996, monthly samples of surface sediment (0-1 cm), settling matter, and water were taken at a shallow site and a deep site in each of two consecutive Hg-polluted riverine lakes. In the upper lake, the sediment was polluted also with cellulose fiber. Both hypolimnia turned anoxic, but sulfide was detected only in the upper lake. When sulfide appeared, hypolimnetic methyl mercury (MeHg) increased and reached 47 pM (9.4 ng·L -1 ), whereas MeHg in the sediment below decreased. The increase in hypolimnetic inorganic Hg (IHg = total Hg -MeHg), which reached a peak of 40 pM (8.0 ng·L -1 ), was slower, possibly because mobilized IHg was methylated. In the lower lake, hypolimnetic MeHg and IHg increased less dramatically during summer stratification, reaching only 5 and 24 pM (1.0 and 4.8 ng·L -1 ), respectively. There was no detectable concomitant decrease in sediment MeHg. In both lakes, MeHg appeared to increase simultaneously with total Fe and Mn in the hypolimnion, as did IHg in the lower lake. Our observations suggest that the presence of hydrous ferric and manganese oxides decreased the mobility of Hg in both lakes but increased MeHg production in the upper lake.

Tracing the Metal Pollution History of the Tisza River Through the Analysis of a Sediment Depth Profile

“…Factor 3 also groups a number of elements and compounds, such as Hg, methylmercury and sulphides, that are interrelated by natural processes occurring in reduced environments. Methylation of Hg is controlled by the activity of sulphate-reducing bacteria also producing sulphides, as already reported for different areas (Baeyens et al 1998;Regnell et al 2001). Besides the natural formation of sulphides in reducing environments, sulphide-bearing minerals from mining activities are also transported as suspended matter in the Tisza River (Osan et al 2002(Osan et al , 2007.…”

Mercury Methylation by Planktonic and Biofilm Cultures of Desulfovibrio desulfuricans

“…The extracellular speciation of heavy metals has been demonstrated to be an important determinant of its biological uptake (). So far it has been shown that passive diffusion is a key mechanism for Hg uptake by Hg methylating bacteria in both lab culture work ( 15−17 , 23 ) and fieldwork ( − ) because of the stronger bioavailability of small-size neutral-charged Hg complexes. Comparisons of diffusion rates through the aqueous unstirred layer and through the cell membrane show a difference of several orders of magnitude, indicating that the latter is the limiting step of Hg transport to cells ( , ).…”