Methylmercury (MeHg) is a highly toxic form of mercury that can bioaccumulate in fish tissue. Methylmercury is produced by anaerobic bacteria, many of which are also capable of MeHg degradation. In addition, demethylation in surface waters can occur via abiotic sunlight-mediated processes. The goal of the present study was to understand the relative importance of microbial Hg methylation/demethylation and abiotic photodemethylation that govern the mass of MeHg within an aquatic system. The study location was the Hells Canyon complex of 3 reservoirs on the Idaho–Oregon border, USA, that has fish consumption advisories as a result of elevated MeHg concentrations. Our study utilized stable isotope addition experiments to trace MeHg formation and degradation within the water column of the reservoirs to understand the relative importance of these processes on the mass of MeHg using the Water Quality Analysis Simulation Program. The results showed that rates of MeHg production and degradation within the water column were relatively low (<0.07 d^–1) but sufficient to account for most of the MeHg observed with the system. Most MeHg production within the water column appeared to occur in the spring when much of the water column was in the processes of becoming anoxic. In the surface waters, rates of photodemethylation were relatively large (up to –0.25 d^–1) but quickly decreased at depths >0.5 m below the surface. These results can be used to identify the relative importance of MeHg processes that can help guide reservoir management decisions. Environ Toxicol Chem 2021;40:1829–1839. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

中文翻译：

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美国地狱峡谷水库明暗条件下甲基汞的产生与降解

甲基汞 (MeHg) 是一种剧毒形式的汞，可在鱼类组织中生物累积。甲基汞是由厌氧细菌产生的，其中许多细菌也能够降解甲基汞。此外，地表水中的去甲基化可以通过非生物阳光介导的过程发生。本研究的目的是了解控制水生系统中甲基汞质量的微生物汞甲基化/去甲基化和非生物光去甲基化的相对重要性。研究地点是位于美国爱达荷州-俄勒冈州边界的由 3 个水库组成的地狱峡谷综合体，由于甲基汞浓度升高，该地区有鱼类消费建议。我们的研究利用稳定同位素添加实验来追踪储层水柱内甲基汞的形成和降解，以使用水质分析模拟程序了解这些过程对甲基汞质量的相对重要性。结果表明，水柱内甲基汞的产生和降解速率相对较低（<0.07 d^–1 ) 但足以解释系统中观察到的大部分甲基汞。大部分水柱内的甲基汞产生似乎发生在春季，当时大部分水柱正处于缺氧状态。在地表水中，光去甲基化的速率相对较大（高达 –0.25 d ^–1），但在地表以下 >0.5 m 的深度处迅速下降。这些结果可用于确定甲基汞过程的相对重要性，有助于指导储层管理决策。环境毒物化学2021；40:1829–1839。© 2021 SETAC。本文由美国政府雇员贡献，他们的工作在美国属于公共领域。