河口是陆地汞排放的一个重要的“汇”，研究河口汞甲基化过程对于认识区域环境中汞生物地球化学循环具有重要意义。汞细菌甲基化是水环境中甲基汞产生的主要途径。我国珠江口汞污染日趋严重，但目前对于珠江口汞甲基化细菌群落结构特征及其主要影响因素，以及两者对汞甲基化速率的影响尚缺乏基本的认识。本申请将围绕珠江口汞的细菌甲基化过程与机制这一核心问题，综合运用汞形态分析、同位素示踪及基于高通量测序的微生物群落分析等研究手段，揭示珠江口典型环境沉积物和水体中汞甲基化细菌群落的组成和时空变化规律；评价不同菌群对甲基汞原位生成的贡献；明确影响汞甲基化细菌群落的主要环境因子，探明环境因子对甲基化细菌群落、汞的甲基化速率影响机制，为合理评估珠江口区域汞污染引起的环境与健康风险提供科学依据。

Studies on mercury (Hg) methylation in the estuary, which is an important sink of terrestrial Hg, are essential to understanding of biogeochemical cycle of Hg in the regional environment. In situ bacterial methylation of inorganic Hg is the major pathway of MeHg production in the aquatic environments. The Pearl River Estuary (PRE) has been seriously polluted with Hg due to the rapid economic development and urbanization. However, there is still a lack of knowledge on characterization of bacterial community of Hg methylation and its influencing factors in the PRE, as well as their relationships with methylation rate of inorganic Hg. Therefore, this proposed project aims to provide an in-depth understanding towards bacterial methylation of inorganic Hg in the PRE. By using multiple sophisticated techniques, including Hg speciation analysis, isotope dilution, isotope tracer and high throughput DNA sequencing-based bacterial community analysis, the following specific goals will be achieved: 1) To reveal temporal-spatial distribution of Hg methylation bacterial community in the sediments and water of the PRE; 2) To estimate the contributions of dominant bacterial species to in situ production of MeHg; 3) To seek the main environmental factors related to bacterial community of Hg methylation and to elucidate the solid relationships between these factors and Hg methylation rate. The above accomplishments of this project could be especially helpful to accurate evaluation of health risk of Hg pollution in the PRE.