Dissolved organic matter thiol concentrations determine methylmercury bioavailability across the terrestrial-marine aquatic continuum

Emily Seelen (), Liem-Nguyen Van, Urban Wünsch, Zofia Baumann, Robert Mason, Ulf Skyllberg and Erik Björn ()
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Emily Seelen: University of Connecticut, Department of Marine Sciences
Liem-Nguyen Van: Umeå University, Department of Chemistry
Urban Wünsch: National Institute of Aquatic Resources, Section for Oceans and Arctic
Zofia Baumann: University of Connecticut, Department of Marine Sciences
Robert Mason: University of Connecticut, Department of Marine Sciences
Ulf Skyllberg: Swedish University of Agricultural Sciences, Department of Forest Ecology and Management Umeå
Erik Björn: Umeå University, Department of Chemistry

Nature Communications, 2023, vol. 14, issue 1, 1-13

Abstract: Abstract The most critical step for methylmercury (MeHg) bioaccumulation in aquatic food webs is phytoplankton uptake of dissolved MeHg. Dissolved organic matter (DOM) has been known to influence MeHg uptake, but the mechanisms have remained unclear. Here we show that the concentration of DOM-associated thiol functional groups (DOM-RSH) varies substantially across contrasting aquatic systems and dictates MeHg speciation and bioavailability to phytoplankton. Across our 20 study sites, DOM-RSH concentrations decrease 40-fold from terrestrial to marine environments whereas dissolved organic carbon (DOC), the typical proxy for MeHg binding sites in DOM, only has a 5-fold decrease. MeHg accumulation into phytoplankton is shown to be directly linked to the concentration of specific MeHg binding sites (DOM-RSH), rather than DOC. Therefore, MeHg bioavailability increases systematically across the terrestrial-marine aquatic continuum as the DOM-RSH concentration decreases. Our results strongly suggest that measuring DOM-RSH concentrations will improve empirical models in phytoplankton uptake studies and will form a refined basis for modeling MeHg incorporation in aquatic food webs under various environmental conditions.

Date: 2023
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DOI: 10.1038/s41467-023-42463-4

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