Abstract：
Complexes with low-molecular-weight thiols are crucial species of methylmercury (MeHg) excreted by anaerobic Hg-methylating microbes, notably, MeHg-cysteine (MeHg-Cys). As MeHg-Cys diffuses into surface water, it would undergo a ligand exchange process with dissolved organic matter (DOM) under nonsulfidic conditions, inevitably altering MeHg speciation and bioavailability to phytoplankton. In this study, we investigated the competitive binding kinetics between MeHg-Cys and Suwannee River natural organic matter, and their influence on the adsorption and uptake of MeHg by the cyanobacterium, Synechocystis sp. PCC6803. Liquid chromatography-inductively coupled plasma mass spectrometry was employed to monitor the kinetics processes involving competition of DOM with Cys for MeHg binding, which revealed that competitive binding kinetics were dictated by the abundance of thiol moieties in DOM. Thiol concentrations of 0.97 and 49.34 μmol of thiol (g C)-1 resulted in competitive binding rate constant (k values) of 0.30 and 3.47 h-1, respectively. Furthermore, the time-dependent competitive binding of DOM toward MeHg-Cys significantly inhibited MeHg adsorption and uptake by cyanobacteria, an effect that was amplified by an increased thiol abundance in DOM. These findings offer valuable insights into the kinetic characteristics of MeHg\'s fate and transport, as well as their impact on bioconcentration in aquatic organisms within natural aquatic ecosystems.
摘要：
具有低分子量硫醇的络合物是厌氧汞甲基化微生物排泄的甲基汞（MeHg）的关键物种，特别是,MeHg-半胱氨酸(MeHg-Cys)。随着MeHg-Cys扩散到地表水中，它将在非硫化物条件下与溶解的有机物（DOM）进行配体交换过程，不可避免地改变了甲基汞对浮游植物的形态和生物利用度。在这项研究中,我们研究了MeHg-Cys与Suwannee河天然有机物之间的竞争结合动力学，以及它们对蓝藻吸附和吸收甲基汞的影响，集胞藻。PCC6803。液相色谱-电感耦合等离子体质谱法用于监测涉及DOM与Cys竞争以结合MeHg的动力学过程，这表明竞争性结合动力学是由DOM中硫醇部分的丰度决定的。硫醇浓度为0.97和49.34μmol的硫醇（gC）-1分别导致竞争结合速率常数（k值）为0.30和3.47h-1。此外，DOM与MeHg-Cys的时间依赖性竞争性结合显着抑制了蓝细菌对MeHg的吸附和吸收，DOM中硫醇丰度的增加放大了这种效应。这些发现为甲基汞的命运和运输的动力学特征提供了有价值的见解，以及它们对自然水生生态系统中水生生物生物浓缩的影响。
