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Abstract Title: Mercury methylation potential and bioavailability in the sediments of two distinct aquatic systems
Presenter Name: Xiaoyu Xu
Company/Institution: University of Georgia
Session: Mercury in Freshwater Ecosystems
Co-Authors: Xiaoyu Xu

Abstract Information :

Mercury (Hg) is a major environmental concern. The production of methyl-Hg, the major bioaccumulate Hg species, is primarily driven by microbial activities in the sediments. Thus, the study of net methylation potential (NMP) is critical to understand Hg biogeochemistry and evaluate its ecological risks. In this study, we collected sediments on the Savannah River Site (Aiken, SC, USA) from two distinct aquatic systems, the H-02 constructed wetland (no point sources; no remediation) and Fourmile Creek (historically polluted with HgCL2; then remediated). All sediment samples were spiked with inorganic Hg, cultivated in an anaerobic chamber, and tested for Hg bioavailability with the deployment of Diffusive Gradients in Thin Films (DGTs). Concentrations of total, methyl-, and bioavailable Hg were then measured and compared among sampling sites and experimental stages. The H-02 wetland (95%CI: 33.2 to 41.9 ng/g) showed higher total Hg concentrations than the Fourmile Creek (95%CI: 20.8 to 32.2 ng/g), but Fourmile Creek showed higher methyl-Hg concentrations (95%CI: 0.7 to 1.2 ng/g) and percentage of methyl-Hg (95%CI: 2.4% to 5.1%) than the H-02 wetland (95%CI of methyl-Hg: 0.5 to 0.8 ng/g; 95%CI of %methyl-Hg: 1.0% to 2.4%). Therefore, the sediment in Fourmile Creek showed stronger NMP than the H-02 wetland even the Hg contamination in Fourmile was remediated. The sediment microbial activities might contribute to the differences in NMP since high levels of Hg contamination in Fourmile modified the structure of the microbial communities. Similarly, Fourmile Creek also indicted higher Hg bioavailability than the H-02 wetland by showing higher concentrations of both DGT-indicated total (DGT-Hg) and methyl- Hg (DGT-MeHg). The observed high NMP and Hg bioavailability in Fourmile Creek demonstrated the sustainable ecological modifications of legacy Hg contamination and the necessity of long-term monitoring even after remediation considering the consistent atmospheric input of Hg to the system.

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