Complete transformation of ZnO and CuO nanoparticles in culture medium and lymphocyte cells during toxicity testing

Abstract

Here, we present evidence on complete transformation of ZnO and CuO nanoparticles, which are among the most heavily studied metal oxide particles, during 24 h in vitro toxicological testing with human T-lymphocytes. Synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy results revealed that Zn speciation profiles of 30 nm and 80 nm ZnO nanoparticles, and ZnSO₄- exposed cells were almost identical with the prevailing species being Zn-cysteine. This suggests that ZnO nanoparticles are rapidly transformed during a standard in vitro toxicological assay, and are sequestered intracellularly, analogously to soluble Zn. Complete transformation of ZnO in the test conditions was further supported by almost identical Zn spectra in medium to which ZnO nanoparticles or ZnSO₄ was added. Likewise, Cu XANES spectra for CuO and CuSO₄-exposed cells and cell culture media were similar. These results together with our observation on similar toxicological profiles of ZnO and soluble Zn, and CuO and soluble Cu, underline the importance of dissolution and subsequent transformation of ZnO and CuO nanoparticles during toxicological testing and provide evidence that the nano-specific effect of ZnO and CuO nanoparticles is negligible in this system. We strongly suggest to account for this aspect when interpreting the toxicological results of ZnO and CuO nanoparticles.

Keywords:

• Copper oxide
• zinc oxide
• nanoparticles
• speciation
• mammalian cells

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

Financial support from SA Government PRIF program project “International Cluster on Nanosafety” and SUN project Funded by the European Commission (Grant agreement no. 604305) are kindly acknowledged. N.H.V. holds an Alexander von Humboldt Fellowship for Experienced Researchers. A.I is currently funded by Estonian Research Council grants PUT748 and SA Archimedes EQUiTANT. Although EPA contributed to this article, the views, interpretations, and conclusions expressed in this article are solely those of the authors and do not necessarily reflect or represent EPA?s views or policies. This research used resources of the Department of Energy and the MRCAT member institutions, Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.