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Issue 11, 2016
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Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries

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Abstract

Mercury (Hg) associated with coal ash is an environmental concern, particularly if the release of coal ash to the environment is associated with the conversion of inorganic Hg to methylmercury (MeHg), a bioaccumulative form of Hg that is produced by anaerobic microorganisms. In this study, sediment slurry microcosm experiments were performed to understand how spilled coal ash might influence MeHg production in anaerobic sediments of an aquatic ecosystem. Two coal ash types were used: (1) a weathered coal ash; and (2) a freshly collected, unweathered fly ash that was relatively enriched in sulfate and Hg compared to the weathered ash. These ash samples were added to anaerobic sediment slurries constructed with a relatively pristine sediment (containing 0.03 mg kg−1 Hg) and a Hg-contaminated sediment (containing 0.29 mg kg−1 Hg). The results of these experiments showed negligible net production of MeHg in microcosms with no ash and in microcosms amended with the low sulfate/low Hg ash. In contrast, slurry microcosms amended with high sulfate/high Hg ash showed increases in total MeHg content that was 2 to 3 times greater than control microcosms without ash (p < 0.001). 16S amplicon sequencing of microbial communities in the slurries indicated that the coal ash addition generally increased the relative abundance of the methylating microbial community, including sulfate-reducing bacteria and iron-reducing bacteria species that are known to be efficient methylators of Hg. The stimulation of these microorganisms was likely caused by the release of substrates (sulfate and Fe) originating from the ash. Overall, the results highlight the need to incorporate both environmental parameters and coal ash characteristics into risk assessments that guide coal ash management and disposal.

Graphical abstract: Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries

  • This article is part of the themed collection: Mercury
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Publication details

The article was received on 17 Aug 2016, accepted on 21 Sep 2016 and first published on 21 Sep 2016


Article type: Paper
DOI: 10.1039/C6EM00458J
Citation: Environ. Sci.: Processes Impacts, 2016,18, 1427-1439
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    Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries

    G. E. Schwartz, L. K. Redfern, K. Ikuma, C. K. Gunsch, L. S. Ruhl, A. Vengosh and H. Hsu-Kim, Environ. Sci.: Processes Impacts, 2016, 18, 1427
    DOI: 10.1039/C6EM00458J

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