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

目的：研究纳米银在自然环境中的暴露途径、去向和风险。这一提议的目的是解决两个假设：(1)纳米银可以通过动力学限制的氧化过程在环境中进行完全的反应溶解。纳米银将在含有溶解氧的环境隔间中以颗粒形式非持久存在，但在缺氧舱或含有还原剂的生物基质中持久存在。(2)反应溶解速率将显著依赖于NAG颗粒大小、表面状态(配体、涂层)和介质组成，需要在复杂介质和生物组织中进行详细的实验，以便为生命周期风险评估做出有用的预测。该项目将进行四项任务：(1)开发环境中纳米银的来源和材料流动的第一代模型，考虑动态溶解行为；(2)纳米银溶解的详细动力学和机理，考虑附着在颗粒表面、涂层、近颗粒环境的组成和表面氧化状态的稳定配体的影响；(3)银在生物隔室中的分布和纳米颗粒的持久性，通过使用非洲爪哇生物的实验，非洲爪哇是水生系统中用作模式哨兵物种的两栖动物，非常容易受到环境污染物的影响，非常适合研究纳米银的生物分布和持久性。(4)差异化纳米风险集成模型开发与分析。智力优势：这项建议将找到解决由于纳米含银产品被清洗、磨损或丢弃而产生的一些毒性问题，银可以以纳米颗粒、纳米颗粒聚集体或可溶离子的形式进入环境。据报道，银对一些水生生物具有高度毒性，作为一种抗生素，也可能破坏或改变环境中有益的微生物群落。众所周知，银在浮游植物和一些海洋无脊椎动物中也会生物积累，并已被证明对斑马鱼胚胎具有高度毒性。更广泛的影响这个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的潜在环境影响。该项目的主要成果将是纳米银暴露路径的概念模型，从而能够估计银在各种环境隔间中的位置、形式和浓度。这项工作将提供与政策相关的信息，以帮助界定“不同的纳米风险”，其定义是纳米银在多大程度上有可能造成环境风险，而不是那些根据来源条件和以往经验以及传统银形式的数据容易评估的风险。这是一个关键的监管问题，它决定了NAG是需要作为纳米风险进行特殊考虑，还是可以作为传统的银离子释放来处理。最后，深入了解Ag+释放动力学和机制将有助于开发控释制剂，优化NAG的使用，避免材料浪费和真核毒性作为抗菌医疗产品的副作用。

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.