黄渤海甲基汞来源与归趋、关键迁移转化过程及机理研究

Coastal ocean plays an important role in the global cycling of mercury (Hg). It could be an important sink or a natural source of Hg, as well as a critical source of methylmercury (MeHg). Elevated Hg has been detected in seafood from Bohai Sea and Yellow Sea, suggesting that Hg pollution has posed great risk to the health of both humans and wildlife nearby or in these two ecosystems. Among all Hg species present in aquatic environments, MeHg has been a focus of attention due to its high toxicity and accumulation through food chains. However, most previous efforts have been made to investigate the cycling of inorganic mercury, rather than MeHg, in the Bohai Sea and Yellow Sea. There is still a lack of knowledge on the distribution of MeHg in different matrices, the sources and sinks of MeHg, and the controlling processes in these two systems. Focused on this research gap, this project is aimed to provide an in-depth understanding towards the cycling of MeHg in the Bohai Sea and Yellow Sea. By using various techniques, including isotope dilution, isotope tracer, and field investigation, the following three specific goals will be accomplished: 1) Quantify the contributions of river loading, wet deposition, in-situ production and degradation, input of MeHg from sediment to water body and MeHg exchange between the target system and boundary systems to MeHg in the Bohai Sea and Yellow Sea; 2) Identify the major sources and sinks of MeHg in the Bohai Sea and Yellow Sea; 3) Assess the importance of Hg methylation/demethylation in MeHg cycling and the mechanisms of Hg methylation/demethylation in sediments and waters. The accomplishment of this project is expected to provide a better understanding of Hg pollution in the Bohai Sea and Yellow Sea. Such studies are also necessary for predicting the long-term impact of Hg pollution and making effective measures to minimize the risk of Hg contamination in these two ecosystems.

近海是汞的一个重要的“汇”和“二次源”以及甲基汞的一个重要的“源”，在全球汞循环中起着重要作用。我国黄渤海水产品中存在着汞超标现象，威胁到周边居民的健康和海洋生态环境健康。目前黄渤海海域汞污染的研究主要集中于总汞方面，而对于水环境中毒性最强、更易通过食物链富集的甲基汞研究较少，对于甲基汞在该区域环境介质中的分布、主要来源、归趋、控制过程和机理等尚缺乏最基本的认识。本课题拟针对黄渤海甲基汞污染这一核心问题，综合运用现场调查及同位素示踪等手段，定量估算陆源河流输入、大气沉降、原位生成和降解、沉积物释放和外海交换对黄海和渤海甲基汞的贡献，弄清黄渤海甲基汞的主要来源和去除途径，明确几个关键迁移转化过程（水层甲基化/去甲基化过程、沉积物甲基化/去甲基化过程）在黄渤海汞循环中的作用及过程机理，研究将为合理评价该海域汞污染现状、预测汞污染的可能长期影响及采取有效应对措施提供科学依据。

近海是汞的一个重要的“汇”和“二次源”以及甲基汞的一个重要的“源”，在全球汞循环中起着重要作用。我国黄渤海水产品中存在着汞超标现象，威胁到周边居民的健康和海洋生态环境健康。目前黄渤海海域汞污染的研究主要集中于总汞方面，而对于水环境中毒性最强、更易通过食物链富集的甲基汞研究较少，对于甲基汞在该区域环境介质中的分布、主要来源、归趋、控制过程和机理等尚缺乏最基本的认识。本课题针对黄渤海甲基汞污染这一核心问题，综合运用现场调查、同位素稀释和示踪、全过程通量估算等技术，研究了黄渤海总汞、甲基汞和溶解气态汞污染状况及其影响因素，识别了甲基汞的关键“源”和“汇”，评估了汞甲基化/去甲基化过程在甲基汞循环中的作用并探究了其过程机制。取得主要成果包括：1）发现黄渤海水体和沉积物总汞浓度较高但甲基汞所占比例较低的现象，并推断这可能是相对高汞排放强度中国近海生物体内汞含量相对较低的主要原因之一；2）研究发现中国近海甲基汞占比较低的主要原因包括：沉积物富集水体中无机汞能力较弱、沉积物净甲基化速率和向水体释放甲基汞速率较慢、水体降解较快等；3）全过程定量估算结果表明沉积物净甲基化过程（生物）是黄渤海甲基汞最主要的“源”，而水层去甲基化过程（光化学+生物）是甲基汞的关键“汇”； 4）UV-A 和UV-B为主要引起汞光致甲基化和去甲基化的光波段，硫酸盐还原菌和产甲烷菌分别是黄渤海沉积物和水体中汞生物甲基化和去甲基化过程的关键微生物。本课题研究增进了对黄渤海甲基汞来源和归趋的了解，有望为预测和有效控制该海域的汞风险提供科学依据。