The pollution state of selected samples can be estimated by different indexes of pollution, of which the metal pollution index, MPI can be used as an indicator of the overall water quality related to heavy metals content and it is calculated by the following equation (Edet & Offiong 2002; Shehu et al. 2016):
where Ci is the measured concentration of each metal and MACi is the maximum admissible concentration of the ith metal. MPI values greater than 1 represent a threshold warning (Edet & Offiong 2002). Table 1 presents the MPI classification for water used for drinking and domestic purposes (Edet & Offiong 2002).
Table 1
Classification of water quality based on the MPI
| MPI | Characteristics class |
|---|---|
| <0.3 | Very pure I |
| 0.3–1.0 | Pure II |
| 1.0–2.0 | Slightly affected III |
| 2.0–4.0 | Moderately affected IV |
| 4.0–6.0 | Seriously affected V |
| >0.6 | Seriously affected VI |
| MPI | Characteristics class |
|---|---|
| <0.3 | Very pure I |
| 0.3–1.0 | Pure II |
| 1.0–2.0 | Slightly affected III |
| 2.0–4.0 | Moderately affected IV |
| 4.0–6.0 | Seriously affected V |
| >0.6 | Seriously affected VI |