Influence of Aqueous Media on the ROS-Mediated Toxicity of ZnO Nanoparticles toward Green Fluorescent Protein-Expressing Escherichia coli under UV-365 Irradiation

Abstract

The aqueous media could affect the physicochemical properties (e.g., surface charge, morphology, and aggregation) of ZnO nanoparticles (nZnO), leading to their different environmental impacts. In this study, the toxicity of nZnO toward the green fluorescent protein-expressing Escherichia coli cells under UV-365 light irradiaiton in various media was assessed, including deionized (DI) water, 0.85% NaCl, phosphate-buffered saline (PBS), minimal Davis medium (MD), and Luria-Bertani medium (LB). The toxicity of nZnO was assessed by the conventional plate count method and the fluorescence intensity method, which consistently demonstrated that the nZnO toxicity was dependent on the medium components that varied the potency of reactive oxygen species (ROS) generation. In DI, NaCl, PBS, and MD medium, nZnO generated three types of ROS (O2(•-), •OH, and (1)O2), whereas in LB medium, nZnO generated O2(•-) and (1)O2. The total concentrations of ROS generated by nZnO in DI, NaCl, PBS, MD, and LB were 265.5 ± 15.9, 153.6 ± 8.6, 144.3 ± 6.9, 123.0 ± 6.0, and 115.6 ± 4.5 μM, respectively. Furthermore, a linear correlation was established between the total concentrations of three types of ROS generated by nZnO and their bacterial mortality rate (R(2) = 0.92) in various media. Since the released Zn(2+) from nZnO under UV irradiation only accounted for less than 10% of the total Zn in all media, the ionic forms of zinc did not significantly contribute to the overall toxicity. This work aims at providing further insight into the medium type influences on the ROS production and the toxicity of nZnO toward the E. coli cells.

Evaluation of nano-specific toxicity of zinc oxide, copper oxide, and silver nanoparticles through toxic ratio

“…Nevertheless, this oversimplified comparison did not consider the dose or solubility ratios. In most cases, the solubility percentages of ZnO NPs were less than 30 %, and only an applied dose of lower than 1 mg/L ZnO NPs could be completely dissolved within 8 h (Bian et al 2011;Li et al 2014). Considering only 10 % of NPs dissolved in most toxicity assays, when the metal salts exerted 10 times higher hazard effects than NPs, based on the log T e ion = −1 threshold, we conclude that the detected nanotoxicity is dependent on the released ions.…”

“…Similarly, the log T e ion values were calculated using Eq. 4, assuming that only 10 % of NPs dissolved during toxic assays (Bian et al 2011;Li et al 2014;Yu et al 2011). Definitely, metal (oxide) NPs will differ in dissolution under different environmental conditions.…”

“…The −1 threshold of log T e ion values was proposed to determine whether the toxic mechanism of NPs was dependent on its released ions. This was based on the assumption that the NPs had an approximately 10 % dissolution rate in deionized water (Bian et al 2011;Li et al 2014;Yu et al 2011). Nearly 10 % of NPs (at the concentration of nominal EC 50 ) dissolved in the short-term bioassay (6 h), while more than 95 % of the NPs dissolved in the long-term bioassay (see Fig.…”

Adsorption of MS2 on oxide nanoparticles affects chlorine disinfection and solar inactivation

“…The MS2 concentrations in the presence of 10 mg L À1 NPs were all reduced compared with the dark control. In particular, TiO 2 and ZnO NPs both displayed strong MS2 inactivation compared with the solar exposure control, probably because of their ability to generate ROS under UV excitation (Li et al, 2014(Li et al, , 2012b. Common radical species are hydroxyl radicals (OH), singlet oxygen (…”

“…Assessment of the fate of NPs in the conventional water treatment processes and potential impacts on drinking water systems is still the major task for securing sustainability of nanotechnology. On the other hand, positive benefits of engineered NPs are also highlighted by many studies, which incorporated metallic NPs (e.g., nanosilver) to remove pathogenic microorganisms (Li et al, 2008a(Li et al, , 2014. Particularly, many metal NPs and carbonaceous nanomaterials such as fullerene are capable of deactivating viruses or bacteriophages mainly due to the ability to generate reactive oxygen species (ROS) when irradiated by UV light (Cho et al, 2009;Li et al, 2012b;Zhang et al, 2013).…”