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Natural dissolved organic matter plays dual role in cycling of mercury


Mercury is distributed around the globe mainly through the burning of coal, industrial uses and through natural processes such as volcano eruptions. Various forms of mercury are widely found in sediments and water.

Microbes in aquatic environments transform inorganic mercury through methylation to methylmercury, a more toxic form of mercury that enters the food chain and accumulates in fish. Such biomethylation predominanantly occurs under anaerobic conditions. Interestingly, such biomethylation is not a one-way road, and other types of bacteria can transform methylmercury to less toxic forms. The environmental factors that determine the mercury availability to methylating bacteria and its transformation under these conditions remain poorly understood.

The new study:

Findings published by Oak Ridge National Laboratory's
Liyuan Liang and Baohua Gu help explain previously
reported seemingly contradictory findings.
(ORNL photo by Jason Richards)

Researchers at the Department of Energy's Oak Ridge National Laboratory have made a discovery that ultimately could help explain the complex cycling of mercury. They performed their experiments by simulating conditions found in nature.

"Until now, reactions between elemental mercury and dissolved organic matter have rarely been studied in anoxic environments," said Baohua Gu of the the lab's Environmental Sciences Division.

In a paper published January 25 in the Proceedings of the National Academy of Sciences, a team led by Gu reports that compounds from the decay of organic matter in aquatic settings affect mercury cycling. Low concentrations of these compounds can chemically reduce mercury, but as those concentrations increase, that reaction is greatly inhibited.

"This study demonstrates that in anoxic sediments and water, organic matter is not only capable of reducing mercury, but also binding to mercury," said co-author Liyuan Liang. "This binding could make mercury less available to microorganisms for making methylmercury."

The authors also noted that their paper offers a mechanism that helps explain the seemingly contradictory reports on the interaction of organic matter and mercury in nature.

Gu and Liang hope this newly gained knowledge will play a role in helping to understand how mercury cycles in aquatic and sediment environments and help in informed decision-making for mercury-impacted sites around the nation.

"Our long-term goal is to understand the mechanisms controlling the production of methylmercury in the environment, " Liang said. "This understanding could lead to ways to reduce levels of mercury in fish as this is a global problem of enormous significance."

Source: adapted from Oak Ridge National Laboratory

The original study:

 Baohua Gu, Yongrong Bian, Carrie L. Miller, Wenming Dong, Xin Jiang, and Liyuan Liang, Mercury reduction and complexation by natural organic matter in anoxic environments, Proc. Natl. Acad. Sci. USA, 108/4 (2011) 1479-1483. DOI: 10.1073/pnas.1008747108

 Related studies (newest first):

 W.M. Dong, L. Liang, S.C. Brooks, G. Southworth, B. Gu, Roles of dissolved organic matter in the speciation of mercury and methylmercury in a contaminated ecosystem in Oak Ridge, Tennessee, Environ. Chem., 7 (2010) 94–102. DOI: 10.1071/EN09091

Ariane Bouffard, Marc Amyot, Importance of elemental mercury in lake sediments, Chemosphere, 74/8 (2009) 1098-1103.DOI: 10.1016/j.chemosphere.2008.10.045

Jeffra K. Schaefer, François M.M. Morel, High methylation rates of mercury bound to cysteine by Geobacter sulfurreducens, Nature Geoscience 2 (2009) 123-126. DOI: 10.1038/ngeo412

Carrie L. Miller, George Southworth, Scott Brooks, Liyuan Liang and Baohua Gu, Kinetic Controls on the Complexation between Mercury and Dissolved Organic Matter in a Contaminated Environment, Environ. Sci. Technol., 43/22 (2009) 8548–8553. DOI: 10.1021/es901891t

Ulf Skyllberg, Competition among thiols and inorganic sulfides and polysulfides for Hg and MeHg in wetland soils and sediments under suboxic conditions: Illumination of controversies and implications for MeHg net production,  J. Geophys. Res., 113 (2008) G00C03. DOI: 10.1029/2008JG000745

