University of Connecticut, Department of Marine Sciences, Groton, CT, USA.
University of Southern California, Earth Sciences, Los Angeles, CA, USA.
Nat Commun. 2023 Oct 23;14(1):6728. doi: 10.1038/s41467-023-42463-4.
The most critical step for methylmercury (MeHg) bioaccumulation in aquatic food webs is phytoplankton uptake of dissolved MeHg. Dissolved organic matter (DOM) has been known to influence MeHg uptake, but the mechanisms have remained unclear. Here we show that the concentration of DOM-associated thiol functional groups (DOM-RSH) varies substantially across contrasting aquatic systems and dictates MeHg speciation and bioavailability to phytoplankton. Across our 20 study sites, DOM-RSH concentrations decrease 40-fold from terrestrial to marine environments whereas dissolved organic carbon (DOC), the typical proxy for MeHg binding sites in DOM, only has a 5-fold decrease. MeHg accumulation into phytoplankton is shown to be directly linked to the concentration of specific MeHg binding sites (DOM-RSH), rather than DOC. Therefore, MeHg bioavailability increases systematically across the terrestrial-marine aquatic continuum as the DOM-RSH concentration decreases. Our results strongly suggest that measuring DOM-RSH concentrations will improve empirical models in phytoplankton uptake studies and will form a refined basis for modeling MeHg incorporation in aquatic food webs under various environmental conditions.
甲基汞（MeHg）在水生食物网中生物累积的最关键步骤是浮游植物对溶解态 MeHg 的吸收。已知溶解态有机物（DOM）会影响 MeHg 的吸收，但具体机制仍不清楚。本研究表明，DOM 中与硫醇官能团（DOM-RSH）的浓度在不同的水生系统中差异很大，决定了 MeHg 的形态和可被浮游植物利用的程度。在我们的 20 个研究点中，DOM-RSH 浓度从陆地到海洋环境降低了 40 倍，而 DOM 中典型的 MeHg 结合位点的溶解有机碳（DOC）仅降低了 5 倍。研究表明，浮游植物对 MeHg 的积累与特定 MeHg 结合位点（DOM-RSH）的浓度直接相关，而不是与 DOC 相关。因此，随着 DOM-RSH 浓度的降低，MeHg 的生物利用度在陆地-海洋水生连续体中系统地增加。我们的研究结果强烈表明，测量 DOM-RSH 浓度将提高浮游植物吸收研究中的经验模型，并为在各种环境条件下建模 MeHg 在水生食物网中的摄取提供更精细的基础。
