INFLUENCE OF SOIL TYPE DIFFERENCES ON THE DISTRIBUTION OF DTPA EXTRACTABLE HEAVY METALS IN SOILS IRRIGATED WITH INDUSTRIAL EFFLUENTS

Abstract

This study determined the effects of the application of industrial liquid waste from a textile factory on the distribution of DTPA extractable metals in a Pelli-Eutric Vertisol and an Eutric Fluvisol at Akaki in Ethiopia, classified according to the FAO-UNESCO Soil Classification System. The Fluvisol is slightly basic on the surface and has sandy clay to clay loam texture, while the Vertisol is strongly basic on the surface, and has clayey texture throughout the profile. Application of the industrial liquid waste modified and increased levels of DTPA metals in the treated Akaki soils compared to natural levels in the background soils. The Fluvisol has more DTPA extractable Fe, Mn, and Zn than the Vertisol. Surface Cu, Cd and Ni contents are higher in the Vertisol opposed to the Fluvisol. However, there is more enrichment of these metals within depth, in the Fluvisol. Pb concentrations in the Fluvisol are about twice as much as the Vertisol throughout the profile. Soil solution pH seems to have the greatest influence for most metals. Surface Cu and Ni of the treated Vertisol are more influenced by organic matter, while on the whole CEC has negative influence on metal availability because of competing ions. These metals generally decrease consistently with depth in the Vertisol, while in the Fluvisol the profile distribution is irregular. Leaching due to coarser textural composition and floodplain soil impacted by the contaminated river sediments are responsible for metal redistribution in the Fluvisol than in the Vertisol. There is thus greater risk of metal uptake by vegetables on the Fluvisol than the Vertisol.