Methylmercury (MeHg), a highly neurotoxic substance, accumulates in aquatic food webs, and is enriched in odd isotopes (i.e., ¹⁹⁹Hg and ²⁰¹Hg), purportedly as a result of abiotic photodegradation in surface waters. Here, we highlight the potential role of phytoplankton in the mass independent fractionation (MIF) of MeHg in marine food-webs by providing evidence of (1) degradation of intracellular MeHg and reduction of intracellular inorganic mercury (Hg(II)) in the marine microalga, Isochrysis galbana; (2) a large, positive MIF (Δ¹⁹⁹Hg_reactant – Δ¹⁹⁹Hg_product ∼ 5–10‰) during intracellular degradation of MeHg in cells exposed to visible light with no UVB, consistent with the accumulation of odd isotope-enriched MeHg in marine food-webs; and (3) a negative MIF (−1‰) during intracellular reduction of Hg(II) in the presence of UVB light. If representative of the photochemical reactivity of MeHg in marine phytoplankton, our results indicate that algal cell-mediated demethylation of MeHg by visible light could account for 20 to 55% of the total photochemically driven demethylation in the open ocean and transparent freshwater ecosystems with deep euphotic zones. Thus, our results extend the importance of phytoplankton (and possibly other light permeable microorganisms) in mercury biogeochemistry beyond their role as accumulators of MeHg and/or reducers of Hg(II) at the base of the food chain to include MeHg degradation and MIF of Hg in sunlit layers of the ocean and other aquatic systems.

中文翻译：

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海洋微藻中的微生物的可见光诱导光诱导的磁质量分数分离汞

甲基汞（MeHg）是一种高度神经毒性的物质，蓄积在水生食物网中，据称由于地表水中的非生物光降解而富含奇数种同位素（即¹⁹⁹ Hg和²⁰¹ Hg）。在这里，我们通过提供（1）海洋中细胞内MeHg降解和细胞内无机汞（Hg（II））降解的证据，突出浮游植物在海洋食物网中MeHg的质量独立分级分离（MIF）中的潜在作用。微藻，等鞭金藻; （2）一个大的正MIF（Δ ¹⁹⁹汞柱_反应物- Δ ¹⁹⁹汞柱_产物暴露于无紫外线的可见光的细胞内，甲基汞的细胞内降解过程中约5-10‰），这与海洋食物网中奇异同位素富集的甲基汞的积累是一致的；（3）在存在UVB光的情况下，细胞内Hg（II）还原过程中的MIF负值（-1‰）。如果能代表海洋浮游植物中MeHg的光化学反应性，我们的结果表明，藻类细胞介导的MeHg脱甲基化作用可占开放海洋和深层富营养化的透明淡水生态系统中光化学驱动脱甲基化作用总量的20％至55％。区域。因此，