**4. Conclusions**

In summary, the present study provides evidence regarding the dietary transfer of ZnO-NPs from *E. coli* OP50 to *C. elegans* and their toxic effects on locomotive behaviors and D-type GABAergic motor neurons. Additionally, these effects were found to be more significant in *C. elegans* that were fed ZnO-NPs pre-treated *E. coli* OP50 than in those exposed to ZnCl2 pre-treated *E. coli* OP50, which indicates that the neurotoxicity caused by the dietary transfer of ZnO-NPs is mostly due to nanoparticles rather than Zn2+. The results of the present study highlight the potential neurotoxicity and toxic mechanisms of ZnO-NPs transferred through food chains.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/nano13020289/s1, Figure S1: TEM image of ZnO nanoparticles (ZnO-NPs) used in this study; Figure S2 Representative images of GABAergic neurons in *C. elegans* (A–C); Figure S3. Effects of ZnO-NPs and ZnCl2 on cholinergic motor neurons.

**Author Contributions:** Conceptualization, C.M.H. and C.-W.H.; methodology, C.-W.H.; validation, C.M.H.; investigation, C.M.H. and C.-W.H.; data curation, C.-W.H.; writing—original draft preparation, C.M.H.; writing—review and editing, C.-W.H.; visualization, C.M.H.; supervision, C.-W.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Science and Technology (Taiwan), gran<sup>t</sup> number MOST104-2221-E002-034-MY3. The APC was funded by the National Kaohsiung University of Science and Technology (grant number 111TSD00-2).

**Data Availability Statement:** The data would be available on request to the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
