Abstract

This study was conducted to determine the heavy metals concentration in soil and Amaranthus retroflexus grown on irrigated farmlands along the Makera Drain, Kaduna, Nigeria. The objectives were mainly to detect the presence of heavy metals in soil and vegetable grown in the study area, compare seasonal variation in concentration of metals, identify the transfer factors for heavy metals,  compare the concentration of heavy metals in soil and vegetable in sample and control site, compare the concentration of heavy metals in soil/bioaccumulation in vegetable in sample site and control site in relation to the permissible limits specified by WHO/FAO, NAFDAC, FEPA and E.U Standards. Samples of soil and Amaranthus retroflexus were collected in the rainy and dry season for the year 2013 from upstream and downstream portion of the Sample site and control site.  Analysis for the concentration of these heavy metals; Cu, Cr, Cd, Fe, Pb and Zn was conducted by the use of AAS (by Atomic Absorption Spectrometry) method. The transfer factor was identified and determined by the use of the formular TF=Mp/Ms. The difference between concentrations of heavy metals in portions of drain, seasons and sites was done by the use of T-test statistical analysis. Results from this study indicate that concentration value of Cr and Fe in the soil samples were generally higher than the FEPA maximum permissive limits while the concentrations of Pb (0.87-1.41), Cd (0.0014-8.02), Cu (13.21-14.25), and Zn (10.10-112.04 in soil samples were generally lower than the maximum permissive limits (Pb; 1.6, Zn; 300-400; Cu; 70-80mg/kg), except for samples from control site. On the other hand, in vegetables, the mean concentrations of  Cd (0.013-2.12), Cr (0.058-2.80) and Fe (331.6-1252) in sample site were higher than the WHO/FAO maximum permissive limits (Cd - 0.2, Cr - 1.3, Fe - 425mg/kg), while in control site vegetables, concentration for all heavy metals was found below the maximum permissive limit. Furthermore, the study revealed that some areas of the sample site were more polluted by a particular metal than the other due to the prevailing anthropogenic activities in the area, and that all areas of the site run the risk of pollution by Cd, Cr and Fe in vegetables.

Key words: Amaranthus retroflexus, Makera Drain, soil/bioaccumulation, transfer factors, vegetable.