Researchers at the Department of Energy’s Oak Ridge National Laboratory have made a discovery that ultimately could help explain the contradictory findings for the behaviour of mercury in the aquatic environment.
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 Environmen
t, 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
U. Skyllberg, P.R. Bloom, J. Qian, C.M. Lin, W.F. Bleam, Complexation of mercury(II) in soil organic matter: EXAFS evidence for linear two-coordination with reduced sulfur groups
, Environ. Sci. Technol., 40 (2006) 4174–4180. doi: 10.1021/es0600577
H.A. Wiatrowski, P.M. Ward, T. Barkay, Novel reduction of mercury (II) by mercury-sensitive dissimilatory metal reducing bacteria
, Environ. Sci. Technol., 40 (2006) 6690–6696. doi: 10.1021/es061046g
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
G.R. Golding, Carol A. Kelly, Richard Sparling, Peter C. Loewen, John W. M. Rudd, Tamar Barkay, Evidence for facilitated uptake of Hg(II) by Vibrio anguillarum and Escherichia coli under anaerobic and aerobic conditions
, Limnol. Oceanogr., 47 (2002) 967–975. DOI: 10.4319/lo.2002.47.4.0967
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
Kristofer R. Rolfhus, William F. Fitzgerald, The evasion and spatial/temporal distribution of mercury species in Long Island Sound, CT-NY
, Geochim. Cosmochim. Acta, 65/3 (2001) 407-418. doi:10.1016/S0016-7037(00)00519-6
Julio Cesar Rocha, Ézio Sargentini Junior, Luiz Fabricio Zara, André Henrique Rosa, Ademir dos Santos, Peter Burba, Reduction of mercury(II) by tropical river humic substances (Rio Negro) — A possible process of the mercury cycle in Brazil
, Talanta, 53/3 (2000) 551-559. doi:10.1016/S0039-9140(00)00532-4
H. Hintelmann, K. Keppel-Jones, R.D. Evans, Constants of mercury methylation and demethylation rates in sediments and comparison of tracer and ambient mercury availability
, Environ. Toxicol. Chem., 19 (2000) 2204–2211. doi: 10.102/ETC.5620190909
K. Xia, U.L. Skyllberg, W.F. Bleam, P.R. Bloom, E.A. Nater, P.A. Helmke, X-ray absorption spectroscopic evidence for the complexation of Hg(II) by reduced sulfur in soil humic substances
, Environ. Sci. Technol., 33 (1999) 257–261. DOI: 10.1021/es980433q
M. Costa, P.S. Liss, Photoreduction of mercury in sea water and its possible implications for Hg0 air–sea fluxes
, Mar. Chem., 68/1-2 (1999) 87-95. doi:10.1016/S0304-4203(99)00067-5
F.M.M. Morel, A.M.L. Kraepiel, N. Amyot, The chemical cycle and bioaccumulation of mercury
, Annu. Rev. Ecol. Syst., 29 (1998) 543–566. doi: 10.1146.annurev.ecolsys.29.1.543
Marl Amyot, Greg Mierle, David Lean, Donald J. Mc Queen, Effect of solar radiation on the formation of dissolved gaseous mercury in temperate lakes
, Geochim. Cosmochim. Acta, 61/5 (1997) 975-987. doi:10.1016/S0016-7037(96)00390-0
T. Barkay, M. Gillman, R.R. Turner, Effects of dissolved organic carbon and salinity on bioavailability of mercury
, Appl. Environ. Microbiol., 63/11 (1997) 4267-4271.
Z. F. Xiao, D. Strömberg and O. Lindqvist, Influence of humic substances on photolysis of divalent mercury in aqueous solution
, Water, Air, soil Pollut., 80/1-4 (1995) 789-798. DOI: 10.1007/BF01189730
B.M. Miskimmin, J.W.M. Rudd, C.A. Kelly, Influence of dissolved organic-carbon, pH, and microbial respiration rates on mercury methylation and demethylation in lake water
, Can. J. Fish. Aquat. Sci., 49 (1992) 17–22.
C.C. Gilmour, E.A. Henry, R. Mitchell, Sulfate stimulation of mercury methylation in fresh-water sediments
, Environ. Sci. Technol., 26 (1992) 2281–2287. doi: 10.1021/es00035a029
E. Schuster, The behavior of mercury in the soil with special emphasis on complexation and adsorption processes—a review of the literature
, Water Air Soil Pollut., 56 (1991) 667–680. DOI: 10.1007/BF00342308
B. Allard, I. Arsenie, Abiotic reduction of mercury by humic substances in aquatic system—an important process for the mercury cycle
, Water Air Soil Pollut., 56 (1991) 457–464. doi: 10.1007/BF00342291
T. Barkay, C. Liebert. M. Gillman, Environmental significance of the potential for mer(Tn21)-mediated reduction of Hg2+ to Hg0 in natural waters
, Appl. Environ. Microbiol., 55 (1989) 1196–1202.
G.C. Compeau, R. Bartha, Sulfate-Reducing Bacteria: Principal Methylators of Mercury in Anoxic Estuarine Sediment
, Appl Environ Microbiol., 50/2 (1985) 498-502.
Sheng C. Fang, Studies on the sorption of elemental mercury vapor by soils
, Arch. Environm. Contain. Toxicol., 10 (1981) 193-201. doi: 10.1007/BF01055621
James J. Alberts, James E. Schindler, Richard W. Miller, Dale E. Nutter, Elemental Mercury Evolution Mediated by Humic Acid
, Science, 184/4139 (1974) 895-897. DOI: 10.1126/science.184.4139.895 Related EVISA Resources EVISA Link Database: Mercury cycling in the Environment EVISA Link Database: Mercury environmental pollution Related News EVISA News, January 21, 2011: Arctic Mercury Cycling May Be Linked to Ice Cover EVISA News, August 18, 2010: Methylmercury: What have we learned from Minamata Bay? EVISA News, June 28, 2010: New Study Examines Why Mercury is More Dangerous in Oceans EVISA News, September 8, 2009: Inorganic Mercury Level in US Women increases EVISA News, August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide EVISA News, June 17, 2009: 'Surprisingly High Levels' of Methylmercury Contamination found in Groundwater EVISA News, May 3, 2009: Ocean mercury on the rise EVISA News, February 11, 2009: Mercury in Fish is a Global Health Concern EVISA News, October 30, 2008: Precautionary approach to methylmercury needed EVISA News, May 3, 2007: More nutritious food helps reduce methylmercury in the aquatic food chain EVISA News, March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning EVISA News, February 18, 2007: New research results suggest that mercury hotspots in the northeastern US are home made EVISA News, October 9, 2006: Linking atmospheric mercury to methylmercury in fish EVISA News, September 23, 2006: Report Finds Mercury Contamination Permeates Wildlife Systems EVISA News, August 16, 2006: Mercury pollution threatens health worldwide, scientists say EVISA News, June 16, 2006: Sulfur fuels the methylation of mercury EVISA News, February 17, 2006: Study shows link between clear lakes and methylmercury contamination in fish EVISA News, February 9, 2006: Study show high levels of mercury in women related to fish consumption
last time modified: February 15, 2011