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Arctic Mercury Cycling May Be Linked to Ice Cover


Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times. Mercury deposition is particularly pronounced in the Arctic acting as a sink for mercury. Following deposition to surface oceans and sea ice, mercury can be converted into methylmercury, a biologically accessible form of the toxin, which biomagnifies along the marine food chain. Unfortunately, the coupling that exists between the incorporation of Hg and its biomagnification in the food chain and its geochemical cycle is not fully understood and therefore has limited the ability to explain contrasting spatiotemporal trends.

The new study:
Overall mercury levels in northern environments have been documented for some 20 years. However, the new study marks the first time that the tracking has been done using a sophisticated analysis of mercury isotopes (forms of the same atom that have different atomic masses) and an effect called "mass-independent fractionation" or MIF.

MIF is a relatively unusual change in the relative abundance of different isotopes of the same element (fractionation) that can be the result of photochemical reactions. Determining the relative amount of the MIF isotopes of mercury is considered valuable because the data can be used to trace the reactions in nature that led to the fractionation—and in turn, provide a better understanding of how the reactions work and how they impact the cycling of mercury in the environment.

Ultraviolet radiation from sunlight can fractionate mercury on the ocean surface via a process known as photodegradation. Laboratory research has shown that this reaction preferentially selects for some isotopes of mercury to move into the atmosphere while others become more abundant in the ocean. Plankton absorb the water-borne mercury, fish eat the plankton, and finally, sea birds eat the fish and pass the ingested mercury into their eggs. Therefore, the eggs are key tissues for mercury monitoring. For the current study, field groups made up of biologists and native Alaskans (for whom seabird eggs are a food source) collected eggs laid by murres, a bird species that nests year-round in three coastal regions of Alaska.

Photo: Common murres sitting on floating ice near Cape Lisburne, Alaska. Eggs from this species are being used to monitor the cycling of mercury in the Arctic biosphere.
Credit: D. Roseneau, U.S. Fish and Wildlife Service

Examination of murre eggs from the northernmost nesting areas where sea ice exists all year long revealed lower amounts of MIF mercury isotopes than in eggs collected from sites in southern Alaska where there is no ice cover. Conversely, the mercury in eggs from nests near ice-free seas reflected significantly greater effects of mass-independent fractionation. The researchers believe that ice prevents UV light from reaching the mercury, effectively suppressing photodegradation.

With the potential for global warming to dramatically reduce Arctic sea ice in the future, the relationship between ice cover and distribution of mercury in the environment is obviously an important one to investigate further. The international research team next plans to use its seabird egg isotope monitoring system to distinguish the sources of mercury contamination in coastal areas to those from oceanic waters. For this study, eggs will be collected along Alaska's Norton Sound that receives runoff from the Yukon River—including high concentrations of cinnabar, the ore from which mercury is derived—and compared to eggs from remote island colonies that are more influenced by atmospheric and oceanic mercury sources.

Teaming on this study with NIST scientists at the HML were staff from the USFWS Alaska Maritime National Wildlife Refuge (Homer, Alaska), Environment Canada (Saskatoon, Saskatchewan, Canada), the Labotatoire des Mécanismes et Transferts en Géologie (Toulouse, France) and the Institut Pluridisciplinaire de Recherche sur l'Environnement et les Materiaux (Pau, France). Financial support for the research was provided by NIST, the French Centre National de la Recherche Scientifique and a grant from the French Agence Nationale de Recherche.

The HML is a unique partnership of governmental and academic agencies including NIST, NOAA's National Ocean Service, the South Carolina Department of Natural Resources, the College of Charleston and the Medical University of South Carolina.

