**5. Conclusions**

Our research confirmed that nanoparticles of AgNPs and ZnONPs spiked in NCKU Lake, Zengwun Reservoir, and Erren River cause minor toxic effects. We speculated that AgNPs and ZnONPs spiked in the natural water had a stronger aggregation and changed their physicochemical properties by interacting with the surrounding environment, which consequently mitigated their toxic effects. However, AgNPs and ZnONPs spiked in the natural water increased the mortality of zebrafish embryos and delayed hatching time in higher concentrations, as well as induced ROS, autophagy, and apoptosis.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/nano12040717/s1, Figure S1: Survival rate of zebrafish embryos exposed to original water. (**a**) The survival rate of embryos treated with original water of NCKU Lake, Zengwun Reservoir, and Erren River. Survival rates of each natural water group were high. Four mg/L 3,4-dichloroaniline (3,4 DCA) was the positive control of acute embryo toxicity assay. Survival rate of zebrafish embryos exposed to original water after passing through 1 μm, 0.45 μm, 0.22 μm, and 0.1 μm filters of (**b**) NCKU Lake, (**c**) Zengwun Reservoir, and (**d**) Erren River at 0, 24, 48, 72, and 96 hpf. hpf, hours post-fertilization; Figure S2: Body length of zebrafish embryos in original water. Body length of zebrafish embryos exposed to original water after passing through 1 μm, 0.45 μm, 0.22 μm, and 0.1 μm filters with different natural water: (**a**) NCKU Lake, (**b**) Zengwun Reservoir, and (**c**) Erren River at 72 hpf. Body length was significantly longer than MQ water in each natural water (\* *p* ≤ 0.05). Body length of zebrafish embryos were measured by View 7 software. hpf, hours post-fertilization.

**Author Contributions:** Y.-L.L.: conceptualization, data curation, methodology, writing—original draft; Y.-S.S.: investigation, methodology; Z.-Y.C.: conceptualization, methodology, data curation, validation, visualization, writing—original draft; J.-Y.L.: formal analysis, investigation; F.-Y.C. and J.-Y.L.: formal analysis, investigation, Y.-H.W.: conceptualization, methodology, writing—review and editing; Y.-J.W.: conceptualization, writing—review and editing, funding acquisition, resources. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the Ministry of Science and Technology, Taiwan (MOST 109- 2314-B-006-051-MY3), Toxic and Chemical Substances Bureau, Environmental Protection Administration, Executive Yuan, Taiwan (110A012) and the Environmental Analysis Laboratory, Environmental Protection Administration, Executive Yuan, Taiwan (Q106-P014).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** We gratefully acknowledge the National Cheng Kung University Medical College Core Research Laboratory for administrative and technical support. We also thank the Taiwan Zebrafish Technology and Resource Center and the Center for Micro/Nano Science and Technology for technical help.

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