Mercury stable isotope abundances were used to trace transport of Hg-impacted river sediment near a coal ash spill at Harriman, Tennessee, USA. δ(202)Hg values for Kingston coal ash released into the Emory River in 2008 are significantly negative (-1.78 ± 0.35‰), whereas sediments of the Clinch River, into which the Emory River flows, are contaminated by an additional Hg source (potentially from the Y-12 complex near Oak Ridge, Tennessee) with near-zero values (-0.23 ± 0.16‰). Nominally uncontaminated Emory River sediments (12 miles upstream from the Emory-Clinch confluence) have intermediate values (-1.17 ± 0.13‰) and contain lower Hg concentrations. Emory River mile 10 sediments, possibly impacted by an old paper mill has δ(202)Hg values of -0.47 ± 0.04‰. A mixing model, using δ(202)Hg values and Hg concentrations, yielded estimates of the relative contributions of coal ash, Clinch River, and Emory River sediments for a suite of 71 sediment samples taken over a 30 month time period from 13 locations. Emory River samples, with two exceptions, are unaffected by Clinch River sediment, despite occasional upstream flow from the Clinch River. As expected, Clinch River sediment below its confluence with the Emory River are affected by Kingston coal ash; however, the relative contribution of the coal ash varies among sampling sites.
The Tennessee Valley Authority Kingston coal ash spill in December 2008 deposited approximately 4.1 million m(3) of fly ash and bottom ash into the Emory and Clinch River system (Harriman, Tennessee, U.S.A.). The objective of this study was to investigate the impact of the ash on surface water and sediment quality over an eighteen month period after the spill, with a specific focus on mercury and methylmercury in sediments. Our results indicated that surface water quality was not impaired with respect to total mercury concentrations. However, in the sediments of the Emory River near the coal ash spill, total mercury concentrations were 3- to 4-times greater than sediments several miles upstream of the ash spill. Similarly, methylmercury content in the Emory and Clinch River sediments near the ash spill were slightly elevated (up to a factor of 3) at certain locations compared to upstream sediments. Up to 2% of the total mercury in sediments containing coal ash was present as methylmercury. Mercury isotope composition and sediment geochemical data suggested that elevated methylmercury concentrations occurred in regions where native sediments were mixed with coal ash (e.g., less than 28% as coal ash in the Emory River). This coal ash may have provided substrates (such as sulfate) that stimulated biomethylation of mercury. The production of methylmercury in these areas is a concern because this neurotoxic organomercury compound can be highly bioaccumulative. Future risk assessments of coal ash spills should consider not only the leaching potential of mercury from the wastes but also the potential for methylmercury production in receiving waters.
We
examined Hg stable isotope fractionation after the partial reduction
of Hg(II) to Hg(0) by the siderite and green rust of ferrous iron
minerals. The fractionation of Hg isotopes in closed-system experiments
followed an equilibrium fractionation model, with Hg(II) enriched
in heavier isotopes. The results indicated isotopic fractionation
(δ202HgII–δ202Hg0) of 2.43 ± 0.38 and 2.28 ± 0.40‰
for the siderite and green rust experiments, respectively. Experiments
were also performed to determine if the rapid attainment of isotopic
equilibrium was attributed to isotopic exchange between Hg(II) and
Hg(0). In the absence of other redox-active species, we observed that
the δ202Hg values of both Hg(0) and Hg(II) shifted
substantially toward equilibrium within minutes and evolved to constant
δ202Hg differences between the Hg(II) and Hg(0) pools.
Mixing experiments conducted in water and 10 mM NaCl yielded δ202HgII–δ202Hg0 differences of 2.63 ± 0.37 and 2.77 ± 0.70‰, respectively.
The 199Hg/198Hg and 201Hg/198Hg results were consistent with previously published experimental
and computational studies indicating the involvement of nuclear volume
effects in the observed fractionations between the mercury species.
Together, these findings suggest that rapid Hg isotopic exchange can
facilitate Hg stable isotope fractionation in Hg(II)–Hg(0)
redox systems and overprint isotopic fractionation caused by kinetic
processes.
Isotopic signatures used in the georeferencing of human remains are largely fixed by spatially distinct geologic and environmental processes. However, location-dependent temporal changes in these isotope ratios should also be considered when determining an individual's provenance and/or trajectory. Distributions of the relevant isotopes can be impacted by predictable external factors such as climate change, delocalisation of food and water sources and changes in sources and uses of metals. Using Multi-Collector Inductively-Coupled Plasma Mass Spectrometer (MC-ICP-MS) analyses of 206 Pb/ 207 Pb in tooth enamel and dentin from a population of 21 ± 1-year-old individuals born circa 1984 and isotope ratio mass spectrometry (IRMS) of d 18 O in their enamel, we examined the expected influence of some of these factors. The resulting adjustments to the geographic distribution of isotope ratios (isoscapes) found in tooth enamel and dentin may contain additional useful information for forensic identification, but the shifts in values can also impact the uncertainty and usefulness of identifications if they are not taken into account. KEY POINTS Isoscapes of 206 Pb/ 207 Pb and d 18 O used for geolocation are not static. Within a few years, the enamel and dentin of a person may exhibit measurable differences in 206 Pb/ 207 Pb even without changing locations. Changes in climatic patterns tied to rising temperatures are more significant than the direct effect of increasing temperature on d 18 O fixed in tooth bioapatite. Third molar (M3) enamel mineralisation includes material incorporated from before formal amelogenesis takes place.
The Online First version of this article unfortunately contained an error in the dimensions of LiBo fused bead shards described in the section "Lithium Borate Fusion Methods". On p. 13 of the manuscript PDF, in the sentence "Shards were generally selected based on size and shape: shards 0.5 to 1 mm in maximum dimension and exhibiting a flat surface were chosen."-the correct dimensions should be 1.0 to 5.0 mm. The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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