| Serial number | Cr (mg L−1) | Zn (mg L−1) | Cu (mg L−1) | Ni (mg L−1) |
|---|---|---|---|---|
| NBB-1 | 0.060 | 0.064 | 0.071 | 0.044 |
| NBB-2 | 0.016 | 0.078 | 0.075 | 0.056 |
| NBB-3 | 0.080 | 0.076 | 0.079 | 0.064 |
| NBB-4 | 0.069 | 0.077 | 0.081 | 0.070 |
| NBB-5 | 0.032 | — | 0.061 | 0.035 |
| NBB-6 | 0.043 | — | 0.061 | 0.037 |
| NBB-7 | 0.051 | — | 0.065 | 0.044 |
| NBB-8 | 0.046 | — | 0.063 | 0.032 |
| I water* | 0.01 | 0.05 | 0.01 | — |
| II water* | 0.05 | 1 | 1 | — |
| III water* | 0.05 | 1 | 1 | — |
| IV water* | 0.05 | 2 | 1 | — |
| V water* | 0.1 | 2 | 1 | — |
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