Effects of Chloride and Ionic Strength on Physical Morphology, Dissolution, and Bacterial Toxicity of Silver Nanoparticles

Abstract

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.

Antibacterial activity of silver nanoparticles: A surface science insight

“…However, in presence of excess chloride, soluble silver (+1) polychloride species AgCl x (x−1)− are formed and contribute to the antibacterial activity ( Fig. 2B) [60,61]. As these species are negatively charged, it is however possible that their activity toward the cells, and notably their capability to be internalized, is different.…”

A critical review of nanohybrids: synthesis, applications and environmental implications

“…Eco-toxicity of singular NMs and their microbial and organismal uptake are known to be influenced by material-specific physicochemical properties such as size, [143] shape, [144] aggregation state, [145] surface functionality and coating, [146] reactive oxygen species (ROS) generation capability, [143,147] photoactivity, [148] crystallinity [149] and dissolution [26,145] of metal NMs and bandgap [150] of metal oxide NMs. When NMs are exposed to the environment they experience aggregation in aqueous media [25] and deposition onto solid surface [151] and porous media, [152] which contribute to their mobility in the aqueous environment.…”

Physicochemical transformation and algal toxicity of engineered nanoparticles in surface water samples

“…In addition, the dissolution of ZnO NPs was observed at both low and high pH and was enhanced by humic acid at high pH (Bian et al, 2011). The aggregation and dissolution of Ag NPs increased with increasing ionic strength (Chambers et al, 2014) but was inhibited in the presence of Cl À . CNTs demonstrated enhanced stability in the presence of DOM (Lin and Xing, 2008;Lin et al, 2010a), which was greatly dependent on pH and ionic strength as well (Lin et al, 2009(Lin et al, , 2012a.…”

“…An increasing number of studies have reported the toxicity of NPs to aquatic organisms with a focus on the effect of water chemistry (Schultz et al, 2014). The higher toxicity of Ag NPs to algal cells was observed in acidic media (Oukarroum et al, 2014) and media with high ionic strength (Chambers et al, 2014), owing to the increased release of silver ions. However, the inverse phenomenon was reported in several studies where Ag NPs demonstrated decreased toxicity in media with higher ionic strength (Gao et al, 2009;Harmon et al, 2014).…”