Concentration of some heavy metals (Cd, Co, Fe & Hg) in soil and edible vegetables in Ogoja urban area of Cross River State, Nigeria

Abstract

The concentration of heavy metals (Cd,Co,Fe & Hg) in soil and some edible vegetables was determined during the rainy and dry seasons of the year, using Atomic Absorption Spectrometer (AAS) after the samples were digested. Forty samples of the eight edible vegetables and forty soil samples, where they were planted, were also collected at the root level of the vegetables. The eight most common edible vegetables considered were Telfairia occidentalis, Amaranthus spp, Corchorus olitorius, Ocimum grattissimum (scent leaf), Solanum melongena (yellow garden egg leaf), Talinum triangulare, Murraya koenigi and Vernonia amygdalina. The result of the analysis revealed that Co and Hg were stringed variables as they were not detected in the soil or vegetables in both seasons of the year. Cd ranged from 0.005-0.043 mgkg^-1 in the soil and 0.005-0.042 mgkg^-1 for rainy and dry season respectively while Fe ranged from (0.015-0.051) mgkg^-1 and (0.019-0.050) mgkg^-1 for rainy and dry season respectively. The mean concentration of Cd accumulated by the vegetable ranged from 0.005-0.010 mgkg^-1 in both seasons, while that of Fe ranged from (0.013-0.034) mgkg^-1 and (0.009-0.033) mgkg^-1 for rainy and dry seasons respectively. From the data, it shows that Fe was more in the soil than Cd, and it was also accumulated by the vegetables more than Cd. The metal’s concentration in the vegetables is still low and  within the permissible limits of FAO/WHO. The amount of metal accumulated is directly proportional to that in the soil. There is no significant difference between the results of the dry and rainy season. There is need to maintain this low level of heavy metals in the soil and vegetables through adequate awareness on the proper disposal of waste and environmental monitoring/evaluation by relevant agencies of the state.

Keywords: Heavy Metals, Concentration, Soil, Edible Vegetables