Abstract
The present study was designed to investigate the detrimental effects of toxic metals on agricultural practices carried out with polluted river water from one of the most polluted rivers, the Turag in Dhaka city, Bangladesh. Toxic metal concentrations in irrigation water, soil and rice grains (Oryza sativa) were measured from three different sites near the river. Bioaccumulation factors (BAF) were calculated to recognize the transfer of toxic metals from the soil to rice grains. The estimated daily intake (EDI), target hazard quotient (THQ), total target hazard quotient (TTHQ) and the target carcinogenic risk (TR) were calculated to evaluate the health risks. All values from these three sites were compared to the values obtained from a nearby site where irrigation was carried out with bore-well water. The mean concentrations of Zn, As, Cu, Ni, Pb and Cr in rice grains were 1.71 ± 0.52, 2.20 ± 0.84, 1.47 ± 0.17, 1.27 ± 0.10, 1.98 ± 0.21 and 0.21 ± 0.09 ppm, respectively, indicating that the concentrations of As and Pb were much higher. For all sites, THQ values for As and Pb were higher than 1.0 indicating that consumption of such rice will have a long-term, harmful effect on consumers. Furthermore, the TR values for As and Pb were higher than the threshold level (10−6), implying that the lifetime cancer risk is increased for residents eating this rice. Toxic metals intrude into the river water as well as the bore-well water. Rice cultivated at all sites is thus burdened with toxic metals that make it unsafe for human consumption.