Solubility of nano‐zinc oxide in environmentally and biologically important matrices

Abstract

Increasing manufacture and use of engineered nanoparticles (NPs) is leading to a greater probability for release of ENPs into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles (ZnO), dissolution to Zn2+, or some combination thereof. The goal of this study was to determine the relative solubilites of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18– 7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (~5 mg/L), but much more dissolution was observed in Dulbecco’s Modified Eagle’s Medium (DMEM), where the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low zinc solubility, likely due to precipitation of a zinc carbonate solid phase. Precipitation of a zinc-containing solid phase in RPMI also appeared to limit zinc solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on zinc solubility due to precipitation of less soluble solid phases.

Emerging patterns for engineered nanomaterials in the environment: a review of fate and toxicity studies

“…Surface charge and aggregation tend to vary with pH, where the further the environmental pH is from the ENM's PzC, the farther the surface charge is from zero. This increases their stability, since like charges will repel Judy et al 2011;Reed et al 2012;Wang et al 2011). However, high IS can minimize the forces keeping NPs separate and cause aggregation and sedimentation (French et al 2009;Handy et al 2008) even for a pH that is far from the PzC.…”

“…Conversely, the zeta potential for TiO 2 at 10 mM CaCl 2 is close to zero at pH 7 (Petosa et al 2012). The zeta potential for ZnO seems to vary significantly from very positive to very negative at pH values ranging from 4 to 10 (Jiang et al 2009a, b;Petosa et al 2012;Reed et al 2012). The zeta potentials for Au and Cu/CuO tend to be close to zero for a pH between 5.5 and 8.5, except in groundwater for Au and in algal growth media for Cu/CuO (Griffitt et al 2008;Hitchman et al 2013;Judy et al 2011;Wang et al 2011).…”

“…With the exception of ZnO in seawater (Fairbairn et al 2011;Li et al 2013;Miller et al 2010;Xia et al 2008) and freshwater (Franklin et al 2007;Li et al 2013;Mortimer et al 2010;Reed et al 2012), NP dissolution is generally slow, occurring over the course of weeks or months, if at all. Dissolution of ZnO is highly pH dependent and the presence of phosphate can significantly alter the rate of dissolution so that it can be either very high or very low (Blinova et al 2010;Montes et al 2012).…”

Metal oxide nanoparticles interact with immune cells and activate different cellular responses

“…22,27,28 In order to assess whether the effect induced by ZnO Nps on Jurkat cells was due to the Np itself or to the Zn 2+ ions released by the particles, the cells were exposed to ZnCl 2 salt at three different concentrations (1, 10, and 100 µg/mL Zn 2+ ) and the MAPK and NFκB activation was assessed in Western blots.…”

Influence of Dissolution on Fate of Nanoparticles in Freshwater

“…For example, titanium dioxide nanoparticles (nano-TiO 2 ) were assumed to be practically insoluble in freshwater in many studies, [8], [9] while they were confirmed being able to dissolve in acid aqueous NaCl solutions (pH < 3) at temperatures of 25 and 37 ℃. [10] Dissolution of zinc oxide nanoparticles (nano-ZnO) was observed with 7.18-7.40 mg/L dissolved Zn in pure water, but with much higher dissolved Zn concentration (> 34 mg/L) in a cell culture medium [11].…”