| mCd Class | Description |
| mCd < 1 | Nil to very low degree of pollution |
| 1 ≤ mCd < 1.5 | Low degree of pollution |
| 1.5 ≤ mCd <2 | Moderate degree of pollution |
| 2 ≤ mCd < 3.5 | High degree of pollution |
| 35 ≤ mCd < 8 | Very high degree of pollution |