SEQUENTIAL EXTRACTION OF 9 TRACE-ELEMENTS FROM SLUDGE-AMENDED SOILS

Three separate samples taken from particular location of El-Gabal El-Asfar soils treated with composted sludge and irrigated with liquid sludge effluent were compared with untreated soil. These soils were sampled at 5 depths, i.e. 0-15, 15-30, 30-45, 45-60 and 60-75 cm to estimate the forms of nine trace metals in the solid phase. The soils had been amended with sewage sludge and irrigated with sludge liquids for different periods, i.e. 20, 40 and 60 years. The soil samples were fractionated by sequential extraction to estimate the quantities of these metals in ''exchangeable'', ''sorbed'' ''organic'', ''carbonate'', and ''sulfide'' forms. Data reveal that most of these elements were concentrated (preferential fixation) in the surface layer (0-15 cm), possibly because of the slight decrease in soil apparent density resulting from sludge application. The trace metal contents in exchangeable and sorbed forms of most metals were very low. Sulfide, carbonate and organic forms were shown to be the dominant fractions for most trace metals under study and varied from one element to another. Nevertheless, at least 6 of these metals have a common behaviour. At the longterm addition of sludge application, the predominant metals were: Zn, Fe, Mn, Cr, Ni and Co in sulfide form; Cu in organic form, and Pb and Cd in the carbonate form.