Potential of different crop species for nickel and cadmium phytoremediation in peri-urban areas of Varanasi district (India) with more than twenty years of wastewater irrigation history

Heavy metals introduced into soil by indiscriminate dumping along with irrigating with sewage effluent often lead to toxic accumulation of heavy metal ions, which not only impair soil productivity but also cause health hazards by entering into food chain via soil-plant-animal-atmosphere continuum. To evaluate the potential of different crop species for nickel (Ni) and cadmium (Cd) phytoremediation, fifteen crop species comprising of cereals, vegetables and flowers were collected from differentially contaminated soils (DTPA-Cd 5.7-6.75 mg kg(-1), DTPA-Ni 16.50-20.85 mg kg(-1)). The tissue metal concentration and relative efficiency of transfer of heavy metals from soil to plant (transfer factor) for various groups of crops were worked out. The uptake of Cd and Ni increased with contents in soils and the major part of taken up Cd and Ni is translocated to the floricultural crops with maximum accumulation occurred in roots. Values of translocation factor of Cd and Ni were ranged between 0.2 to 0.8 and 0.2 to 1.0 respectively for the different crops studied. The mean total root colonization by arbuscular mycorrhiza in these soils ranged from 15% for cauliflower to 76% for marigold, suggesting a certain adaptation of these indigenous to such environmental stress. Among the different crops studied marigold with highest translocation factor, mycorrhization and Cd and Ni content in root part holds considered as a potential economic crop for phytoremediation.