Effect of soil amendments and crop varieties on the amelioration of heavy metal uptake into crops grown on polluted soils of Bangladesh

Bangladesh possesses many industrial sites, whereby wastes and effluents are directly discharged into the environment without any treatment. Agricultural areas are contaminated thereby and the food quality is impaired. Therefore, the aim of the present work was to develop simple and cost effective strategies to reduce soil-plant transfer of harmful substances. Three sites were selected in the vicinity of Dhaka city (Tongi pharmaceutical, Tejgaon industrial and Hazaribagh tannery area). Field and pot experiments were carried out with different varieties of field crops (rice, wheat and tomato) and different soil amendments (cowdung, city waste compost, oil cake, waterhyacinth, poultry litter, lime and red mud). At the site Tongi, pollutants mainly consists of organic compounds. The soil of Tejgaon is acidic (pH=5.7), contains high organic matter and elevated concentrations of Zn (685 mg/kg), Pb (136 mg/kg), and Cd (2.6 mg/kg). The Hazaribagh region is polluted by a highly elevated concentration of heavy metals, especially Cr (11000 mg/kg). The amendment by organic residues significantly improved harvested rice yield as well as the contents of heavy metals were partly reduced on Tongi soil. The different varieties of rice and wheat showed distinct differences in biomass yield and in heavy metal accumulation on three soils. The positive effect of lime application in reducing metal uptake by rice, wheat and tomato plants were observed on both Tejgaon and Hazaribagh soil, compared to the control. Red mud (ferric oxide) applied in small amounts, on Tejgaon and Hazaribagh soil, led to an increase in biomass production and improved yield for rice plants and to significant reductions of soil plant transfer for Zn, Ni, Cd and Cr. (author)