Zinc oxide (ZnO) nanoparticles (NPs) are widely used in consumer products, but are toxic to various living organisms. Dissolution and release of zinc ions is a key step controlling NP fate, metal bioavailability and toxicity, and dissolution rates depend upon many environmental factors, including interactions with natural organic matter (NOM). The goal of this research is to study how the characteristics of NOM influence the dissolution rate of ZnO NPs. We utilized anodic stripping voltammetry to directly measure dissolved Zn ions in aqueous solution at a relatively high time resolution, and examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs (average primary particle diameter of 20-30 nm) in buffered potassium chloride solution (I = 0.1 M, pH = 8.5) at 25.0 �C. The observed dissolution rate constant (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg-C L-1) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for 16 different NOM isolates at 20 mg-C L-1, values of kobs positively correlated with certain properties of the NOM, including Specific UV Absorbance (SUVA), oxygen/carbon ratio, aromatic and carbonyl carbon contents and molecular weight (MW). Dissolution rates were negatively correlated with hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. In addition, a weak negative correlation was observed between kobs and ZnO NP aggregate size in the early stage of dissolution, which in turn is negatively correlated with MW of NOMs. Findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NP-NOM interactions.

Effects of natural organic matter properties on the dissolution kinetics of zinc oxide nanoparticles

248th National Meeting (2014)

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