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Abstract Title: Dissolved Organic Matter Thiol Concentrations Determine Methylmercury Bioavailability Across the Terrestrial-Marine Aquatic Continuum
Presenter Name: Emily Seelen
Company/Institution: University of Southern California
Session: Mercury in Marine Ecosystems
Day and Session: Thursday 28th July - Session Three
Start Time: 12:00 UTC
Co-Authors: Emily Seelen

Abstract Information :

The most critical step for methylmercury (MeHg) bioaccumulation in aquatic food webs is phytoplankton uptake of dissolved MeHg. Dissolved organic matter (DOM) is known to influence MeHg uptake, but the mechanisms remained unclear. We show that the concentration of DOM-associated thiol functional groups (DOM-RSH) dictates MeHg speciation and bioavailability across terrestrial and marine aquatic systems. Specifically, DOM-RSH concentrations decreased 40-fold from terrestrial to marine environments whereas dissolved organic carbon, the typical proxy for MeHg binding sites, only had a 5-fold decrease. Quantifying the specific MeHg binding sites (DOM-RSH) enabled accurate prediction of MeHg accumulation in phytoplankton via the inverse relationship: MeHg volume concentration factor ? 1/[DOM-RSH]. MeHg bioavailability thereby decreased systematically across the terrestrial-marine aquatic continuum. Based on the identified molecular principles for MeHg interactions with DOM we formulated a generalizable MeHg bioavailability model to predict MeHg incorporation in aquatic food webs under various environmental conditions.

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