Department of Environmental and Occupational Health, School of Public Health, Texas A&M University, College Station, Texas 77843, USA.
Chem Soc Rev. 2015 Dec 7;44(23):8410-23. doi: 10.1039/c5cs00236b. Epub 2015 Oct 5.
The synthesis, stability, and toxicity of engineered metal nanoparticles (ENPs) have been extensively studied during the past two decades. In contrast, research on the formation, fate, and ecological effects of naturally-occurring nanoparticles (NNPs) has become a focus of attention only recently. The natural existence of metal nanoparticles and their oxides/sulfides in waters, wastewaters, ore deposits, mining regions, and hydrothermal vents, as exemplified by the formation of nanoparticles containing silver and gold (AgNPs and AuNPs), Fe, Mn, pyrite (FeS2), Ag2S, CuS, CdS, and ZnS, is dictated largely by environmental conditions (temperature, pH, oxic/anoxic, light, and concentration and characteristics of natural organic matter (NOM)). Examples include the formation of nanoparticles containing pyrite, Cu and Zn-containing pyrite, and iron in hydrothermal vent black smoker emissions. Metal sulfide nanoparticles can be formed directly from their precursor ions or indirectly by sulfide ion-assisted transformation of the corresponding metal oxides under anaerobic conditions. This tutorial focuses on the formation mechanisms, fate, and toxicity of natural metal nanoparticles. Natural waters containing Ag(I) and Au(III) ions in the presence of NOM generate AgNPs and AuNPs under thermal, non-thermal, and photochemical conditions. These processes are significantly accelerated by existing redox species of iron (Fe(II)/Fe(III)). NOM, metal-NOM complexes, and reactive oxygen species (ROS) such as O2˙(-), ˙OH, and H2O2 are largely responsible for the natural occurrence of nanoparticles. AgNPs and AuNPs emanating from Ag(I)/Au(III)-NOM reactions are stable for several months, thus indicating their potential to be transported over long distances from their point of origin. However, endogenous cations present in natural waters can destabilize the nanoparticles, with divalent cations (e.g., Ca(2+), Mg(2+)) being more influential than their monovalent equivalents (e.g., Na(+), K(+)). The toxicity of NNPs may differ from that of ENPs because of differences in the coatings on the nanoparticle surfaces. An example of this phenomenon is presented and is briefly discussed.
在过去的二十年中，人们广泛研究了工程金属纳米粒子（ENPs）的合成、稳定性和毒性。相比之下，最近才成为关注焦点的是天然存在的纳米粒子（NNPs）的形成、命运和生态效应。金属纳米粒子及其氧化物/硫化物在水、废水、矿床、采矿区和热液喷口的自然存在，例如含有银和金的纳米粒子（AgNPs 和 AuNPs）、Fe、Mn、黄铁矿（FeS2）、Ag2S、CuS、CdS 和 ZnS 的形成，主要由环境条件（温度、pH 值、需氧/缺氧、光照以及天然有机物（NOM）的浓度和特性）决定。例如，含有黄铁矿、含 Cu 和 Zn 的黄铁矿以及热液喷口黑烟排放物中的铁形成纳米粒子。金属硫化物纳米粒子可以直接由其前体离子形成，也可以在厌氧条件下通过硫化物离子辅助转化相应的金属氧化物间接形成。本教程重点介绍天然金属纳米粒子的形成机制、命运和毒性。在 NOM 存在下含有 Ag(I) 和 Au(III) 离子的天然水在热、非热和光化学条件下生成 AgNPs 和 AuNPs。这些过程在现有的铁（Fe(II)/Fe(III)）氧化还原物种的作用下显著加速。NOM、金属-NOM 络合物和活性氧物质（ROS）如 O2˙(-)、˙OH 和 H2O2 是纳米粒子自然发生的主要原因。AgNPs 和 AuNPs 源自 Ag(I)/Au(III)-NOM 反应，可稳定数月，因此表明它们有可能从其起源点长距离运输。然而，天然水中存在的内源性阳离子会使纳米粒子不稳定，二价阳离子（例如 Ca(2+)、Mg(2+)）比其单价等价物（例如 Na(+)、K(+)）更具影响力。NNPs 的毒性可能与 ENPs 不同，因为纳米粒子表面的涂层不同。本文介绍并简要讨论了一个示例。
