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Abstract Title: Utility of Diffusive Gradient in Thin-film Passive Samplers for Quantifying Hg Bioavailability for Methylation and Biomagnification
Presenter Name: Natalia Neal-Walthall
Company/Institution: Duke University
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling
Day and Session: Friday 29th July - Session Two
Start Time: 09:30 UTC
Co-Authors: Heileen Hsu-Kim

Abstract Information :

The risk of mercury pollution in aquatic ecosystems depends on the bioavailability of inorganic Hg forms for methylating microorganisms and the biomagnification potential of methylmercury (MeHg) in the food web. This risk is difficult to manage because of the complexity of biogeochemical processes for mercury and the need for accessible techniques to navigate this complexity. Here, we studied diffusive gradient in thin-film (DGT) passive samplers for enabling simultaneous quantification of inorganic Hg (IHg) methylation potential and MeHg bioaccumulation potential of MeHg in freshwater wetlands. We performed experiments with three outdoor freshwater wetland mesocosms that were amended with four isotopically-labelled and geochemically relevant IHg forms that represent a range of methylation potentials. For a three month period, we quantified the distribution of IHg and MeHg from each isotope spike in surface water, sediment, periphyton and macrofauna tissues, as well as uptake flux of mercury in DGTs placed in water and sediment of the wetlands. Sediment and surface water concentrations of MeHg generally correlated with IHg-DGT uptake flux, suggesting that DGT samplers are accessing IHg forms that are bioavailable to methylating microorganisms. We also observed correlations between total Hg-DGT uptake flux and MeHg levels in periphyton biofilms, submergent plant stems, snails and mosquitofish in the ecosystem. These correlations were better for DGTs deployed in the water column compared to DGTs in the sediments, suggesting the importance of vertical distribution of bioavailable MeHg in relation to food sources for macrofauna. We developed biodynamic equations that utilize MeHg-DGT uptake flux data to parameterize a model for MeHg bioaccumulation rate in the mesocosm ecosystems. Overall, these results demonstrate that DGT passive samplers could be a relatively efficient tool for predicting IHg methylation and MeHg bioaccumulation potentials. Such tools can help discretize the geochemical and biological processes that contribute to MeHg bioaccumulation in the aquatic environment.

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