LEVELS OF SELECTED HEAVY METALS IN CEREALS PRODUCED AROUND CHIRO TOWN, WESTERN HARARGHE

Abstract

The concentrations of heavy metals (Mn, Cr, Pb, Fe and Cd) in different varieties of maize and sorghum samples were determined by using flame atomic absorption spectrometry. Dry ashing method was used to destroy the organic matter to determine the concentration of five heavy metals. A wet digestion procedure, using mixtures of HNO3 and HCl was optimized for the decomposition of powdered maize and sorghum samples.The accuracy of the method was checked by the spike method. The quantities of the analyzed heavy metals were found in the range 1.76-2.25 for Fe, 1.21-2.55 for Cd, 2.81-4.10 for Mn, 1.38- 1.26 for Cr and 0.12-1.68 for Pb in the sorghum varieties and 1.89 -2.02 for Fe, 1.30-3.41 for Cd, 2.61-3.01 for Mn, 2.30- 2.68 for Cr and 0.12-1.45 for Pb for maize varieties in mg/kg. The results were compared with values reported by FAO/WHO limit. The concentrations of lead obtained in the varieties of maize including sample code 2 (Efato), 3 (Shumbure) and 4 (Bukuri) and in the varieties of sorghum 5 (Abdalota), 6 (Muyira) and 7 (Wachila) were greater than the recommended limit by FAO/WHO. Similar results were also obtained for cadmium in the two cereals. The other two samples from maize and sorghum, 1(Shashamane) and 8 (Shafare), respectively, showed concentrations of both Pb and Cd lower than the recommended limit by FAO/WHO. The mean concentrations of heavy metals in varieties of maize and sorghum were found to be in thefollowing order. For (Fe): 5 > 3 > 1⋍2 > 4 > 6 > 7 >5, for Cd: 3 > 8 > 7 > 6 > 1 > 2 > 4 > 5, For Mn: 6 > 8 > 7 > 3 > 5 > 2 ⋍ 1 > 4 , for Cr: 1> 3 > 5 > 4 > 6 > 7 > 2 > 8 and for Pb: 5 > 4 > 3 > 2 > 6 > 7 > 1 > 8. There was no significant difference (p < 0.05) between varieties 1 and 2 of maize in the iron and manganese concentrations. Based on the findings of the study, it is possible to conclude that the levels of some heavy metals determined in the analyzed cereal samples were greater than the permissible limits set by FAO/ WHO, hence are not safe and need proper consecration.