Diel mercury concentration variations in a mercury-impacted stream.

Filtered and particulate mercury (Hg) and methylmercury (MMHg), and associated water chemistry parameters, were evaluated bi-hourly for several 30 h periods during the summer and winter seasons at several distinct locations (downstream forested, midstream urban/suburban, upstream industrial) along a creek contaminated with high levels of inorganic Hg to determine if biogeochemical Hg and MMHg cycles respond to the daily photocycle. In summer particulate Hg and MMHg concentrations doubled overnight (excluding the upstream industrial site) concurrent with increases in turbidity and total suspended sediment; no such pattern was evident in winter. Seasonal and diel changes in the activity of macrobiota affecting the suspension of contaminated sediments are likely responsible for these patterns as other potential explanatory variables (, instrument drift, pH, discharge) could not account for the range and timing of our observations.

Determining the Reliability of Measuring Mercury Cycling Gene Abundance with Correlations with Mercury and Methylmercury Concentrations.

Methylmercury (MeHg) is a bioaccumulative toxic contaminant in many ecosystems, but factors governing its production are poorly understood. Recent work has shown that the anaerobic microbial conversion of mercury (Hg) to MeHg requires the Hg-methylation genes and that these genes can be used as biomarkers in PCR-based estimators of Hg-methylator abundance. In an effort to determine reliable methods for assessing abundance and diversity and linking them to MeHg concentrations, multiple approaches were compared including metagenomic shotgun sequencing, 16S rRNA gene pyrosequencing and cloning/sequencing gene products.

Hg isotopes reveal in-stream processing and legacy inputs in East Fork Poplar Creek, Oak Ridge, Tennessee, USA.

Natural abundance stable Hg isotope measurements were used to place new constraints on sources, transport, and transformations of Hg along the flow path of East Fork Poplar Creek (EFPC), a point-source contaminated headwater stream in Oak Ridge, Tennessee. Particulate-bound Hg in the water column of EFPC within the Y-12 National Security Complex, was isotopically similar to average metallic Hg(0) used in industry, having a mean δ202Hg value of -0.42 ± 0.

Formation of Soluble Mercury Oxide Coatings: Transformation of Elemental Mercury in Soils.

The impact of mercury (Hg) on human and ecological health has been known for decades. Although a treaty signed in 2013 by 147 nations regulates future large-scale mercury emissions, legacy Hg contamination exists worldwide and small-scale releases will continue. The fate of elemental mercury, Hg(0), lost to the subsurface and its potential chemical transformation that can lead to changes in speciation and mobility are poorly understood.

The effects of a stannous chloride-based water treatment system in a mercury contaminated stream.

We assessed the impacts of an innovative Hg water treatment system on a small, industrially-contaminated stream in the southeastern United States. The treatment system, installed in 2007, removes Hg from wastewater using tin (Sn) (II) chloride followed by air stripping. Mercury concentrations in the receiving stream, Tims Branch, decreased from >100 to ∼10 ng/L in the four years following treatment, and Hg body burdens in redfin pickerel (Esox americanus) decreased by 70% at the most contaminated site.

Characterization of soils from an industrial complex contaminated with elemental mercury.

Historical use of liquid elemental mercury (Hg(0)l) at the Y-12 National Security Complex in Oak Ridge, TN, USA, resulted in large deposits of Hg(0)l in the soils. The fate and distribution of the spilled Hg(0) are not well characterized. In this study we evaluated analytical tools for characterizing the speciation of Hg in the contaminated soils and then used the analytical techniques to examine the speciation of Hg in two soil cores collected at the site.

Role of morphological growth state and gene expression in Desulfovibrio africanus strain Walvis Bay mercury methylation.

The biogeochemical transformations of mercury are a complex process, with the production of methylmercury, a potent human neurotoxin, repeatedly demonstrated in sulfate- and Fe(III)-reducing as well as methanogenic bacteria. However, little is known regarding the morphology, genes, or proteins involved in methylmercury generation. Desulfovibrio africanus strain Walvis Bay is a Hg-methylating δ-proteobacterium with a sequenced genome and has unusual pleomorphic forms.

Bacterial growth phase influences methylmercury production by the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132.

The effect of bacterial growth phase is an aspect of mercury (Hg) methylation that previous studies have not investigated in detail. Here we consider the effect of growth phase (mid-log, late-log and late stationary phase) on Hg methylation by the known methylator Desulfovibrio desulfuricans ND132. We tested the addition of Hg alone (chloride-complex), Hg with Suwannee River natural organic matter (SRNOM) (unequilibrated), and Hg equilibrated with SRNOM on monomethylmercury (MMHg) production by ND132 over a growth curve in pyruvate-fumarate media.

Mercury reduction and complexation by natural organic matter in anoxic environments.

Mercuric Hg(II) species form complexes with natural dissolved organic matter (DOM) such as humic acid (HA), and this binding is known to affect the chemical and biological transformation and cycling of mercury in aquatic environments. Dissolved elemental mercury, Hg(0), is also widely observed in sediments and water. However, reactions between Hg(0) and DOM have rarely been studied in anoxic environments.

Kinetic controls on the complexation between mercury and dissolved organic matter in a contaminated environment.

The interaction of mercury (Hg) with dissolved natural organic matter (NOM) under equilibrium conditions is the focus of many studies but the kinetic controls on Hg-NOM complexation in aquatic systems have often been overlooked. We examined the rates of Hg-NOM complexation both in a contaminated Upper East Fork Poplar Creek (UEFPC) in Oak Ridge, Tennessee, and in controlled laboratory experiments using reducible Hg (Hg(R)) measurements and C(18) solid phase extraction techniques. Of the filterable Hg at the headwaters of UEFPC, >90% was present as Hg(R) and this fraction decreased downstream but remained >29% of the filterable Hg at all sites.

Influence of dissolved organic matter on the complexation of mercury under sulfidic conditions.

The complexation of Hg under sulfidic conditions influences its bioavailability for microbial methylation. Neutral dissolved Hg-sulfide complexes are readily available to Hg-methylating bacteria in culture, and thermodynamic models predict that inorganic Hg-sulfide complexes dominate dissolved Hg speciation under natural sulfidic conditions. However, these models have not been validated in the field.