Table 4.
Placing solubility results from Table 2 into different grouping schemes shows the importance of specifying pH
| 4a | ||
| Test material | Low pH | Neutral pH |
| Bulk-Zn metal | Biopersistent | Biopersistent |
| Nano-Zn metal | Soluble | Biopersistent |
| Bulk-ZnO | ||
| Nano-ZnO100 nm | Soluble | Biopersistent |
| Nano-ZnO50 nm | ||
| Bulk-anatase | ||
| Nano-anatase | Biopersistent | Biopersistent |
| Bulk-rutile | ||
| Nano-rutile | ||
| 4b | ||
| Solubility category | Low pH | Neutral pH |
| High solubility (>70 %) | Bulk-ZnO (88.5 %) | |
| Nano-ZnO100 nm (97 %) | ||
| Nano-ZnO50 nm (94 %) | ||
| Nano-Zn metal (80.8 %) | ||
| Moderate solubility (10–70 %) | Bulk-Zn metal (17.5 %) | |
| Low solubility (1–10 %) | Nano-Zn metal (1.33 %) | |
| Bulk-Zn metal (2.05 %) | ||
| Nano-ZnO50 nm (2.13 %) | ||
| Nano-ZnO100 nm (1.87 %) | ||
| Negligible solubility (<1 %) | Bulk-ZnO (0.95 %) | |
| Bulk-anatase (0.019 %) | Bulk-anatase (<0.0001 %) | |
| Nano-anatase (0.022 %) | Nano-anatase (<0.0001 %) | |
| Bulk-rutile (0.0001 %) | Bulk-rutile (<0.0001 %) | |
| Nano-rutile (0.0002 %) | Nano-rutile (<0.0001 %) | |