The difficulties when studying the behavior of engineered nanoparticles (ENPs), and the subsequent metal speciation in aquatic ecosystems, at environmentally relevant concentrations (i.e., ppt level) are often related to the occurrence of ENP constitutive elements at high concentrations as a background in aquatic media. In this study, the physicochemical behavior of CdSe/ZnS quantum dots (QDs) when spread at very low concentrations in surface waters was investigated. The above-mentioned issues were overcome with the use of isotopically labeled QDs, separated by centrifugal ultrafiltration (CU) and measured by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), combined with the detection of free and labile metal ions by scanned stripping chronopotentiometry (SSCP). They firmly provided a thorough comprehension regarding the transformation of QDs in surface waters. The physicochemical conditions of the medium including the presence of an analog of natural organic matter and a mineral (i.e., fulvic acid and goethite), the manufactured coating of the QDs [here thioglycolic acid (TGA)], and the occurrence of added Zn in the medium were considered in the study. The overall results show that, in the absence of mineral/organic matter, the TGA ligands in solution that detached from the QD surface after dissolution control the metal speciation, especially for Cd. Conversely, in a more representative aquatic ecosystem condition (i.e., with Zn in the background media together with fulvic acid and goethite), almost no Zn or Cd dissolution from the QDs is detected. SSCP measurements reveal that the Zn complexes formed with the organic/mineral material in the system are inert, whereas the speciation model calculations indicated that Cd2+ is bound to TGA ligands in solution and organic/inorganic matter—therefore suggesting that, under the studied conditions, aquatic organisms will be exposed to a very low concentration of free and labile metal ions issued from the QDs.

中文翻译：

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地表水中工程纳米粒子（CdSe/ZnS 量子点）的地球化学

在研究环境相关浓度（即 ppt 水平）的工程纳米粒子 (ENP) 的行为以及随后的水生生态系统中的金属形态时，遇到的困难通常与作为背景的高浓度 ENP 组成元素在水生生态系统中的出现有关。媒体。在这项研究中，研究了 CdSe/ZnS 量子点 (QD) 在地表水中以非常低的浓度扩散时的物理化学行为。通过使用同位素标记的 QD，通过离心超滤 (CU) 分离并通过高分辨率电感耦合等离子体质谱 (HR-ICP-MS) 进行测量，结合游离和不稳定金属的检测，克服了上述问题离子通过扫描剥离计时电位法 (SSCP)。他们坚定地提供了对地表水中量子点转化的透彻理解。介质的物理化学条件包括天然有机物质和矿物质的类似物（即富里酸和针铁矿）的存在，量子点的制造涂层 [此处为巯基乙酸 (TGA)]，以及添加的锌的出现研究中考虑了介质。总体结果表明，在没有矿物/有机物质的情况下，溶解后从 QD 表面分离的溶液中的 TGA 配体控制了金属形态，尤其是对于 Cd。相反，在更具代表性的水生生态系统条件下（即背景介质中含有 Zn 以及富里酸和针铁矿），几乎没有检测到 QD 中的 Zn 或 Cd 溶解。