title: Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries.
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-1Hg) and a Hg-contaminated sediment (containing 0.29 mg kg-1Hg). 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.
authors.affiliation: Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA. hsukim@duke.edu.
authors.forename: Grace E
authors.initials: GE
authors.lastname: Schwartz
authors.affiliation: Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA. hsukim@duke.edu.
authors.forename: Lauren K
authors.initials: LK
authors.lastname: Redfern
authors.affiliation: Iowa State University, Department of Civil, Construction, and Environmental Engineering, Ames, Iowa 50011, USA.
authors.forename: Kaoru
authors.identifier: http://orcid.org/0000-0003-3715-7821
authors.initials: K
authors.lastname: Ikuma
authors.affiliation: Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA. hsukim@duke.edu.
authors.forename: Claudia K
authors.initials: CK
authors.lastname: Gunsch
authors.affiliation: University of Arkansas-Little Rock, Department of Earth Sciences, Little Rock, Arkansas 72204, USA.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Ruhl
authors.affiliation: Duke University, Division of Earth and Ocean Sciences, Nicholas School of the Environment, Durham, North Carolina, USA.
authors.forename: Avner
authors.initials: A
authors.lastname: Vengosh
authors.affiliation: Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708, USA. hsukim@duke.edu.
authors.forename: Heileen
authors.identifier: http://orcid.org/0000-0003-0675-4308
authors.initials: H
authors.lastname: Hsu-Kim
mesh_terms: D001421:Bacteria, Anaerobic / Q000378:metabolism*; D060729:Coal Ash / Q000009:adverse effects* / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology*; D008767:Methylmercury Compounds / Q000378:metabolism*; D064307:Microbiota; D013431:Sulfates / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000009:adverse effects* / Q000378:metabolism
chemical_list: D060729:Coal Ash; D008767:Methylmercury Compounds; D013431:Sulfates; D014874:Water Pollutants, Chemical