Dual Role for Organic Matter in Mercury Cycling and Toxicity


Mercury from worldwide industrialization is a widely recognized global pollutant. Concern over mercury is due to the bioaccumulation of the highly toxic methylmercury. Methylmercury is created by microbes through the conversion of inorganic mercury, Hg(II), under anaerobic conditions, such as those found in stream sediments. However, dissolved organic matter (DOM), which is ubiquitous in soils and aquatic sediments, forms strong complexes with Hg(II), influencing the microbial production of methylmercury. A research team from Oak Ridge National Laboratory (ORNL) has found that low concentrations of DOM reduce Hg(II), and that high concentrations of DOM forms complexes with Hg. The authors propose that the dual nature of DOM activity is due to the redox state of sulfur in DOM and the DOM:Hg ratio which affect the transformation of Hg and the potential microbial production of toxic methylmercury. These findings provide greater understanding of the potential transformations of Hg that are occurring not only in the mercury-contaminated East Fork Poplar Creek stream sediments on the Y-12 complex in Oak Ridge but in the sediments of many other mercury-contaminated streams worldwide.


Gu, B., Y. Bian, C. L. Miller, W. Dong, X. Jiang, and L. Liang. 2011. “Mercury Reduction and Complexation by Natural Organic Matter in Anoxic Environments,” Proceedings of the National Academy of Sciences USA. DOI:10.1073/pnas.1008747108.