DEVELOPMENT OF IN-SITU MERCURY REMEDIATION APPROACHES BASED ON

METHYLMERCURY BIOAVAILABILITYUpal Ghosh and James Sanders,

Department of Chemical, Biochemical, and Environmental Engineering, UMBC

Cynthia GilmourSmithsonian Environmental Research Center

Dwayne EliasUniversity of Tennessee/ Oak Ridge National Laboratory

Clu-In webinar: Biogeochemical Factors Impacting in situ Remediation

Metals and PAH mixturesFeb 2, 2015

2

Activated carbon amended to surficial sediments reduces uptake of bioaccumulative pollutants in the food chain through:

1)Reduced porewater concentrations2)Reduced bioaccumulation in benthic organisms 3)Reduced flux into water column and uptake in the pelagic food web.

RESEARCH BACKGROUND

See Feature Article : In-situ sorbent amendments: A new direction in contaminated sediment management. Ghosh et al. Environ. Sci. Technol. 45, 1163–1168. 2011.

Demonstrated for PCBs in several pilot studies

Q: Can AC or biochar sequester Hg/MeHg and reduce bioavailability?

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

AC

bioc

har

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

BIOUPTAKE STUDIES WITH Hg CONTAMINATED SEDIMENTS

Hg AND MeHg IN POREWATER AFTER AC AMENDMENT TO A RANGE OF SEDIMENTS

13.5 ng/l

Sediment porewater Hg and MeHg both reduced after AC amendment

Freshwater river, VA

Tidal Creek, NJ

Tidal Creek, MD

FreshwaterLake

Freshwater river, VA

Tidal Creek, NJ

Tidal Creek, MD

FreshwaterLake

Gilmour et al. ES&T 2013

Sediment:porewater KD

102 103 104 105 106 107 108

BA

F

0.01

0.1

1

10

100

Inorganic HgMeHg

BAFs VS. Kd FOR Hg AND MeHg, ALL TREATMENTS

Bioaccumulation strongly correlated with sediment Kd

Tiss

ue:s

edim

ent B

AF

• 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

Treatments Loading (kg/plot)

Hg (ng/gdw)

Control

FeCl2 2.3

Lime 0.5 <1

Biochar 1 <1

SediMite (Activated C)

2.3 4.4

Sand 2” cap <1

Clay 2” cap 7

PILOT TESTING: TIDAL MARSH IN NEW ENGLAND

1 day after AC application 2 years after AC application

AC amendment was performed in Fall 2012 with ongoing monitoring

Coarse AC, Coarse AC with thin sand layer, Fine AC as SediMite pellets,

PILOT TESTING: BERRY’S CREEK, NEW JERSEY

1-day after application

Native OrchestiaCaged

LeptocheirusPassive samplers for porewater PCBs

Sippers for porewater Hg

Mon

itorin

g m

etho

ds

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 AIMSSpecific 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.

Use universal set of qualitative molecular probes (primers) spanning hgcAB

Use quantitative clade specific molecular probes for Deltaproteobacteria, Firmicutes, Archaea

Sequence products to determine Hg-methylating clades/organisms present

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.

Samples from studies

Hg-methylating populations identified

D F A

Determine relevant geochemical parameter influence on biological Hg-methylation activity for biogeochemical model development

Planned Molecular Probe Work

ACKNOWLEDGEMENTS

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Funding:

NIEHS Superfund Research Program

DoD SERDP/ESTCP Programs, The Dow Chemical Company, DuPont

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)