Assessment of heavy metal contamination and risk evaluation from selected plants in Funtua, North Western Nigeria

Abstract

Contamination of plants (Abelmoschus esculentus (Okro), Allium cepa (onion), Amaranthus viridis, Spinacia oleracea (Spinach), Brassica Oleracea (Cabbage), Digitaria horizontalis, Commelina diffusa) by copper (Cu), cobalt (Co), nickel (Ni), lead (Pb) and chromium (Cr), and the subsequent human exposure risks, were determined in Funtua region, where wastewater from Funtua textile is used for irrigation. The concentrations of heavy metals (mg/kg fresh wt.) in plant samples ranged from 106.45 to 230.55 for Cu, 602.75 to 1121.50 for Cr, 70.50 to 145.10 for Ni, Below Detection Limit (BDL) to 2.15 for Pb and BDL for Co. Thus, the concentrations were found to be above the WHO (1996) permissible limit with exception to Co and Pb in all plant samples. The levels of the heavy metals analysed in the plant samples were in the following trend: Spinacia oleracea>Allium cepa>Amaranthus viridis>Abelmoschus esculentus >commelina diffusa> Brassica Oleracea >digitaria horizontalis. Hazard Index 1.01 × 105 and 4.20 × 104 were obtained for children and adults, respectively. Estimated daily intakes in mg/day ranged from 3.07 × 10-3 to 7.16 × 10-3 for Pb, 2.63 × 10-1 to 6.13 × 10-1 for Cu, 1.63 × 10-1 to 3.80 × 10-1 for Ni, 0.12 × 101 to 0.29 × 101 for Cr and BDL for Co in adult and children, respectively. Cu, Ni, Cr and Pb intake rates were above recommended minimum risk levels (MRLs) in both children and adult in all the plants, while Co poses no risk in all the plant samples. The result obtained from subjecting the data to statistical analysis revealed that there was no significant difference in the levels of the analysed plant samples at p ≥ 0.05 across the sampling sites.