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Table 1 Classification of heavy metal modified degree of contamination (mCd), nemerow pollution index (PN), index of geo-accumulation (Igeo) and potential ecological risk

From: Hydrochemical characteristics of surface water and ecological risk assessment of sediments from settlements within the Birim River basin in Ghana

Class mCd Cont deg PN Cont deg Igeo Cont deg. RI Ecological risk
0 < 1.5 Unpolluted < 1 Unpolluted < 0 Unpolluted < 110 Low risk
1 1.5 ≤ Cd < 2 Slightly polluted 1 ≤ PN < 2.5 Slightly polluted 0–1 Slightly to moderately polluted 110 ≤ RI < 200 Moderate risk
2 2 ≤ Cd < 4 Moderately polluted 2.5 ≤ PN < 7 Moderately polluted 1–2 Moderately polluted 200 ≤ RI < 400 Considerable risk
3 4 ≤ Cd < 8 Moderately-heavily polluted ≥ 7 Heavily polluted 2–3 Moderately to highly polluted ≥ 400 Severe risk
4 8 ≤ Cd < 16 Heavily polluted    3–4 Highly polluted   
5 16 ≤ Cd < 32 Severely polluted    4–5 Highly to extremely polluted   
6 ≥ 32 Extremely polluted    5–6 Extremely polluted