Table 4.

Classification of Potential Ecological Risk Index (Håkanson 1980)

Level of potential ecological risk	${\mathit{Er}}^i$ value	Level of ecological risk	$\mathrm{RI}$ value
Low	${\mathit{Er}}^i$< 40	Low	RI < 150
Moderate	40 ≤ ${\mathit{Er}}^i$< 80	Moderate	150 ≤ RI < 300
Considerable	80 ≤ ${\mathit{Er}}^i$< 160	Considerable	300 ≤ RI < 600
High	160 ≤ ${\mathit{Er}}^i$< 320
Very high	${\mathit{Er}}^i$≥ 320	Very high	RI ≥ 600