Heavy Metals in Wetland Soil of Greater Dhaka District, Bangladesh

The current paper determines heavy metals in sediments of six freshwater wetlands of greater Dhaka district from November 1999 to September 2000. The sampling took place in summer, rainy season, and winter, wherein for each season five soil samples were collected from the wetland at a depth of 0 – 15 cm. To assess the status of heavy metal pollution in the sediments, geo-accumulation factor (Igeo), contamination factor (CF), degree of contamination (Cd), and enrichment factor (EF) have been evaluated, with the concentrations of Cd, Mn, Ni, Zn, Cu, Fe, and Pb in the sediments ranging within 0.005 – 0.055 mg/kg, 35.0 – 275.04 mg/kg, 0.35 – 2.19 mg/kg, 0.77 – 12.54 mg/kg, 4.11 – 19.17 mg/kg, 115.60 – 955.94 mg/kg, and 1.82 – 3.93 mg/kg, respectively, standing in the following order: Fe > Mn > Cu > Zn > Pb > Ni > Cd. The maximum concentrations of Mn, Ni, and Pb belonged  to summer. Significant temporal variation was observed only in case of Cd, whereas concentrations of Cd, Fe, and Mn varied spatially. The Igeo for Mn indicates a strongly to extremely polluted condition in wetlands, whereas that of Ni and Pb show moderately polluted condition, and for Zn and Cu, it suggests moderately to strongly polluted conditions. The CF values for heavy metals in sediment have been below 1, indicating low contamination. In addition, Cd < 6 indicates low degree of heavy metal contamination. The EF for heavy metals in wetland sediments are in the following order: Cu>Mn>Pb>Cd>Zn>Ni, suggesting that the sediments very highly rich in Cu, while Mn, Pb, and Cd exhibit significant enrichment. In the studied wetlands the EF for Zn and Ni shows moderate and deficiency to minimal enrichment, respectively. Implications of these findings can be used as baseline information to monitor and assess the degree of sediment pollution in lentic wetlands.