Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
Environ Sci Technol. 2014;48(1):761-9. doi: 10.1021/es403969x. Epub 2013 Dec 23.
In this study, we comprehensively evaluate chloride- and ionic-strength-mediated changes in the physical morphology, dissolution, and bacterial toxicity of silver nanoparticles (AgNPs), which are one of the most-used nanomaterials. The findings isolate the impact of ionic strength from that of chloride concentration. As ionic strength increases, AgNP aggregation likewise increases (such that the hydrodynamic radius [HR] increases), fractal dimension (Df) strongly decreases (providing increased available surface relative to suspensions with higher Df), and the release of Ag(aq) increases. With increased Ag(+) in solution, Escherichia coli demonstrates reduced tolerance to AgNP exposure (i.e., toxicity increases) under higher ionic strength conditions. As chloride concentration increases, aggregates are formed (HR increases) but are dominated by AgCl(0)(s) bridging of AgNPs; relatedly, Df increases. Furthermore, AgNP dissolution strongly increases under increased chloride conditions, but the dominant, theoretical, equilibrium aqueous silver species shift to negatively charged AgClx((x-1)-) species, which appear to be less toxic to E. coli. Thus, E. coli demonstrates increased tolerance to AgNP exposure under higher chloride conditions (i.e., toxicity decreases). Expression measurements of katE, a gene involved in catalase production to alleviate oxidative stress, support oxidative stress in E. coli as a result of Ag(+) exposure. Overall, our work indicates that the environmental impacts of AgNPs must be evaluated under relevant water chemistry conditions.
在这项研究中，我们全面评估了氯离子和离子强度对银纳米颗粒（AgNPs）物理形态、溶解和细菌毒性的影响，AgNPs 是应用最广泛的纳米材料之一。研究结果将离子强度的影响与氯离子浓度的影响分离开来。随着离子强度的增加，AgNP 的聚集也随之增加（使得水动力半径[HR]增加），分形维数（Df）强烈降低（与具有更高 Df 的悬浮液相比，提供了更多的可用表面），Ag(aq) 的释放也增加。随着溶液中 Ag+浓度的增加，大肠杆菌在更高离子强度条件下对 AgNP 暴露的耐受性降低（即毒性增加）。随着氯离子浓度的增加，形成了聚集体（HR 增加），但主要是 AgNPs 之间的 AgCl(0)(s)桥接；相关地，Df 增加。此外，在增加氯离子条件下，AgNP 的溶解强烈增加，但主要的、理论上的、平衡的水合银物种向带负电荷的 AgClx((x-1)-)物种转移，这些物种似乎对大肠杆菌的毒性较小。因此，大肠杆菌在较高氯离子条件下对 AgNP 暴露的耐受性增加（即毒性降低）。与过氧化氢酶生产有关的 katE 基因的表达测量结果表明，Ag(+) 暴露导致大肠杆菌产生氧化应激。总的来说，我们的工作表明，必须在相关的水化学条件下评估 AgNPs 的环境影响。
