DEVELOPMENT OF IN-SITU MERCURY REMEDIATION APPROACHES BASED ON METHYLMERCURY BIOAVAILABILITY Upal Ghosh and James Sanders, Department of Chemical, Biochemical, and Environmental Engineering, UMBC Cynthia Gilmour Smithsonian Environmental Research Center Dwayne Elias University of Tennessee/ Oak Ridge National Laboratory Clu-In webinar: Biogeochemical Factors Impacting in situ Remediation Metals and PAH mixtures Feb 2, 2015

RESEARCH BACKGROUND Activated carbon amended to surficial sediments reduces uptake of bioaccumulative pollutants in the food chain through: Reduced porewater concentrations Reduced bioaccumulation in benthic organisms Reduced flux into water column and uptake in the pelagic food web. Demonstrated for PCBs in several pilot studies Q: Can AC or biochar sequester Hg/MeHg and reduce bioavailability? See Feature Article : In-situ sorbent amendments: A new direction in contaminated sediment management. Ghosh et al. Environ. Sci. Technol. 45, 1163–1168. 2011.

MERCURY ISOTHERM STUDIES FOR SELECTED BIOCHARS AND ACTIVATED CARBONS ACs 2-3 orders of magnitude stronger sorbents than natural sediments ACs stronger sorbent of Hg compared to biochars ACs and biochars equally effective for MeHg Predicted reductions in sediment with 5% AC: 94-98% for porewater Hg 73-92% for porewater MeHg Gomez-Eyles et al. ES&T 2013

BIOUPTAKE STUDIES WITH Hg CONTAMINATED SEDIMENTS Microcosm Study Design Exposure studies with freshwater oligochaetes 300 or 750 cc sediment and 200 or 500 cc of overlying water Amendments 5 % by sediment dry wt Treatments: Thiol SAMMS, GAC, MRM, HGR + Control (5 replicates) Incubated at 20~250 C, 12 h light; 12 h dark Examine contaminant concentrations in worm tissue and partitioning, and sediment geochemistry Pictures 4

Hg AND MeHg IN POREWATER AFTER AC AMENDMENT TO A RANGE OF SEDIMENTS 13.5 ng/l Freshwater river, VA Tidal Creek, NJ MD Lake Freshwater river, VA Tidal Creek, NJ MD Lake Sediment porewater Hg and MeHg both reduced after AC amendment Gilmour et al. ES&T 2013

BAFs VS. Kd FOR Hg AND MeHg, ALL TREATMENTS Tissue:sediment BAF Bioaccumulation strongly correlated with sediment Kd

PILOT TESTING: TIDAL MARSH IN NEW ENGLAND Treatments Loading (kg/plot) Hg (ng/gdw) Control FeCl2 2.3 Lime 0.5 <1 Biochar 1 SediMite (Activated C) 4.4 Sand 2” cap Clay 7 3’ X 3’ plots in two parts of the marsh set up in 3 rows of 5 plots Treatments are randomized within each row 3 replicate plots per treatment 1 day after AC application 2 years after AC application

PILOT TESTING: BERRY’S CREEK, NEW JERSEY AC amendment was performed in Fall 2012 with ongoing monitoring Coarse AC, Coarse AC with thin sand layer, Fine AC as SediMite pellets, 1-day after application Caged Leptocheirus Passive samplers for porewater PCBs Sippers for porewater Hg Native Orchestia Monitoring methods

RESEARCH MOTIVATION FOR NIEHS PROJECT There are few available remediation options for Hg contaminated sediments and soils Pilot-studies with AC amendment to sediment showed strong reductions of porewater Hg/MeHg in one site, and weak response in another (overwhelmed by redox gradient). In situ Hg remediation has been inhibited by weak understanding of MeHg production and bioavailability Need to fill key knowledge gap of the distribution and activity of Hg-methylating microorganisms in sediment The recent identification of the gene pair responsible for Hg methylation, and subsequent development of the first molecular probes provides new opportunity

SPECIFIC AIMS Specific Aim 1: Develop in situ remediation tools for Hg and MeHg impacted sediments Evaluate how black carbons impact Hg methylation and MeHg degradation rates, and microbial community structure and activity, particularly the activity of hgcA. Test the effectiveness across a broader range of biogeochemical conditions and sediment types. Identify characteristics that make sites suitable for in situ remediation, by developing a model for AC/biochar effectiveness across biogeochemical conditions. Specific Aim 2: Fill key knowledge gaps needed to develop a biogeochemical model for MeHg production and degradation in contaminated sediments and soils: Determine the role of microbial community structure in MeHg production, using genetic probes for the newly-identified microbial Hg-methylation genes. Assess the relative roles of MeHg production and degradation in net MeHg accumulation, using novel analytical methods. Determine and correlate vertical profiles of methylation and demethylation rates, with hgcAB abundance and expression in sediment cores and evaluate how different sorbent amendment strategies can influence overall MeHg bioavailability.

Planned Molecular Probe Work Samples from studies Use universal set of qualitative molecular probes (primers) spanning hgcAB Sequence products to determine Hg-methylating clades/organisms present Hg-methylating populations identified Use quantitative clade specific molecular probes for Deltaproteobacteria, Firmicutes, Archaea D F A Quantities of each hgcAB clade correlated with Hg-methylation activity in black carbon amendments, geochemical parameters (Fe, HS-; including sorbents), depth profiles of sediment cores. Determine relevant geochemical parameter influence on biological Hg-methylation activity for biogeochemical model development

ACKNOWLEDGEMENTS Steven S. Brown (The Dow Chemical Co.; Philadelphia, PA, USA) Elizabeth Henry (Anchor QEA; Saratoga Springs, NY, USA) Charles A. Menzie, Ben Amos (Exponent; Alexandria, VA, USA) Funding: NIEHS Superfund Research Program DoD SERDP/ESTCP Programs, The Dow Chemical Company, DuPont