1. 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

2. 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–

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. 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.

11. 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

12. 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