Principal Biogeochemical Factors Affecting the Speciation And Transport of Mercury through the terrestrial environment

Abstract

It is increasingly becoming known that mercury transport and speciation in the terrestrial environment play major roles in methyl-mercury bioaccumulation potential in surface water. This review discusses the principal biogeochemical reactions affecting the transport and speciation of mercury in the terrestrial watershed. The issues presented are mercury-ligand formation, mercury adsorption/desorption, and elemental mercury reduction and volatilization. In terrestrial environments, OH-, Cl- and S- ions have the largest influence on ligand formation. Under oxidized surface soil conditions Hg(OH)2, HgCl2, HgOH+, HgS, and Hg0 are the predominant inorganic mercury forms. In reduced environments, common mercury forms are HgSH+, HgOHSH, and HgClSH. Many of these mercury forms are further bound to organic and inorganic ligands. Mercury adsorption to mineral and organic surfaces is mainly dictated by two factors: pH and dissolved ions. An increase in Cl- concentration and a decrease in pH can, together or separately, decrease mercury adsorption. Clay and organic soils have the highest capability of adsorbing mercury. Important parameters that increase abiotic inorganic mercury reduction are availability of electron donors, low redox potential, and sunlight intensity. Primary factors that increase volatilization are soil permeability and temperature. A decrease in mercury adsorption and an increase in soil moisture will also increase volatilization. The effect of climate on biogeochemical reactions in the terrestrial watershed indicates mercury speciation and transport to receiving water will vary on a regional basis.

Mercury concentrations and pools in four Sierra Nevada forest sites, and relationships to organic carbon and nitrogen

“…The relationships, however, were weak and caused by the Truckee sites with higher silt and clay contents also showing higher Hg concentrations as compared to the sandier Little Valley sites. The lack of correlation of Hg content with clay content within individual sites, however, was surprising since a recent review (Gabriel and Williamson 2004) about Hg in soils and terrestrial environment suggested that clay minerals -along with a series of oxides and metal hydroxides -play an important role as sorbent for Hg in soils. However, differences in soil texture between the Truckee and Little Valley sites may co-determine differences in retention of C, N, and Hg at the sites.…”

Behavior of mercury in a soil–plant system as affected by inoculation with the arbuscular mycorrhizal fungus Glomus mosseae

“…Several abiotic and biotic factors contribute to the conversion of Hg species in soil. Soil organic matter, in particular dissolved organic matter, has been demonstrated to mediate the nonbiological process and affect Hg speciation (Schlüter 2000), while soil microbe is considered to play a key role in the biological process of Hg reduction and methylation in soil (Gabriel and Williamson 2004).…”

Occurrence and Mobility of Mercury in Groundwater

“…Recent experiments show that Fe(II) in minerals also can reduce Hg(II) to Hg(0). For example, in sealed, dark bottles, magnetite was found to reduce Hg(II) to Hg(0) within minutes (Wiatrowski et (Gabriel & Williamson, 2004). Although metals typically bind to acid sites (carboxyls, phenols, ammonium, alcohols, and thiols) in organic matter, Hg(II) binds preferentially with thiols and other reduced sulfur groups with which it forms strong covalent-like bonds.…”