SREL Reprint #3721

Mercury methylation potential and bioavailability in the sediments of two distinct aquatic systems

Chongyang Qin1,2, and Xiaoyu Xu1

1Savannah River Ecology Laboratory, University of Georgia. P O Drawer E, Aiken, SC, 29802, USA
2Jiangxi Provincial Key Laboratory of Low-Carbon Solid Waste Recycling, School of Geography and Environmental Engineering, Gannan Normal University, Ganzhou, 341000, China

Abstract: This study explored mercury (Hg) methylation potential in two distinct aquatic systems. Fourmile Creek (FMC) was historically polluted with Hg effluents from groundwater as it is a typical gaining stream, where organic matter and microorganisms in streambed are continuously winnowed. The H02 constructed wetland only receives atmospheric Hg and is rich in organic matter and microorganisms. Both systems receive Hg from atmospheric deposition now. Surface sediments were collected from FMC and H02, spiked with inorganic Hg, and cultivated in an anaerobic chamber to stimulate microbial Hg methylation reactions. Total mercury (THg) and methylmercury (MeHg) concentrations were measured at each spiking stage. Mercury methylation potential (MMP, %MeHg in THg) and Hg bioavailability were assessed with the deployment of diffusive gradients in thin films (DGTs). During the methylation process and at the same incubation stage, FMC sediment showed faster increasing rates of %MeHg and higher MeHg concentrations than H02, demonstrating a stronger MMP in the FMC sediment. Similarly, higher Hg bioavailability was observed in FMC sediment compared to the H02 as indicated by DGT-Hg concentrations. In conclusion, the H02 wetland with high levels of organic matter and microorganisms presented low MMP. But the Fourmile Creek as a gaining stream and a historical site of Hg pollution showed strong MMP and high Hg bioavailability. A related study on microbial community activities characterized the microorganisms between FMC and H02, which is attributed to be the main reason for their different methylation capabilities. Our study further brought up the considerations on remediated sites from Hg contamination: Hg bioaccumulation and biomagnification can still be elevated and higher than the surrounding environment due to lagged changes in microbial community structures. This study supported the sustainable ecological modifications of legacy Hg contamination and raised the necessity of long-term monitoring actions even after executing a remediation plan.

Keywords: Bioavailability; Diffusive gradients in thin film (DGT); Mercury; Mercury methylation potential; Methylmercury

SREL Reprint #3721

Qin, C., and X. Xu. 2023. Mercury methylation potential and bioavailability in the sediments of two distinct aquatic systems. Environmental Pollution 325: 121373.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).