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Chemical speciation and transformation of mercury in contaminated sediments PDF Print E-mail


Research point out nutrient rich aquatic environments as key factor for production of toxic methyl mercury.  

MCN Phd student at SLU  Andreas Drott will defend his thesis on Friday 8 May  10.00 AM   at SLU, Björken, Umeå.   Opponent will be Professor Francois M.M. Morel, Department of Geosciences, Princeton University, New Jersey, USA

Drott, Andreas (2009) Chemical speciation and transformation of mercury in contaminated sediments. Doctoral diss. Dept. of Forest Ecology and Management, SLU. Acta Universitatis agriculturae Sueciae vol. 2009:22.

Abstract

Biomagnification of mercury (Hg) in aquatic food webs occurs almost exclusively as mono-methyl Hg (MeHg). In this thesis, the influence of chemical speciation and environmental conditions on transformations of inorganic Hg (HgII) and MeHg was studied at eight sites in Sweden with Hg contaminated sediments. The source of contamination was either Hg0(l) or phenyl-Hg, and total Hg concentrations ranged between 1.0-1100 nmol g-1. The environmental conditions, e.g. salinity, temperature climate, primary productivity, redox conditions and organic matter content and quality, varied substantially among sites. The results show that MeHg production (HgII methylation) is relatively more important than MeHg degradation (demethylation) and input-output for accumulation of MeHg in contaminated surface (0-20 cm) sediments. The total Hg concentration influences MeHg production, likely by a control of the concentration of bioavailable HgII species. The most important factor determining differences in accumulation of MeHg among sites is indicated to be the availability of electron donors to methylating organisms, as a result of differences in primary production and subsequent input of organic matter to sediments. In contrast, the availability of sulphate is not indicated to limit MeHg production in the sediments studied. Within sub-sets of sites with similar properties, a great proportion of the variation in MeHg concentration is explained by the concentration of dissolved neutral HgIIsulphides [Hg(SH)2 0(aq) and possibly HgOHSH0(aq)]. MeHg degradation is influenced by ambient concentrations of MeHg and/or HgII, but the effect appears to vary among sites. It is suggested that the rate of oxidative demethylation is positively related to the concentration of dissolved MeHg-sulphides [MeHgSH(aq) and MeHgS-(aq)]. For improved risk assessment of Hg contaminated sediments, measurement of MeHg concentration and solubility is advised. It is shown that %MeHg (of total Hg) can be used as a proxy for MeHg production, across sites. It is also shown that filtration of pore water for analysis of MeHg concentrations must be done in an anoxic atmosphere to avoid oxidation artefacts.
Download PDF of thesis