Natural Transformation of Zinc Oxide Nanoparticles and Their Cytotoxicity and Mutagenicity

Abstract

With rapid development of the nanoindustry, studies focusing on the transformation of nanoparticles (NPs) are required to understand their stability and toxicity after being released into the environment. Here, we characterized the physicochemical properties of ZnO NPs and found that they are naturally alkalized in the presence of air (without the addition of exogenous alkaline substances). Energy dispersive X-ray/X-ray powder diffraction/Fourier transform infrared (EDX/XRD/FTIR)/Raman spectroscopy gave evidence for the formation of hydrozincite (Zn 5 (CO 3 ) 2 (OH) 6 ) and zinc hydroxide (Zn(OH) 2 ). Further, we comparatively evaluated the cellular toxicity of pristine and alkalized ZnO NPs. Cell viability testing (colony formation) showed that alkalization time-dependently decreased cytotoxicity. Alkalized NPs exhibited mutagenicity at multiple concentrations, as shown by a CD59 gene loci mutation assay. Variations in toxicity were associated with the chemical transformation of ZnO NPs, and Zn 2+ played a key role in the mutagenicity of alkalized NPs. These results indicate that NPs are chemically transformed in the environment. These transformations result in obvious variations in toxicity, suggesting that the NP transformation process should be considered more thoroughly when evaluating toxicity.

Spatially Resolved Dissolution and Speciation Changes of ZnO Nanorods during Short-Term in Situ Incubation in a Simulated Wastewater Environment

“…4 Variations in the physicochemical properties (such as size, surface chemistry, and aggregation state) of ZnO ENMs in aqueous environmental media will generate a highly complex mixture of transformed ENMs with very varied properties and behavior. 5 Transformation of ZnO ENMs may inhibit bacterial processes within urban wastewater treatment plants (WWTPs) and may adversely affect the health of organisms in soils and waters once treated material is released back into the natural environment, 6,7 though some research indicates minimal impacts. 8 More detailed knowledge and understanding of the nature of these transformations and the time-scales over which transformations can occur is essential for predicting likely outcomes of the interactions between individual ZnO ENMs and biota and the overall implications for ecosystem health.…”

“…One of the primary pathways for environmental exposure to ZnO ENMs is via their passage through municipal sewage systems. , Current concentrations of ZnO ENMs in municipal waters are predicted to be of the order of mg L –1 . Variations in the physicochemical properties (such as size, surface chemistry, and aggregation state) of ZnO ENMs in aqueous environmental media will generate a highly complex mixture of transformed ENMs with very varied properties and behavior . Transformation of ZnO ENMs may inhibit bacterial processes within urban wastewater treatment plants (WWTPs) and may adversely affect the health of organisms in soils and waters once treated material is released back into the natural environment, , though some research indicates minimal impacts .…”

Form-Specific and Probabilistic Environmental Risk Assessment of 3 Engineered Nanomaterials (Nano-Ag, Nano-TiO2, and Nano-ZnO) in European Freshwaters

“…Given the high reactivity of ZnO and the limited stability under environmental conditions, it is expected that rapid transformation into other mineral forms such as Zn‐carbonate or Zn‐phosphate occurs. These Zn forms formed under natural conditions have a lower toxicity than pristine ZnO (Wang et al 2017 ).…”

Too small to matter? Physicochemical transformation and toxicity of engineered nTiO2, nSiO2, nZnO, carbon nanotubes, and nAg

“…Wang et al (2017a) reported that as alkalization time of nZnO in ultrapure water increased, the physical morphology of nZnO changed from distinct, cylindrical, rod-like particles to showing signs of dissolution and agglomeration, coupled by an increase in hydrodynamic size of the ENMs.Wang et al (2014) studied the aggregation of nZnO under a range of pH conditions andin the presence of HA. The authors reported that the 'z-average' hydrodynamic diameter of nZnO varied non-linearly solely with respect to pH.…”