Table 6 Grading of contamination factor (Cf), the potential ecological risk coefficient (Er) and potential ecological risk index (PERI).
Cf | Er | PERI | Ecological risk |
|---|---|---|---|
< 1 | ≤ 40 | PERi ≤ 150 | Low contamination |
1 < Cf ≤ 3 | 40 < Er ≤ 80 | 150 < Er ≤ 300 | Moderate contamination |
3 < Cf ≤ 6 | 80 < Er ≤ 160 | 300 < Er ≤ 600 | Considerable contamination |
6 < Cf ≤ 9 | 160 < Er ≤ 320 | PERI > 600 | High risk |
Cf > 9 | Er ≥ 320 | – | Very high contamination |
