| Heavy metals | Not polluted | Moderately polluted | Heavily polluted |
| Mn | <300 | 300 - 500 | >500 |
| Fe | ND | ND | ND |
| Cr | <25 | 25 - 75 | >75 |
| Cu | <25 | 25 - 50 | >50 |
| Ni | <20 | 20 - 50 | >50 |
| As | <3 | 3 - 8 | >8 |
| Zn | <300 | 300 - 600 | >600 |
| Pb | <40 | 40 - 60 | >60 |
| Cd | -- | <6 | >6 |