Enxiang Shang

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

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.

Photochemical transformation and photoinduced toxicity reduction of silver nanoparticles in the presence of perfluorocarboxylic acids under UV irradiation.

The impact of perfluorocarboxylic acids (PFCAs) with carbon chain length C2 to C8 on the dissolution, aggregation, reactive oxygen species (ROS) generation, and toxicity of citrate-coated AgNPs was investigated under UV irradiation. The presence of PFCAs decreased dissolution, aggregation, ROS generation, and toxicity of AgNPs because the negatively charged PFCAs sorbed on AgNP surface enhanced their stability. Both dissolution and aggregation rate of AgNPs decreased with chain length of PFCAs under UV irradiation, primarily because PFCAs with longer chain length sorbed on AgNP surface could form thicker coatings. The dissolution of AgNPs followed pseudo-first-order kinetics, and the rate constant decreased from 0.58 h(-1) with C2 to 0.30 h(-1) with C8. The hydrodynamic diameters of AgNPs linearly increased under UV irradiation with aggregation rates ranged from 72.1 to 143.5 nm/h. O2(•-) generation was observed in AgNP suspension with quantum yield of 0.12%, but was completely suppressed by PFCAs because they inhibited the interaction between photoelectrons and O2. A linear correlation was established between dissolved Ag(+) and bacterial survival rates of AgNPs with and without PFCAs under UV irradiation. This study highlights the necessity of considering coexisting organic contaminants when investigating the environmental behaviors of AgNPs.

Effects of nitrate and humic acid on enrofloxacin photolysis in an aqueous system under three light conditions: kinetics and mechanism

for enrofloxacin (Enro), which is a hazard for humans and other living organisms. The effects of NO3 and humic acid on Enro photolysis were found to be light-source dependent. These results are of significance toward the goal of providing insight into the transformation and fate of Enro in the environment. Abstract. Thelight-source-dependenteffectsofNO3 andhumicacid(HA)onenrofloxacin(Enro)photolysiskineticsin aqueous solutions were investigated under solar, UV-254 and UV-365 lamp irradiation. NO3 was found to suppress Enro photolysis through competitive photoabsorption under UV-365 irradiation, whereas it accelerated Enro photolysis under UV-254 and solar irradiation as a result of NO3 photosensitisation. Similarly, HA enhanced, inhibited or had no obvious effect on Enro photolysis under different light irradiation conditions. Even under the same light irradiation conditions, the effectofHAonEnrophotolysisvariedwithHAconcentration.Thereactiveoxygenspecies(ROS)scavengerexperiments demonstrated that Enro photolysis undergoesOH- and 1 O2-mediated self-sensitised photolysis. The photolysis pathway of Enro involved decarboxylation, defluorination and piperazinyl N 4 -dealkylation reactions. The toxicity towards Vibrio fischeri luminescent bacteria under solar irradiation was different from that under UV irradiation. The 90-min toxicity of Enro and its photoproducts increased under solar irradiation but decreased under UV-365 and UV-254 irradiation comparedtotheinitialEnrotoxicity,whichindicatedthatUVlightnotonlyhadhigherphotolysisefficiencybutalsoposed less toxicity towards bacteria than solar. Additional keyword: photoproducts, sunlight, toxicity, UV light. Received 23 October 2013, accepted 11 March 2014, published online 10 June 2014

Relative importance of humic and fulvic acid on ROS generation, dissolution, and toxicity of sulfide nanoparticles

In this study, the effect of natural organic matter (NOM) composition (humic acid (HA) or fulvic acid (FA)) on dissolution, reactive oxygen species (ROS) generation, and toxicity of sulfide nanoparticles (NPs) was investigated under UV irradiation. NOM acted as a UV filter or antioxidant, decreasing ROS (O2-, OH, and 1O2) generation by WS2 and MoS2 NPs. The higher light-absorbing fractions of HA in NP/HA mixtures and the faster reaction rate of HA with ROS resulted in higher inhibition effect of HA than FA on O2- and OH generation by WS2 and MoS2 NPs. Both HA and FA completely inhibited 1O2 generation by WS2 and MoS2 NPs. NOM could transfer electrons to CdS and promote its O2- generation. No measurable amount of OH was generated by CdS with or without NOM. FA decreased 1O2 generation by CdS more significantly than HA due to the higher reaction rate between FA and 1O2. HA showed a higher inhibition effect on the dissolution rate of CdS and WS2 NPs than FA. Both HA and FA played minor roles in the toxicity of CdS toward Escherichia coli but decreased the toxicity of MoS2 and WS2 due to the reduced ROS generation and/or dissolution concentrations.

Effect of aqueous media on the copper-ion-mediated phototoxicity of CuO nanoparticles toward green fluorescent protein-expressing Escherichia coli.

Quantitative comparison of different aqueous media on the phototoxicity of copper oxide nanoparticles (CuO NPs) is crucial for understanding their ecological effects. In this study, the phototoxicity of CuO NPs toward the green fluorescent protein-expressing Escherichia coli (GFP-E. coli) under UV irradiation (365 nm) was investigated in Luria-Bertani medium (LB), NaCl solution, deionized water (DI) and phosphate-buffered saline (PBS). The phototoxicity of CuO NPs toward GFP-E. coli decreased in the order of DI>NaCl>PBS>LB because of different released concentrations of Cu(2+). The 3h released Cu(2+) concentrations by 10mg/L CuO NPs in DI water, NaCl solution, LB medium, and PBS were 1946.3 ± 75.6, 1242.5 ± 47.6, 1023.4 ± 41.2, and 1162.1 ± 41.9 μg/L, respectively. Transmission electron microscope and laser scanning confocal microscope images of E. coli exposed to CuO NPs demonstrated that the released Cu(2+) resulted in fragmentation of bacterial cell walls, leakage of intracellular components, and finally death of bacteria in four media after UV light irradiation. In each medium, the bacterial mortality rate logarithmically increased with the releasing concentrations of Cu(2+) by CuO NPs (R(2)>0.90) exposed to 3h UV light. This study highlights the importance of taking into consideration of water chemistry when the phototoxicity of CuO NPs is assessed in nanotoxicity research.

Photocatalytic degradation of perfluorooctanoic acid over Pb-BiFeO3/rGO catalyst: Kinetics and mechanism

Degradation of perfluorooctanoic acid (PFOA) is important because of its global distribution, persistence and toxicity to organisms. In this work, the PbBiFeO3 photocatalyst was prepared by the hydrothermal method. The effect of doping amount of reduced graphene oxide (rGO) on the decomposition of PFOA was investigated under 254 nm UV light. The results indicated that 100 mg L-1 PbBiFeO3 with 0.5 wt% rGO exhibited the highest degradation efficiency for 50 mg L-1 PFOA at pH = 2.0 from aqueous solution. The removal rate of PFOA reached 69.6% after 8 h UV irradiation under the optimal conditions (PFOA concentration of 50 mg L-1, Pb BiFeO3/0.5% rGO concentration of 100 mg L-1, and pH of 2.0). The total organic carbon removal rate and defluorination rate were 28.0% and 37.6%, respectively. During the degradation process, four major intermediates with shorter chain length than PFOA (∼C4C7) were identified. The mechanism responsible for PFOA decomposition was supposed that OH attacked PFOA to form perfluoroalkyl alcohol and then was transferred to perfluoroalkyl fluoride which can easily undergo hydrolysis to form shorter-chain perfluorocarboxylic acids than PFOA. This indicated that the photocatalytic degradation of PFOA was an oxidation process through stepwise losing of CF2 group.