Table 6 Degree of contamination for particular heavy metals and the corresponding evaluation standards for potential ecological risk

\(C^{i}_{f}\)

<1, non-contamination

≥ 1 < 2, light

≥2, <3, moderate

≥3, heavy

C _d

<8, low

≥ 8 < 16, moderate

≥ 16 < 32, relatively high

≥32, very high

\(E^{i}_{r}\)

<40, low

≥ 40 < 80, moderate

≥ 80 < 100, strong

≥320, extremely high

RI

<150, low

≥ 150 < 300, moderate

≥ 300 < 600, strong

≥600, very strong