LEVELS OF SELECTED HEAVY METALS IN SOIL AND LEAFY VEGETABLES FROM HIRNA AREAS, ETHIOPIA

Abstract

Leafy Vegetables widely consumed in Hirna, Western Hararghe, Ethiopia such as cabbage (Brassica oleracea var), lettuce ( Lectuca sativa L.) and Swiss chard (Beta vulgaris L.var .cicla) are cultivated on the main roadside soils. For this study, leafy vegetables and soil samples up on which they grow were collected at distances of 5,6 and 7m from the main road and the digestion procedures were optimized with a mixture of conc. 69-72 % HNO3 and 70 % HClO4 for the vegetables samples and a mixture of conc. 69 - 72 % HNO3, 36-38 % HCl and 30 % H2O2 for soil samples and wet digestion procedure was employed to solubilized the metals from the samples. The validation was performed by spiking the samples with a standard solution of each metal having a known concentration and the percentage recovery values in the ranges of 88.6–108.4 % for soil and 87.9 - 98.67 % for vegetable samples. The samples were analyzed with the Flame Atomic Absorption Spectrophotometer (FAAS) to determine level of selected heavy metal (Pb, Cd, Cu, Zn, Ni, Co and Fe) in leafy vegetables and main roadside soils. The results showed that the levels of heavy metal in vegetable samples the ranges of 0.106 - 0.130 mg/L in lead, 1.856- 3.335 mg/L in zinc, 0.902- 1.13 mg/L in copper and 3.409- 5.929 mg/L of iron. The content heavy metal in soil samples also in the ranges of 0.137-0.179 mg/L in lead, 5.61-7.104 mg/L in zinc, 2.360-4.557 mg/L in copper and 7.778- 10.038 mg/L of iron. The levels of cadmium, cobalt and nickel were not detected (ND) in all samples. The heavy metal contents at the same distance from the road were found in leafy vegetables and soil samples in the following order: Fe > Zn > Cu > Pb. All these values were small when compared to the WHO/FAO safe limit, which is an indicated that the leafy vegetables samples in Hirna town area are safe for consumption without the risk of environmental toxicants.