| Summary: | 碩士 === 國立中央大學 === 環境工程研究所在職專班 === 107 === Recent studies have shown that in addition to marine foods, rice consumption is another significant route of human exposure to methylmercury. However, knowledge of the mechanism that underpins mercury methylation in rice paddies as well as the uptake and accumulation of methylated mercury in rice plants is still limited. To explore this subject, we began with field studies that measured relevant geochemical and microbial parameters pertaining to mercury cycling in a suite of rice paddies proximate to the Taichung coal-fired power station in 2014; soil incubations with synthetic growth media were also carried out. It was observed that sulfate-reducing bacteria (SRB) were likely the primary mercury methylators under the investigational conditions. However, because these tests did not directly use the pore water from the rice fields, nor did them analyze the detailed structure of the microbial population, the obtained results might not be able to thoroughly reflect the actual picture of mercury biogeochemical transformations in the paddy systems. Therefore, in this study we modified our previous set-ups by using not only the rhizosphere soil but also the porewater of our study sites to probe the potential of in situ mercury methylation that is closer to the reality. Additionally, quantitative real-time PCR (i.e., qPCR) was incorporated into the investigation to obtain the information of microbial activity at the molecular level in terms of gene copy numbers. Results show that the methylmercury degradation rates under different experimental conditions were similar, indicating that the degree of methylmercury accumulation in paddy fields might depend mainly on the methylation intensity. The combined results of chemical analysis and qPCR showed that the principal mercury methylating guild of the selected paddy fields might still be Deltaproteobacteria, in particular SRB. The outcome of this study may serve as a reference for the prevention and management strategies of mercury methylation in arable land systems.
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