Exposure Pathways, Dissolution Kinetics, and Fate of Nano-Silver in the Environment

摘要目的：研究纳米银在自然环境中的暴露途径、命运和风险。本提案的目的是解决两个假设：(1)纳米银可以通过动力学限制氧化过程在环境中进行完全的反应性溶解。纳米银在含有溶解氧的环境隔间中不以粒子形式存在，但在缺氧隔间或含有还原剂的生物基质中存在。(2)反应性溶解速率将显示出对nAg颗粒大小、表面状态（配体、涂层）和介质组成的显著依赖，这需要在复杂介质和生物组织中进行详细的实验，以便对生命周期风险评估做出有用的预测。该项目将分四项任务进行：(1)建立了第一代环境中纳米银的来源和物质流动模型，用于解释动态溶解行为；(2)详细的纳米银溶解动力学和机制，用于解释附着在颗粒表面的稳定配体、涂层、近颗粒环境的组成和表面氧化状态的影响；(3)银在生物隔间中的分布和纳米粒子的持久性；通过对非洲爪蟾（Xenopus laevis）进行实验，非洲爪蟾是一种两栖动物，是水生系统中对环境污染物高度敏感的模式哨兵物种，非常适合研究纳米银的生物分布和持久性；(4)综合模型开发和差异纳米风险分析。知识价值：本提案将找到一些毒性问题的解决方案，这些问题是由于含纳米银的产品被洗涤，磨损或丢弃，银可以以纳米颗粒，纳米颗粒聚集体或可溶性离子的形式进入环境。据报道，银对一些水生生物有剧毒，作为抗生素也可能损害或改变环境中的有益微生物群落。银也会在浮游植物和一些海洋无脊椎动物体内生物积累，并已被证明对斑马鱼胚胎有剧毒。更广泛的影响该项目解决了当前市场上产量最高的纳米技术产品之一——纳米银对环境的潜在影响。这个项目的主要成果将是一个纳米银暴露途径的概念模型，允许在各种环境隔间中估计银的位置、形式和浓度。这项工作将提供与政策相关的信息，以帮助定义“差异纳米风险”，其定义是纳米银可能造成的环境风险的程度，超出了从来源条件和传统银形式的先前经验和数据容易估计的风险。这是一个关键的监管问题，它决定了nAg是否需要作为纳米风险来特殊考虑，还是可以作为传统的Ag离子释放来处理。最后，深入了解Ag+释放动力学和机制将有助于开发控释配方，优化Ag的使用，避免作为抗菌医疗产品副作用的材料浪费和真核毒性。

AbstractProposal 1057547Objective:This project focuses on the exposure pathways, fate, and risk of nano-silver in the natural environment. The objective of this proposal is to address two hypothesis: (1) nano-silver can undergo complete reactive dissolution in the environment through kinetically limited oxidation processes. Nano-silver will be non persistent in particle form in environmental compartments containing dissolved oxygen, but persistent in anoxic compartments or in biological matrices containing reducing agents. (2) Reactive dissolution rates will show significant dependence on nAg particle size, surface state (ligands, coatings) and media composition, requiring detailed experimentation in complex media and biological tissue to make useful predictions for life-cycle risk assessment. The project will proceed in four tasks: (1) development of a first generation model of sources and materials flows of nano-silver in the environment accounting for dynamic dissolution behavior, (2) detailed kinetics and mechanisms of nanosilver dissolution, accounting for the effects of stabilizing ligands attached to the particle surfaces, coatings, composition of the near-particle environment, and surface oxidation state, (3) silver distribution and nanoparticle persistence in biological compartments, through experiments using the organism Xenopus laevis, an amphibian used as a model sentinel species in aquatic systems that is highly vulnerable to environmental pollutants and well suited to the study of nanosilver biodistribution and persistence, and (4) integrated model development and analysis to differential nano-risk. Intellectual merit: This proposal will find solutions to some of the toxicity issues as a result of nano-silver-containing products are washed, abraded, or discarded, silver can enter the environment either as nanoparticles, nanoparticle aggregates, or soluble ions. Silver is reported to be highly toxic to some aquatic organisms, and as an antibiotic may also damage or alter beneficial microbial communities in the environment. Silver is also known to bioaccumulate in phytoplankton and some marine invertebrates and has been shown to be highly toxic to zebrafish embryos. Broader Impacts This project addresses the potential environmental impacts of one of the highest production volume nanotechnology products on the current market: nano-silver. The main result of this project will be a conceptual model of nano-silver exposure pathways, allowing estimation of the location, forms, and concentrations of silver in a variety of environmental compartments. The work will provide policy-relevant information to help define the "differential nano-risk" defined as the extent to which nano-silver has the potential to pose environmental risks beyond those easily estimable from source terms and prior experience and data on conventional silver forms. This is a key regulatory issue that governs whether nAg requires special consideration as a nano-risk or can be treated as a conventional Ag ion release. Finally, insight into Ag+ release kinetics and mechanisms will and aid in the development of controlled release formulations that optimize the use of nAg and avoid material waste and eukaryotic toxicity as a side effect of antibacterial medical products.