Table 4: Grading standards for enrichment factor (EF; Taylor [25]), geoaccumulation index (Igeo; Muller [11]), contamination factor (Cf; Hakanson [15]) and potential risk index for individual metal (Er; Hakanson [15]).

A. Enrichment factor (EF)
EF ranges Degree of enrichment
<1 No enrichment
1-3 Minor enrichment
3-5 Moderate enrichment
5-10 Moderately severe enrichment
10-25 Severe enrichment
25-50 Very severe enrichment
50 Extremely severe enrichment
B. Geoaccumulation index (Igeo)
Igeo values Igeo Classes Pollution intensity
0 <0 Unpolluted
1 0-1 Unpolluted to moderately polluted
2 1-Feb Moderately polluted
3 2-Mar Moderately to strongly polluted
4 3-Apr Strongly polluted
5 4-May Strongly to very strongly polluted
6 >5 Very strongly polluted
C. Contamination factor (Cf)
Value rangse of Cf Description
Cf< 1 Low contamination factor
1≤ Cf < 3 Moderate contamination factor
3 ≤ Cf < 6 Considerable contamination factor
Cf ≥ 6 Very high contamination factor
D. Potential risk index for individual metal (Er)
≤ Value ranges of Er Description
Er < 40 Low potential ecological risk
40 ≤ Er < 80 Moderate potential ecological risk
80 ≤ Er < 160 Considerable potential ecological risk
160 ≤ Er < 320 High potential ecological risk
Er ≥ 320 Very high potential ecological risk at hand for the substance in question