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Methylation of inorganic mercury in polar marine waters

Nature Geoscience volume 4, pages 298–302 (2011)Cite this article

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Abstract

Monomethylmercury is a neurotoxin that accumulates in marine organisms, with serious implications for human health1. The toxin is of particular concern to northern Inuit peoples, for example, whose traditional diets are composed primarily of marine mammals and fish2. The ultimate source of monomethylmercury to marine organisms has remained uncertain, although various potential sources have been proposed, including export from coastal 3 and deep-sea4 sediments and major river systems5,6, atmospheric deposition7 and water-column production8,9. Here, we report results from incubation experiments in which we added isotopically labelled inorganic mercury and monomethylmercury to seawater samples collected from a range of sites in the Canadian Arctic Archipelago. Monomethylmercury formed from the methylation of inorganic mercury in all samples. Demethylation of monomethylmercury was also observed in water from all sites. We determined steady-state concentrations of monomethylmercury in marine waters by incorporating the rate constants for monomethylmercury formation and degradation derived from these experiments into a numerical model. We estimate that the conversion of inorganic mercury to monomethylmercury in the water column accounts for around 47% (±62%, standard deviation) of the monomethylmercury present in polar marine waters, with site-to-site differences in inorganic mercury and monomethylmercury levels accounting for most of the variability. We suggest that water-column methylation of inorganic mercury is a significant source of monomethylmercury in pelagic marine food webs in the Arctic, and possibly in the world’s oceans in general.

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Figure 1: Conceptual model of Hg methylation/demethylation in marine waters.
Figure 2: Production of MMHg in marine waters.
Figure 3: Demethylation of MMHg in marine waters.

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Acknowledgements

Financial support for this study was provided by ArcticNet, and the Northern Scientific Training Program of the Department of Indian and Northern Affairs Canada. I.L. was financially supported by a NSERC Graduate Scholarship and an Alberta Ingenuity Studentship. We are grateful to B. Danielson, J. Carrie and the crew of the CCGS Amundsen for assistance collecting samples, Y. Gratton and his team for providing conductivity–temperature–depth data and J-E. Tremblay and his team for providing chlorophyll and nutrient data, as well as M. Lewis and A. Potapov for their help with data analysis and Q. Wang for calculating ocean-current velocities. We would also like to thank S. Berkel and B. Dimock for laboratory help, and C. Nielsen for producing Supplementary Fig. S1.

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  1. Jane L. Kirk

    Present address: Present address: Canada Centre for Inland Waters, Environment Canada, Burlington, Ontario, L7R 4A6, Canada,

Authors and Affiliations

  1. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada

    Igor Lehnherr, Vincent L. St. Louis & Jane L. Kirk

  2. Department of Chemistry, Trent University, Peterborough, Ontario, K9J 7B8, Canada

    Holger Hintelmann

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Contributions

V.L.St.L. initiated the study; I.L., H.H. and V.L.St.L. designed experiments and I.L. and J.L.K. carried them out; I.L. carried out data analysis and wrote the manuscript. All authors commented on the manuscript and contributed to discussions of results.

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Correspondence to Igor Lehnherr or Jane L. Kirk.

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The authors declare no competing financial interests.

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Lehnherr, I., St. Louis, V., Hintelmann, H. et al. Methylation of inorganic mercury in polar marine waters. Nature Geosci 4, 298–302 (2011). https://doi.org/10.1038/ngeo1134

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