Relationship of Sediment Redox Conditions to Methyl Mercury in Surface Sediment of Louisiana Lakes

Abstract

Surface sediment from three Louisiana Lakes containing overlying water layer spiked with 2 microg/g (2 ppm) mercury were incubated under oxygenated (air) and nonoxygenated (N2) conditions for determining the impact of oxygen status of overlying water on methylation of Hg in surface sediment from these lakes. The added mercury resulted in a greater than ten fold increase in methyl mercury (MeHg) as compared to native concentration of MeHg. The increase in methyl Hg production was less in sediment in which overlying water was exposed to oxygen rather than nitrogen. Results suggest that methyl Hg production would be less in lakes containing an oxygenated water column. In parallel microcosm studies without added mercury. MeHg decreased in sediment when redox potential of sediment suspension was increased from -200mV to +50mV. Results of these studies demonstrate the importance of oxygenation or redox condition of surface sediment on mercury methylation and demethylation. Sediment conditions, which either reduce methylation or enhance demethylation in surface sediment, will limit the bioavailability of MeHg to the aquatic environment.

Influence of a wastewater treatment plant on mercury contamination and sediment characteristics in Vidy Bay (Lake Geneva, Switzerland)

“…Therefore, Hg in the solid phase, having reached the sediments, can be buried, resuspended, released or even methylated, making sediments a sink and a source of Hg (Blasco et al 2000;Bale 2000). Methylation occurs primarily, but not exclusively, in anoxic waters and sediments (DeLaune et al 2004). It is carried out by some species of bacteria belonging to the groups of sulphate-(SRB) and iron-reducing bacteria (IRB) (Compeau and Bartha 1985;Gilmour and Henry 1991;Gilmour et al 1992;Pak and Bartha 1998;Kerin et al 2006;Fleming et al 2006;Hamelin et al 2011;Parks et al 2013).…”

Predicting mercury concentrations and fluxes in the water column and sediment of lakes with a limited dataset

“…This phenomenon, resulting in anaerobic conditions at the sediment surface and lowered redox potentials (-ve), has been suggested to be a requirement for MeHg formation (related to MeHg:THg ratio) in lakes [34]. On the contrary, Regnell and Ewald [35] found that sediment MeHg levels decreased during summer stratification in the pelagic region until August before eventually increasing again.…”

“…Seasonal stratification typically occurs in lakes that exceed a maximum depth of 5 m, although large variations exist in depth of thermocline formation from lake to lake (2 m to more than 20 m, especially in clear and transparent southern lakes) [33]. This phenomenon, resulting in anaerobic conditions at the sediment surface and lowered redox potentials (-ve), has been suggested to be a requirement for MeHg formation (related to MeHg:THg ratio) in lakes [34]. On the contrary, Regnell and Ewald [35] found that sediment MeHg levels decreased during summer stratification in the pelagic region until August before eventually increasing again.…”

The dependence of the methylation of mercury on the landfill stabilization process and implications for the landfill management

“…The higher MMHg concentrations and the MMHg ratio at A1 compared with that of S1 can be ascribed to the low ORP in the anaerobic landfill. Under aerobic conditions, the activity of SRB was reduced and the demethylation of MMHg was accelerated, resulting the lower production and stability of MMHg (Olson and Cooper, 1976;Delaune et al, 2004;Bridou et al, 2011).…”