Conrad Mauclair, Julie Layshock, Anthony Carpi, Quantifying the effect of humic matter on the emission of mercury from artificial soil surfaces, Appl. Geochem., 23/3 (2008) 594-601. DOI: 10.1016/j.apgeochem.2007.12.017

Carrie L. Miller, Robert P. Mason, Cynthia C. Gilmour, Andrew Heyes, Influence of dissolved organic matter on the complexation of mercury under sulfidic conditions, Environ. Toxicol. Chem., 26/4 (2007) 624–633. DOI: 10.1897/06-375R.1

E.J. Kerin, C.C. Gilmour, E. Roden, M.T. Suzuki, J.D. Coates, R.P. Mason, Mercury Methylation by Dissimilatory Iron-Reducing Bacteria, Appl. Environ. Microbiol., 72/12 (2006) 7919-7921.  DOI: 10.1128/AEM.01602-06

R.P. Mason, E.H. Kim, J. Cornwell, D. Heyes, An examination of the factors influencing the flux of mercury, methylmercury and other constituents from estuarine sediment, Mar. Chem., 102 (2006) 96–110. DOI: 10.1016/j.marchem.2005.09.021

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Tamar Barkay, Irene Wagner-Döbler, Microbial Transformations of Mercury: Potentials, Challenges, and Achievements in Controlling Mercury Toxicity in the Environment, Advances in Applied Microbiology, 57 (2005) 1-52. DOI: 10.1016/S0065-2164(05)57001-1

A.J. Poulain, M. Amyot, D. Findlay, S. Telor, T. Barkay, H. Hintelmann, Biological and photochemical production of dissolved gaseous mercury in a boreal lake, Limnol. Oceanogr.,  49 (2004) 2265–2275.

N.J. O'Driscoll, D.R.S. Lean, L.L. Loseto, R. Carignan, S.D. Siciliano, Effect of dissolved organic carbon on the photoproduction of dissolved gaseous mercury in lakes: Potential impacts of forestry, Environ. Sci. Technol., 38/9 (2004) 2664–2672. DOI: 10.1021/es034702a

J.M. Benoit, C.C. Gilmour, A. Heyes, R.P. Mason, C.L. Miller, Geochemical and biological controls over methylmercury production and degradation in aquatic ecosystems, in: Y. Cai, O.C. Braids (eds.), Biogeochem. Environ. Imp. Trace Elem. (ACS Symp. Series 835), Washington, 2003, 262–297.

J.D. Lalonde, M. Amyot, M.R. Doyon, J.C. Auclair, Photo-induced Hg(II) reduction in snow from the remote and temperate Experimental Lakes Area (Ontario, Canada), J. Geophys. Res., 108 (2003) 4200. DOI: 10.1029/2001JD001534

Markus Haitzer, George R. Aiken, Joseph N. Ryan, Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration Ratio, Environ. Sci. Technol., 36/16 (2002) 3564–3570. DOI: 10.1021/es025699i

Jeffra K. Schaefer, Jaroslaw Letowski, Tamar Barkay, mer-Mediated Resistance and Volatilization of Hg(II) Under Anaerobic Conditions,  Geomicrobiol. J., 19/1 (2002) 87—102. DOI: 10.1080/014904502317246192

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Dean Hesterberg, Jeff W. Chou, Kimberly J. Hutchison, Dale E. Sayers, Bonding of Hg(II) to Reduced Organic Sulfur in Humic Acid As Affected by S/Hg Ratio, Environ. Sci. Technol., 35/13 (2001) 2741–2745. DOI: 10.1021/es001960o

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 Related EVISA Resources

Link Database: Environmental cycling of methylmercury
Link Database: Environmental cycling of inorganic mercury
Link Database: Environmental pollution of methylmercury
Link Database: Environmental pollution of inorganic mercury

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last time modified: June 24, 2020


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