[PDF] Roles of dissolved organic matter in the speciation of mercury and methylmercury in a contaminated ecosystem in Oak Ridge, Tennessee | Semantic Scholar (2024)

Experiments examining the role of DOM across a wide sulfide gradient revealed that DOM only enhances Hg methylation under fairly low sulfide conditions (≲30 μM), conditions that favor HgS nanoparticle/cluster formation relative to dissolved HGS species.

Under anoxic dark conditions, strong interactions between reduced HA and Hg(0) are shown through thiolate ligand-induced oxidative complexation with an estimated binding capacity of ~3.5 μmol Hg/g HA and a partitioning coefficient >106 mL/g.

It is shown that under dark anoxic conditions reduced organic matter (NOM(re) simultaneously reduces and oxidizes Hg via different reaction mechanisms, which is expected to strongly influence the availability of reactive Hg and thus to have important implications for microbial uptake and methylation in anoxic environments.

Observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.

It is suggested that phy toplankton could play different roles in affecting Hg(II) methylation by the two groups of anaerobic bacteria, FeRB and SRB, and shed additional light on how phytoplankon blooms may modulate MeHg production and bioaccumulation in the aquatic environment.

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The results suggest that the negative charge of Hg(II) species reduces their availability to bacteria and may be one reason why accumulation of CH3Hg(I) is more often reported to occur in freshwater than in estuarine and marine biota.

It is shown that models that are in current use to describe the biogeochemistry of mercury and to calculate thermodynamic processes need to include a two-coordinated complexation of Hg(II) to reduced organic sulfur groups in NOM in soils and waters.

In both water types, VCFs of Hg(II) were similar for living and heat-killed cells, but the V CFs of MeHg were 1.5-5.0 times greater in living cells, suggesting an active uptake component for MeHG.

Speciation calculations based on results show that, in absence of substantial concentrations of inorganic sulfides, neutral chloro-complexes and free CH3Hg+ reach concentrations on the order of 10(-17)-10(-18) M at pH 5 in soil solutions with 3 x 10(-5) M of chloride.

The presence of higher Hg(R) concentrations than would be predicted under equilibrium conditions in UEFPC and in experiments with a NOM isolate suggests that kinetic reactions are controlling the complexation between Hg and NOM.

A novel competitive ligand exchange (CLE) technique was used to characterize Hg(II)-complexing ligands in samples collected from three municipal wastewater treatment plants, a eutrophic lake, a creek located downstream of an abandoned mercury mine, and a model water containing dissolved Suwannee River humic acid, suggesting that these extremely strong HG(ll)-complexed ligands should account for most of the dissolved Hg (II) species in municipal wastewater effluent.

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