title: Lifetime and dissolution kinetics of zinc oxide nanoparticles in aqueous media.
abstract: We have assessed the persistence and lifetime of ZnO nanoparticles (ZnO-NPs) by performing dissolution experiments in three different aqueous media. These experiments were performed at ZnO-NP concentration levels close to the solubility of zincite (∼8 μM or 650 μg l(-1) of ZnO)-a concentration that is orders of magnitude higher than current estimated relevant environmental concentrations. The kinetics were followed by voltammetry, while maintaining the pH at about 7.5 using a CO2/N2 gas mixture to remove di-oxygen interference. Our results show that, under these conditions, ZnO-NPs readily dissolve with a lifetime expectancy that does not exceed 90 min. Water chemistry, especially the presence of dissolved organic matter (DOM), plays an important role in ZnO-NP dissolution. Dissolution rates significantly increase in the presence of strong chelating agents, EDTA and L-cysteine, while the addition of polymeric DOM, such as sodium alginate, has the opposite effect. Our results suggest that ZnO-NPs are unlikely to persist in natural aqueous media and that the toxicity should be primarily related to the released Zn(2+) ions rather than effects commonly associated to the presence of nanoparticles.
authors.affiliation: Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, People's Republic of China. Northwestern University, Department of Civil and Environmental Engineering, 2145 Sheridan Road, Evanston, IL 60208-3109, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.forename: Tiezheng
authors.initials: T
authors.lastname: Tong
authors.forename: Minwei
authors.initials: M
authors.lastname: Xie
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Gaillard