Table 1 Combinations of divalent metal cations in a factorial design of experiment (Fig. 7)
| Combination | Copper | Zinc | Nickel | Log difference | |
|---|---|---|---|---|---|
| Unfiltered | Filtered | ||||
| Center point | Mid | Mid | Mid | − 2.62 | − 3.76 |
| A | High | High | High | − 3.57 | − 4.72 |
| B | Low | High | High | − 1.23 | − 1.24 |
| C | High | Low | High | − 3.26 | − 4.79 |
| D | Low | Low | High | − 0.52 | − 1.23 |
| E | High | High | Low | − 3.02 | − 4.81 |
| F | Low | High | Low | − 0.04 | − 0.01 |
| G | High | Low | Low | − 3.42 | − 4.78 |
| H | Low | Low | Low | 0.00 | − 0.01 |