الفهرس 
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Abstract
This study attempts to summarize information on background levels of metals in soils anthropogenic sources of metals in soil and water systems, critical soil processes which dictate the mobility and bioavailability of metals. Anthropogenic metal inputs are a significant source of metal contamination of soils and waters. In spite of the vital importance of fertilizers and amendments for increased crop production, when used in large amounts they can cause contamination of soils and waters because they contain some undesired impurities such as heavy metals. Metal-containing sewage sludge when applied to agricultural soils can cause contamination of soils, crops, and waters because soil works as a dynamic entity through which metals pass during recycling from the waste to plants, water, or air.
The contribution percentages of the studied factors in the surface layer revealed the order EDTA addition > Ni concentration > applied voltage. In comparison, in the subsurface, third, and bottom layers, the contribution percentages of the three factors showed the order Ni concentration > applied voltage > EDTA addition.
The optimal factors that improved Ni removal from artificially contaminated soils were 10-20 mg kg−1 Ni, 3 V applied voltage, and 0.5-mol EDTA.
The results indicated that the highest removal percentages of heavy metals and other elements from the four soil layers studied follow the order Al (70%) > Co (69%) > Fe (63.5%) > Cu (55%) > Mn (52.8%) > Zn (43.17%) > Cr (41.41%) > Ni (22.26%).