where Cn is the measured concentration of metal n in the sediment and Bn is the geochemical background value of element n in the background sample (Rudnick and Gao, 2003; Yu et al., 2011; Rahman and Ishiga, 2012; Islam et al., 2014). The factor 1.5 is introduced to minimize the possible variations in the background values which may be attributed to lithogenic effects. Geoaccumulation index (Igeo) values were interpreted as: Igeo ≤ 0 – practically uncontaminated; 0 ≤ Igeo ≤ 1 – uncontaminated to moderately contaminated; 1 ≤ Igeo ≤ 2 – moderately contaminated; 2 ≤ Igeo ≤ 3 – moderately to heavily contaminated; 3 ≤ Igeo ≤ 4 – heavily contaminated; 4 ≤ Igeo ≤ 5 – heavily to extremely contaminated; and 5 < Igeo – extremely contaminated.