Grade	Element Potential Ecological Risk Index		Comprehensive potential ecological risk index
Grade	Risk index	Risk level	Risk index	Risk level
1	$E_{r}^{i} < 40$	Low	$R I < 150$	Low
2	$40 \leq E_{r}^{i} < 80$	Medium	$150 \leq R I < 300$	Medium
3	$80 \leq E_{r}^{i} < 160$	Higher	$300 \leq R I < 600$	High
4	$160 \leq E_{r}^{i} < 320$	High	$R I \geq 600$	Extremely high
5	$E_{r}^{i} > 320$	Extremely high	-	-