Speciation and mobility study of selected heavy metals in kofe dumpsite soil of jimma town, jimma, Ethiopia

Abstract

Speciation and mobility of selected heavy metals including Cd, Pb and Fe were investigated in Kofe dumpsite soils of Jimma Town, Jimma, Ethiopia. To study vertical mobility of the metals, soil samples were collected at three depth profiles comprising surface soil (0-10 cm), subsoil (20-30 cm), and bottom soil (40-50 cm) using soil auger. Similarly, for horizontal mobility assessment, soilsamples were collected from 5 m, 10 m and 15 m distances starting from the edge of the dumpsite in east, west, north and south directions. Control soil samples were also collected at the same depth profiles, from 200 m away from the dumpsite. The collected samples were air dried, sieved as well as ground before processing utilizing a Community Bureau of Reference (BCR) sequential extraction procedure. The fraction of the target metals in the extracted samples were then determined by flame atomic absorption spectroscopy (FAAS). The mobility factor (%MF) of the target metals was investigated in both vertical and horizontal variations and the obtained results showed that the target metals haveexhibited both vertical and horizontal mobility. The texture, organic matter and pH of thesoil samples were also analyzed for correlation study. Variation among obtained results, i.e., %MF and concentration of analytes, were evaluated using one way ANOVA at (P<0.05). It was observed that Cd and Pb exhibited vertical mobility and thus could lead to pollution of the underground water. Similarly, the highest amount of Pb in the bioavailable fraction may also indicate its horizontal mobility and its high tendency to pollute surface water, sediment as well as agricultural products.