DataSheet1_The Transformation of Inorganic and Methylmercury in the Presence of l-Cysteine Capped CdSe Nanoparticles.docx

Transformations of mercury (Hg) forms in the aquatic environment is a crucial aspect of Hg fate, transport and the bioaccumulation of methylmercury (CH3Hg; MeHg), which is the form that drives most human health concerns. Transformations between Hg forms on surfaces have been inadequately studied but here we report on the interaction of inorganic Hg (HgII) and MeHg with chalcogenide nanoparticles (NPs); specifically L-cysteine capped CdSe nanocrystals. The study sheds light on the transformation of the Hg species and the interaction mechanisms, by examining the product composition, reaction mass balance and the distribution between the liquid and solid phase. The results showed that the quenching of the photoluminescence (PL) of CdSe NPs was greater for HgII than MeHg, and that HgII caused significant PL quenching even when its concentration was in the nM range. Over 90% of HgII was found associated with the solid phase while most MeHg existed in the liquid phase in the experimental solutions. No dimethylmercury ((CH3)2Hg; DMeHg) was produced from the interaction of MeHg and the NPs, in contrast to findings with microparticles. However, a fast and complete MeHg transformation into HgII occurred when the MeHg + NPs mixture was exposed to light. A scheme for the MeHg degradation was derived and is presented, and it was concluded that the precipitation of HgSe accelerated the MeHg degradation. These results provide insight into the abiotic pathways for MeHg degradation in environmental waters in the presence of NPs.

水环境中汞（Hg）形态的转化是汞归趋、迁移以及甲基汞（CH₃Hg; MeHg）生物富集的核心环节，而甲基汞正是引发绝大多数人类健康关切的汞形态。目前针对汞形态在界面间的转化研究仍不够充分，本工作则针对无机汞（HgII）与甲基汞和硫族化物纳米颗粒（chalcogenide nanoparticles, NPs）—— 具体为L-半胱氨酸包覆的硒化镉（CdSe）纳米晶 —— 的相互作用展开了研究。本研究通过分析产物组成、反应物料衡算以及液固两相中的汞分布情况，阐明了汞物种的转化过程与相互作用机制。实验结果显示：相较于甲基汞，无机汞对硒化镉纳米晶光致发光（photoluminescence, PL）的淬灭效果更为显著；且即便无机汞浓度处于纳摩尔（nM）级别，仍可引发显著的光致发光淬灭。在实验体系的溶液中，超过90%的无机汞会结合至固相，而绝大多数甲基汞则留存于液相。与微粒体系的研究结果不同，本实验未在甲基汞与纳米颗粒的相互作用体系中检测到二甲基汞((CH₃)₂Hg; DMeHg)的生成。然而，当甲基汞与纳米颗粒的混合体系暴露于光照环境时，甲基汞可快速且完全地转化为无机汞。本研究推导并提出了甲基汞的降解路径，并证实硒化汞（HgSe）的沉淀过程加速了甲基汞的降解。上述研究结果为环境水体中纳米颗粒存在条件下甲基汞的非生物降解途径提供了重要参考。