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Comparing modeled and measured mercury speciation in contaminated groundwater: Importance of dissolved organic matter composition Jan-Helge Richard, Cornelia Bischoff, and Harald Biester Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00500 • Publication Date (Web): 22 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016
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Environmental Science & Technology
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Comparing modeled and measured mercury
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speciation in contaminated groundwater: Importance
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of dissolved organic matter composition
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Jan-Helge Richard*, Cornelia Bischoff, Harald Biester
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Institut für Geoökologie, Abt. Umweltgeochemie, Technische Universität Braunschweig,
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Germany
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ABSTRACT
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In addition to analytical speciation, reliable Hg species modeling is crucial for predicting the
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mobility and toxicity of Hg, but geochemical speciation codes have not yet been tested for their
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prediction accuracy. Our study compares analyses of Hg species in highly Hg-contaminated
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groundwater (Hgtot: 0.02-4 µmol·L-1) at three sites with predictions of Hg speciation obtained
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from three geochemical codes (WHAM, Visual MINTEQ,
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implementation of Hg complexation by dissolved organic matter (DOM). Samples were analyzed
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for chemical composition, elemental, inorganic, and DOM-bound Hg (Hg(0), Hginorg, HgDOM).
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Hg-DOM complexation was modeled using three approaches: binding to humic/fulvic acids,
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binding to thiol-groups, or a combination of both. Results of Hg(0) modeling were poor in all
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scenarios. Prediction accuracy for Hginorg and HgDOM strongly depended on the assumed DOM
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composition. Best results were achieved when weaker binding sites, simulated by WHAMs
PHREEQC) with and without
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Environmental Science & Technology
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DOM submodel, were combined with strongly binding thiol groups. Indications were found, that
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thiol-DOM ratios in groundwater are likely to be lower than in surface water, highlighting the
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need for analytical thiol quantification in groundwater-DOM. This study shows that DOM
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quality is a crucial parameter for prediction of Hg speciation in groundwater by means of
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geochemical modeling.
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INTRODUCTION
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Mercury (Hg) is considered to be one of the most toxic contaminants, but its degree of toxicity
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depends on its speciation1.The mobility of Hg is also strongly related to speciation2, because
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different Hg compounds show different physico-chemical properties. The water solubility of Hg
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compounds ranges from practically insoluble Hg sulfide (cinnabar) (solubility:
