Assessment of toxicological indices of some heavy metals in soil, cabbage and lettuce samples grown along some rivers in Kano State, Nigeria

Abstract

Three samples of soil, lettuce and cabbage were collected from three sites along River Jakara (Zungeru, Airport Road and P.R.P) and River Getsi (Gama, Gayawa and Getsi) and were analyzed for Fe, Pb, Zn, Cu, Mn, Cr, As, Ni, Cd, Co, and Hg content using Atomic Absorption Spectrophotometer and the toxicological indices of the soils and vegetables were determined. The metal content of the soil exceeded the FAO/WHO approved limits in irrigation soil. Pb and As exceeded the approved limit in all the vegetables and levels of Zn, Cr and Cd in the lettuce collected from sites along River Getsi exceeded the approved limits by FAO/WHO as the irrigation area were dotted with leather, paint, foam and chemical industries coupled with the activities of auto mechanics, furniture and wood processing companies. It was found that lettuce accumulated more toxic metals of Pb, Cr, As, and Cd than cabbage with values ranging from 0.59 – 3.48, 0.2 – 0.4, 2.2 -5.0 and 0.6 – 3.12mg/Kg respectively. The soil Pollution Load Index (PLI) in all the sites was found to be above 1 while the Degree of Contamination (Cd) was found to be from highly to extremely contaminated soils with the lowest Cd of 2.67 found in Gama while the highest was 5.35 in Getsi site. The Geometrical Index (Igeo) ranged from 0.07 in samples from P.R.P to 1.17 in samples collected from Zungeru suggesting an uncontaminated to moderately contaminated soils. The Bioaccumulation factor showed highest transfer of Fe and Zn in both cabbage and lettuce and most metals have Transfer Coefficient value above 1 suggesting excessive transfer. Based, on the above findings, Government at all levels should initiate policies that will mitigate the effects of heavy metals in the study area.