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NIEHS R01ES024344 2014-2018

Biogeochemical Framework to Evaluate Mercury Methylation Potential During in-situ Remediation of Contaminated Sediments. Heileen Hsu-Kim, Marc Deshusses Duke University Dwayne Elias Oak Ridge National Lab. NIEHS R01ES024344 2014-2018. Project team. Duke University

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NIEHS R01ES024344 2014-2018

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  1. Biogeochemical Framework to Evaluate Mercury Methylation Potential During in-situ Remediation of Contaminated Sediments Heileen Hsu-Kim, Marc Deshusses Duke University Dwayne Elias Oak Ridge National Lab NIEHS R01ES024344 2014-2018

  2. Project team Duke University Helen Hsu-Kim (PI) – Aquatic Geochemistry Marc Deshusses (Co-PI) – Bioremediation Oak Ridge National Lab Dwayne Elias (Co-PI) – Microbial Ecology Other Collaborators Steven Brown,Ph.D., Dow Chemical, Berry’s Creek Study Group

  3. Challenges of the mercury problem: • Many sources to biosphere • Long range transport • Food web accumulation • Mechanisms of MeHg production Selin, 2009, Annu. Rev. Environ. Resour. Objective: To establish biogeochemical indicators for methylmercury production potential

  4. Factors contributing towards mercury methylation potential Framework to predict methylation potential Productivity of methylating microorganisms Bioavailability of Hg ? ?

  5. Geochemical Forms of Mercury in Sediments HgHxS2x-2 Hg-thiol Hg-DOM Aggregated or micro-crystalline HgS(s) Amorphous or crystalline HgS nanoparticles DOM-capped polynuclear HgS clusters Dissolved Hg(II) complexes High methylation potential Low methylation potential

  6. Microorganisms that Methylate Mercury Gilmour et al., ES&T, 2013 Firmicutes, Clostridia • Obligate anaerobes • Phylogenically diverse • hgcAB: two gene cluster Deltaproteobacteria ARCHAEA Euryarchaeota

  7. Biomethylation in Sediment Slurry Microcosms Saline water Freshwater Ambient Hg: 2 nmol g-1 Spike Hg: 2 nmol g-1 [SO42-]0 = 15 mM [SO42-]0 < 0.07 mM dissolved Hg+sulfide dissolved Hg+sulfide nano-HgS nano-HgS microcrystalline HgS microcrystalline HgS Bioavailability-limited methylation Productivity-limited methylation Zhang et al., ES&T, 2014

  8. Bioavailability vs. Productivity Mixed microbe community enriched from sediments Dissolved Hg added Nano HgS added C-substrate for growth Threshold? Kucharzyk et al., ICMGP, 2013

  9. Project Objectives: • To establish biogeochemical indicators for methylmercury production potential • To test the effectiveness of in-situ remediation Sediment-water microcosms with samples from Superfund site Measurements of Methylation Potential Site Characterization and Remediation • Aim 1: Activity of methylating microbes • hgcAB gene abundance/expression • Microbial diversity • Aim 3: Delineation of the controls on methylation potential • Limited by microbial activity • Limited by bioavailability • Aim 4: Effects of sediment amendments • Activated carbon • Clay mineral particles • Ferrous iron (FeCl2) • Aim 2: Hg bioavailability • Size fractionation, solid-water partitioning of Hg • Thiol-extraction potential • Passive sampler with thiolated resin

  10. Activity of Methylating Microbes Amino acid sequence alignments for hgcAB for all predicted Hg-methylating organisms Design schematic for PCR, qPCR and RT-qPCR primers. Parks et al., Science, 2013 Gilmour et al., ES&T, 2013

  11. Quantification of Hg bioavailability Thiol-based selective extraction microbial culture: D. priopionicus 1pr3 dissolved Hg+sulfide nano-HgS bulk-scale HgS Zhang et al., ES&T, 2012

  12. Evaluation of Hg methylation potential in sediments Anaerobic sediment-water microcosms Data Analysis: Calibration of measurement methods • Major experimental variables: • Sediment origin • Type of Hg added (dissolved, nanoHgS, Hg-FeS) differentiated by Hg isotope • Measurements of methylation potential: • MeHg concentration or net production rate • Gene abundance & expression • Hg bioavailability (thiol selective extraction) MeHg production rate bioavailable [Hg] Field samples of benthic sediments • (Oak Ridge, TN; Berry’s Creek Study Area; other sites?) • Range of characteristics: • Salinity • Organic Carbon • MeHg concentration (relative to total Hg) hgcAB abundance or expression Assess the effectiveness of remediation

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