Photo-induced degradation of dimethylmercury (DMHg) is considered to be an important source for the generation of methylmercury (MMHg). However, studies on DMHg photodegradation are scarce, and it is even debatable about whether DMHg can be degraded in natural waters. Herein, we found that both DMHg and MMHg could be photodegraded in three natural waters collected from the Yellow River Delta, while in pure water only DMHg photodegradation occurred under visible light irradiation. The effects of different environmental factors on DMHg photodegradation were investigated, and the underlying mechanisms were elucidated by density functional theory calculations and a series of control experiments. Our findings revealed that the DMHg degradation rate was higher in the tidal creek water compared to Yellow River, Yan Lake, and purified water. NO, NO, and DOM could promote the photodegradation with DOM and NO showing particularly strong positive effects. Different light sources were employed, and UV light was found to be more effective in DMHg photodegradation. Moreover, MMHg was detected during the photodegradation of DMHg, confirming that the photochemical demethylation of DMHg is a source of MMHg in sunlit water. This work may provide a novel mechanistic insight into the DMHg photodegradation in natural waters and enrich the study of the global biogeochemical cycle of Hg.

中文翻译：

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二甲基汞在不同天然水中的光诱导降解

二甲基汞（DMHg）的光诱导降解被认为是甲基汞（MMHg）产生的重要来源。然而，关于DMHg光降解的研究还很少，甚至对于DMHg能否在自然水中降解还存在争议。在此，我们发现在黄河三角洲收集的三种天然水中，DMHg和MMHg都可以被光降解，而在纯水中，在可见光照射下仅发生DMHg光降解。研究了不同环境因素对DMHg光降解的影响，并通过密度泛函理论计算和一系列控制实验阐明了其潜在机制。我们的研究结果表明，潮汐溪水中的 DMHg 降解率高于黄河、燕湖和纯净水。 NO、NO和DOM均能促进光降解，其中DOM和NO表现出特别强的积极作用。采用不同的光源，发现紫外光在 DMHg 光降解中更有效。此外，在DMHg光降解过程中检测到MMHg，证实DMHg的光化学去甲基化是阳光照射水中MMHg的来源。这项工作可能为天然水中 DMHg 的光降解提供新的机制见解，并丰富汞的全球生物地球化学循环的研究。