Department of Environmental Science, Stockholm University, 106 91 Stockholm, Sweden.
Environ Sci Technol. 2022 May 3;56(9):5920-5928. doi: 10.1021/acs.est.1c08443. Epub 2022 Apr 20.
Photochemical demethylation of dimethylmercury (DMHg) could potentially be an important source of monomethylmercury (MMHg) in sunlit water. Whether or not DMHg is photochemically degraded when dissolved in water is, however, debated. While an early study suggested DMHg dissolved in natural waters to readily degrade, later work claimed DMHg to be stable in seawater under natural sunlight and that early observations may be due to experimental artifacts. Here, we present experimental data showing that DMHg is readily degraded by photochemical processes in different natural waters (including water from a DOC-rich stream, the Baltic Sea, and the Arctic Ocean) as well as in artificial seawater and purified water. For most of the waters, the degradation rate constant () for DMHg measured in indoor experiments exceeded, or was close to, the observed for MMHg. Outdoor incubations of DMHg in purified water and Arctic Ocean surface water further confirmed that DMHg is photochemically degraded under natural sunlight. Our study shows that DMHg is photochemically degraded in a range of natural waters and that this process may be a source of MMHg in sunlit waters where the supply or formation of DMHg is sufficient.
光解二甲基汞（DMHg）可能是阳光照射下水体中单甲基汞（MMHg）的一个重要来源。然而，DMHg 溶解在水中是否会发生光化学降解仍存在争议。尽管早期的一项研究表明，DMHg 溶解在天然水中容易降解，但后来的研究声称 DMHg 在自然阳光照射下的海水中稳定存在，早期的观察结果可能是由于实验误差。在这里，我们提供了实验数据，表明 DMHg 很容易通过不同天然水（包括富含 DOC 的溪流、波罗的海和北冰洋的水）以及人工海水和纯净水的光化学过程降解。对于大多数水，在室内实验中测量的 DMHg 降解速率常数（）超过，或接近，观察到的 MMHg。在纯化水和北冰洋地表水的 DMHg 户外培养进一步证实了 DMHg 在自然光下发生光化学降解。我们的研究表明，DMHg 在一系列天然水中发生光化学降解，在 DMHg 供应或形成充足的阳光照射水域中，这一过程可能是 MMHg 的来源。
