Molecular composition of organic matter controls methylmercury formation in boreal lakes.

Bravo AG, Bouchet S, Tolu J, Björn E, Mateos-Rivera A, Bertilsson S

Nat Commun 8 (-) 14255 [2017-02-09; online 2017-02-09]

A detailed understanding of the formation of the potent neurotoxic methylmercury is needed to explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercury methylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments.

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PubMed 28181492

DOI 10.1038/ncomms14255

Crossref 10.1038/ncomms14255

ncomms14255

pmc PMC5309796