Date of Award
5-1-2024
Degree Name
Master of Science
Department
Civil Engineering
First Advisor
Fakhraei, Habibollah
Abstract
Inorganic mercury (Hg) is converted to potential neurotoxic methylmercury (MeHg) by a natural process called Hg methylation. MeHg can be biomagnified in the food chain, thus the consumption of Hg-contaminated fish contributes to harmful human health issues. Selenium (Se) inhibits the Hg bioavailability to the methylating bacteria by forming mercuric selenide (HgSe). Pseudodesulfovibrio mercurii, a type of sulfate-reducing bacteria (SRB) cultures were grown in anaerobic environments using an estuarine sulfate lactate growth medium to evaluate the effects of Hg concentrations, bacterial growth phase, and sodium selenate in the Hg methylation process. Bacterial cultures contained two types of mercuric (II) nitrate, dissolved and nanoparticles with 1 nM, 2 nM, and 3 nM concentrations in anoxic conditions. In a different experimental batch, various concentrations of sodium selenate (VI) were added to the Hg-contained medium to evaluate the effect of Se in the Hg methylation process. Dissolved Hg produced higher net MeHg than nanoparticulate Hg throughout the incubation period in the culture medium. Bacterial culture medium stressed with high-level Hg concentrations showed increased MeHg production (pM) but decreased Hg methylation rate (%) for the dissolved Hg. During the methylation process in the presence of Se, net MeHg production was reduced significantly compared to the culture medium solely exposed to Hg. The significant reduction of MeHg generation suggests an interference in the Hg methylation process due to the presence of 50-, 75-, and 100-fold higher Se than Hg. This study reassures the antagonistic effect between Hg and Se at the molecular level. Moreover, this study represents a novel approach when the antagonistic effect of nanoparticulate Hg and selenate is observed at the bacterial level. These interactions between Hg and Se are crucial for a better understanding of the Hg methylation process. This research will help to provide a solid foundation for a better understanding of MeHg generation in anaerobic aquatic conditions.
Access
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