Comparative study of bioavailability and transfer of heavy metals from irrigation water and soil to Amaranthus spp. vegetables

Abstract

The present investigation was on the assessment of concentrations of different heavy metals in irrigation water, agricultural soil and vegetables (Amaranthus spp.) grown on the University of Ilorin Teaching and Research Farm. The possible health hazard to humans through food chain transfer was discussed. Irrigation water, soil and Amaranthus spp. were analyzed for Cr, Co, Ni, Cu, Pb, Cd, Mn, Fe and Zn concentrations. Transfer factors (TF), daily intake rate (DIR) and target hazard quotient (THQ) for daily consumption of 0.345kg of the plant were evaluated using the data obtained from the analysis.   The concentration of these metals in the soil were as follows; Mn (76.5 – 225.5 mg/kg), Fe (2063.5 – 8697.0 mg/kg), Zn (9.0 – 25.5 mg/kg), Cu (2.0 – 8.0 mg/kg), Cr (<0.1 – 8.5 mg/kg), Pb (<0.1 – 33.0 mg/kg), while Ni, Co and Cd were not detected (<0.1 mg/kg). Only Mn, Fe, Cu and Zn were detected in the irrigation water and in the plant wereMn (0.41 mg/L), Fe (0.30 mg/L), Cu (0.02 mg/L), Zn (0.02 mg/L) and Mn (390 – 940 mg/kg), Fe (405 – 662.5 mg/kg), Cu (0.00 – 10.0 mg/kg), Zn (50.0 – 110.0 mg/kg) respectively. The TF was in the order Zn >Mn> Cu > Fe, while the DIR were below the tolerable limits and the THQ were in the ranges Zn (1.0510^-3 –2.3110^-3), Mn (1.7210^-2 –4.1410^-2), Fe (3.5610^-3 –5.8310^-3) and Cu (1.1310^-3 –1.5010^-3). The results also showed that the levels of Zn, Fe and Mn in the vegetables were higher than the international standards and the calculated THQs implied that these concentrations would have no adverse effect on the consumers over the period of time. However, the concentrations of the heavy metals need regular monitoring to prevent excessive build-up over time in the vegetable.

Keywords:  Heavy metals, irrigation water, Bioavalaibilty, Amaranthus spp, health hazard