Biogeochemical Framework to Evaluate Mercury Methylation Potential During

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 R 01 ES 024344 2014 -2018

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

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

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

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

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

Biomethylation in Sediment Slurry Microcosms Saline water Freshwater [SO 42 -]0 = 15 m. M [SO 42 -]0 < 0. 07 m. M Ambient Hg: 2 nmol g-1 Spike Hg: 2 nmol g-1 dissolved Hg+sulfide nano-Hg. S microcrystalline Hg. S Bioavailability-limited methylation Zhang et al. , ES&T, 2014 Productivity-limited methylation

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

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 • hgc. AB gene abundance/expression • Microbial diversity Aim 3: Delineation of the controls on methylation potential • Limited by microbial activity • Limited by bioavailability Aim 2: Hg bioavailability • Size fractionation, solid-water partitioning of Hg • Thiol-extraction potential • Passive sampler with thiolated resin Aim 4: Effects of sediment amendments • Activated carbon • Clay mineral particles • Ferrous iron (Fe. Cl 2)

Activity of Methylating Microbes Amino acid sequence alignments for hgc. AB for all predicted Hg-methylating organisms Design schematic for PCR, q. PCR and RTq. PCR primers. Parks et al. , Science, 2013 Gilmour et al. , ES&T, 2013

Quantification of Hg bioavailability Thiol-based selective extraction microbial culture: D. priopionicus 1 pr 3 dissolved Hg+sulfide nano-Hg. S bulk-scale Hg. S Zhang et al. , ES&T, 2012

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