Assessment of heavy metals contamination in different crops grown in long-term sewage-irrigated areas of Kolkata, West Bengal, India.

The effects of sewage water on the accumulation of heavy metals (Zn, Cu, Pb, Cd, and Ni) in soils and commonly grown plants were evaluated by monitoring the fields along the water channel running some 30 km eastward of Kolkata, West Bengal, India. The results revealed that the mean Cu, Cd, and Zn contents in sewage water were higher than the recommended level whereas mean concentration of Cd in the irrigated soil is several folds higher than the safe limit. The highest single element pollution index (SEPI) value was found for Cd which ranged from 2.93 to 6.03 with a mean of 5.32 indicating high contamination levels. The value of combined pollution index (CPI) ranged from 1.32 to 1.93 with an average of 1.67 for all the sites indicates that metal concentrations are above the hazard criteria and exhibit multi-element contamination. Furthermore, the results of enrichment factor (EF) indicated that the soils of the study area were highly enriched with metals such as Cd (452.04, extremely high enrichment) followed by Pb (17.32, significant to very high enrichment) > Zn (5.99, significant enrichment) > Cu (3.14, minimal to significant) > Ni (3.07, minimal to moderate). The concentrations of Pb, Cd, and Ni were above the permissible limit in all the crops and Colocasia and Amaranthus accumulate highest metal on the basis of overall metal uptake. The highest mean transfer coefficients (TCs) values for Zn, Cu, Pb, Cd, and Ni were found for cauliflower (0.59), Colocasia (0.67), Amaranthus (0.93), Colocasia (1.02), and Amaranthus (1.09), respectively.