Soils can naturally reduce mobility and bioavailability of heavy metals
as they are retained in soil by sorption, precipitation and complexation
reactions. These natural processes can be accelerated by addition of some soil
amendments, which converting the soluble forms to more geochemical stable
solid phases. Hence, the current study represents a trial towards ameliorating
soils polluted with heavy metals resulted from some anthropogenic activity.
To achieve this target, in situ an incubation experiment was executed on two
soil samples taken from El-Gabal El-Asfar farm (Qalubia Governorate) and
El-Saff (Giza Governorate), subjected to heavy metals pollution due to
irrigating with sewage effluent and industrial wastes, respectively. The studied
two soils were mixed thoroughly in pots of 200 g soil capacity with some soil
amendments, i.e., poultry manure, organic compost and bentonite at a rate of 2
%, then the pots were daily wetted wit distilled water to reach a constant
moisture content (field capacity) and incubated under room temperature at
different periods of 0, 25, 50 and 75 days.
Soil samples were taken to identify the effective role of the applied soil
amendments throughout the different incubation periods, however, the values
of EDTA-extractable Ni, Co and Cd were determined. The most important
obtained results could be summarized in the following:
1. EDTA-extractable amounts of Ni, Co and Cd showed a progressively
decreased in both amended soils with poultry manure, with a more effective
role by increasing time of incubation period. The removed amounts of the
studied metals for both investigated soils followed the descending order: Ni >
Co > Cd. Also, the removal capacity of poultry manure seemed a highest
figure with Ni, lowest with Co and intermediate with Cd.
2. Application of organic compost led to minimize the value of EDTAextractable Ni, Co and Cd in both soils under study. The adsorbed amounts of
these metals in El-Gabal El-Asfar soil exceeded obviously the corresponding
ones in El-Saff soil. This trend was emphasized by the removal capacity of the
compost for Ni, Co and Cd, which was recorded higher values in El-Gabal ElAsfar soil than in El-Saff one.
3. Values of EDTA–extractable Ni, Co and Cd from both the bentonite amended
soils also showed progressively decreased with increasing the incubation
period. The absolute adsorbed amounts of Ni were the highest, whereas those
of Co and Cd were the lowest and intermediate, respectively, in the bentonite
amended soils. In general, the removal capacity of bentonite for Ni was higher
than Co and Cd over the studied incubation periods. It is noticed that the
removal capacity of bentonite for Co was almost similar over all the
incubation periods.