DISTRIBUTION OF HEAVY METALS IN BIO-INDICATORS, SOILS, AND VEGETABLES OF SELECTED COMMERCIAL COCOA FARMS IN ONDO STATE, NIGERIA.

Abstract

The distribution of heavy metals Cr, Cu, Fe, Mn, Ni and Pb in the three selected cocoa farm in Ondo State, Nigeria, was evaluated during the two major seasons in Nigeria. This was done to determine the level of heavy metals in soil, the farm river, the bio- indicators (crab and earthworm) and the flora part (worowo (Senecio biafrae), Xanthosoma species (koko-posho) and fern) of each of the farm. The samples were collected during 2012/2013 rainy season (April - October) and dry season (November - January). The samples were analyzed after digestion for heavy metal concentrations and their variability for both wet and dry seasons. The heavy metal concentrations were determined using Atomic Absorption Spectrophotometer (AAS). The results of analyses show the mean values as follows: Cd, Pb, Ni,Fe, Cu and Mn 0.6 mg/kg, 1.43 mg/kg, 10.07 mg/kg, 200.03 mg/kg, 31.39 mg/kg, 33.03 mg/kg respectively, for crab samples obtained from the three farm during dry season, while during the rainy season Cd 1.83 mg/kg, Pb 2.89 mg/kg, Ni 1.99 mg/kg, Fe 64.60 mg/kg, Cu 19.92 mg/kg, Mn 11.99 mg/kg. For soil samples from the three farms during the dry season Fe, Cu, Mn had 54.03 mg/kg, 36.00 mg/kg and 29.60 mg/kg respectively, while Pb, Cd, Ni had 1.5 mg/kg, 1.8 mg/kg, and 9.80 mg/kg respectively. During the rainy season Fe, Cu, Mn had 60.01 mg/kg, 26.03 mg/kg, 21.01 mg/kg respectively for the fauna part of the farm, while during the dry season, Fe, Cu, Mn had (7.02 - 45.03 mg/kg), (10.04 - 45.03 mg/kg) and 1.20 - 30.63 mg/kg respectively. For efo worowo (Senecio biafrae), samples obtained from the three farms during the dry seasons Cd, Pb Ni had (0.01 - 1.20 mg/kg), (0.91 - 1.69 mg/kg) , (0.03 - 0.20 mg/kg) and Fe, Cu, Mn (4.00 - 30.09 mg/kg), (1.20 - 32.39 mg/kg), (1.21 - 21.00 mg/kg) respectively, but during the rainy season, Cd, Pb, Ni has (0.01 - 0.40 mg/kg), (0.01 - 2.89 mg/kg), (0.01 - 1.20 mg/kg) while Fe, Cu, Mn (5.46 - 26.00 mg/kg), (3.00 - 19.12 mg/kg), (2.89 - 11.99 mg/kg) respectively. The concentration of the heavy metals exceeded the WHO (2002) and FPA (1991) recommended limit for safe water, aquatic food and agricultural soil. The results confirmed that the three farms were highly polluted and the concentrated metals have exceeded the recommended maximum limits set by the Canadium standard 2002 for safe water, aquatic food and agricultural soil in Canada.