Concentration of Selected Heavy Metals in Soil and Edible Vegetables in Obanliku Urban Area of Cross River State, Nigeria

Abstract

The soil and edible vegetable samples were collected from Obanliku Urban Area of Cross River State and were digested and analyzed for the cadmium (Cd), chromium (Cr), iron (Fe) and mercury (Hg) (heavy metals) concentration using Flame Atomic Absorption Spectrometer (AAS) in Chemistry Laboratory, University of Calabar. The eight vegetables were considered such as Amaranthus spp., Corchorus olitorius, Murraya koenigii, Ocimum grattissimum, Solanum melongena, Talinum triangulare, Telfaira occidentalis and Vernonia amygdalina. The results revealed that the mean concentration of the metals in the soil in mgkg-1 ranged from (0.003-0.017) and (0.003-0.015) for Cd, (0.005-0.040) and (0.004-0.038) for Cr, and (0.052-1.541) and (0.050-1.511) for Fe in rainy and dry seasons respectively. Also, the mean concentration of the metals accumulated by the vegetables in mgkg-1 ranged from (0.002-0.010) for Cd, (0.003-0.018) and (0.003-0.016) for Cr, and (0.013-0.175) and (0.013-0.150) for Fe in rainy and dry season respectively. The concentration of Hg was not detected in the soil or vegetables. The mean concentration accumulated by the vegetables and that present in the soil was in the order: Fe > Cr > Cd > Hg. These results showed that there is no significant difference between the amount of metals in the soil or that accumulated by the vegetables in rainy and dry seasons of the year. Also the amount of metals accumulated by most of the vegetables was directly proportional to the amount present in the soil where they are planted. The bioaccumulation ratios and Target Hazard Quotients (THQ) were all less than 1. The results indicate that the concentration of Cd, Cr, Fe & Hg in the soil and vegetables were still low and within the permissible limits of WHO/FAO. Thus, the consumption of the vegetables in the area at the time when this study was carried out may not pose any health risk.