title: Influence of dissolved organic matter on photogenerated reactive oxygen species and metal-oxide nanoparticle toxicity.
abstract: The effect of humic acid (HA) or fulvic acid (FA) on reactive oxygen species (ROS) generation by six metal-oxide nanoparticles (NPs) and their toxicities toward Escherichia coli was investigated under UV irradiation. Dissolved organic matter (DOM) decreased OH generation by TiO2, ZnO, and Fe2O3, with FA inhibiting OH generation more than HA. The generated OH in NPs/DOM mixtures was higher than the measured concentrations because DOM consumes OH faster than its molecular probe. None of NPs/FA mixtures produced O2(-). The generated O2(-) concentrations in NPs/HA mixtures (except Fe2O3/HA) were higher than the sum of O2(-) concentrations that produced as NPs and HA were presented by themselves. Synergistic O2(-) generation in NPs/HA mixtures resulted from O2 reduction by electron transferred from photoionized HA to NPs. DOM increased (1)O2 generation by TiO2, CuO, CeO2, and SiO2, and FA promoted (1)O2 generation more than HA. Enhanced (1)O2 generation resulted from DOM sensitization of NPs. HA did not increase (1)O2 generation by ZnO and Fe2O3 primarily because released ions quenched (1)O2 precursor ((3)HA*). Linear correlation was developed between total ROS concentrations generated by NPs/DOM mixtures and bacterial survival rates (R(2) ≥ 0.80). The results implied the necessity of considering DOM when investigating the photoreactivity of NPs.
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China. Electronic address: junfengn@bnu.edu.cn.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Niu
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China.
authors.forename: Enxiang
authors.initials: E
authors.lastname: Shang
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, PR China; School of Civil and Environmental Engineering and the Brook Byers Institute for Sustainable Systems, Georgia Institute of Technology, Atlanta, GA 30332, United States.
authors.forename: John Charles
authors.initials: JC
authors.lastname: Crittenden
mesh_terms: D005290:Ferric Compounds; D006812:Humic Substances; D008670:Metals; D010087:Oxides; D017382:Reactive Oxygen Species; D012822:Silicon Dioxide
chemical_list: D005290:Ferric Compounds; D006812:Humic Substances; D008670:Metals; D010087:Oxides; D017382:Reactive Oxygen Species; D012822:Silicon Dioxide
keywords: Escherichia coli; Fulvic acid; Humic acid; Metal-oxide nanoparticles; Phototoxicity; Reactive oxygen species