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Table 1 Nemerow multi-factor pollution, potential and comprehensive ecological indices.

From: Pyritic metals sequestration on mine dumps treated with oyster mushroom (Pleurotus ostreatus, Jacq.et Fr.)

Nemerow multi-factor pollution index, NIPI  
NIPI ranges Pollution grades  
≤0.7 Clean  
0.7 < NIPI ≤ 1 Cautionary  
1 < NIPI ≤ 2 Light pollution  
2 < NIPI ≤ 3 Medium pollution  
NIPI > 3 Heavy pollution  
Potential (\(E_{\text{r}}^{i}\)) and comprehensive (RI) ecological harm indices rating for the heavy metal
\(E_{\text{r}}^{i}\) range RI range Ecological pollution grades
<40 <150 Light ecological risk
40–79 150–299 Middle ecological risk
80–159 300–600 Strong ecological risk
160–320 >600 Very strong ecological risk
>320 <150 Extremely strong ecological risk