Source: Adapted from NIST

The original study

  D. Point, J.E. Sonke, R.D. Day, D.G. Roseneau, K.A. Hobson, S.S. Vander Pol, A.J. Moors, R.S. Pugh, Olivier F.X. Donard and P.R. Becker, Methylmercury photodegradation influenced by sea ice over in Arctic marine ecosystems, Nature Geoscience. Published online Jan. 16, 2011. doi:10.1038/ngeo1049

Related studies

Laura S. Sherman, Joel D. Blum, Kelsey P. Johnson, Gerald J. Keeler, James A. Barres, Thomas A. Douglas, Mass-independent fractionation of mercury isotopes in Arctic snow driven by sunlight, Nature Geoscience 3 (2010) 173-177. doi:10.1038/ngeo758

Laure Laffont, Jeroen E. Sonke, Laurence Maurice, Holger Hintelmann, Marc Pouilly, Yuba Snchez Bacarreza, Tamar Perez, Philippe Behra, Anomalous Mercury Isotopic Compositions of Fish and Human Hair in the Bolivian Amazon, Environ. Sci. Technol., 2009, 43 (23), pp 8985–8990. DOI: 10.1021/es9019518.

R. Das, V.J.M. Salters, A.L. Odom, A case for in vivo mass-independent fractionation of mercury isotopes in fish, Geochem. Geophys. Geosyst., 10 (2009) Q11012. doi: 10.1029/2009GC002617

Pablo Rodríguez-González, Vladimir N. Epov, Romain Bridou, Emmanuel Tessier, Remy Guyoneaud, Mathilde Monperrus, David Amouroux, Species-Specific Stable Isotope Fractionation of Mercury during Hg(II) Methylation by an Anaerobic Bacteria (Desulfobulbus propionicus) under Dark Conditions, Environ. Sci. Technol., 43/24 (2009) 9183–9188. DOI: 10.1021/es902206j

Sanghamitra Ghosh, Yingfeng Xu, Munir Humayun, and Leroy Odom, Mass-independent fractionation of mercury isotopes in the environment, Geochem. Geophys. Geosyst., 9/3 (2008) Q03004.  doi:10.1029/2007GC001827

T.A. Jackson, D.M. Whittle, M.S. Evans, D.C.G. Muir, Evidence for mass-independent and mass-dependent fractionation of the stable isotopes of mercury by natural processes in aquatic ecosystems, Appl. Geochem. 23 (2008) 547–571. doi:10.1016/j.apgeochem.2007.12.013

Steve Lindberg, Russell Bullock, Ralf Ebinghaus, Daniel Engstrom, Xinbin Feng, William Fitzgerald, Nicola Pirrone, Eric Prestbo, and Christian Seigneur, A Synthesis of Progress and Uncertainties in Attributing the Sources of Mercury in Deposition, AMBIO,36/1 (2007)19-33. doi: 10.1579/0044-7447(2007)36[19:ASOPAU]2.0.CO;2

Rusty D. Day, Stacy S. Vander Pol, Steven J. Christopher, W. Clay Davis, Rebecca S. Pugh, Kristin S. Simac, David G. Roseneau, Paul R. Becker, Murre Eggs (Uria aalge and Uria lomvia) as Indicators of Mercury Contamination in the Alaskan Marine Environment, Environ. Sci. Technol., 40/3 (2006) 659–665. DOI: 10.1021/es051064i

B.M. Braune, G.M. Donaldson, K.A. Hobson, Contaminant residues in seabird eggs from the Canadian Arctic. Part I. Temporal trends 1975–1998, Environmental Pollution, 114/1 (2001) 39-54. doi:10.1016/S0269-7491(00)00210-4 |

Related EVISA Resources

Link Database: Mercury cycling in the Environment
Link Database: Mercury environmental pollution

Related EVISA News (newest first)

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August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide
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February 11, 2009: Mercury in Fish is a Global Health Concern
October 30, 2008: Precautionary approach to methylmercury needed
May 3, 2007: More nutritious food helps reduce methylmercury in the aquatic food chain
March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning 
February 18, 2007: New research results suggest that mercury hotspots in the northeastern US are home made
October 9, 2006: Linking atmospheric mercury to methylmercury in fish
September 23, 2006: Report Finds Mercury Contamination Permeates Wildlife Systems
August 16, 2006: Mercury pollution threatens health worldwide, scientists say
June 16, 2006: Sulfur fuels the methylation of mercury
February 17, 2006: Study shows link between clear lakes and methylmercury contamination in fish
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last time modified: January 21, 2011


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