Time Effect on Distribution of Different Fractions of Lead in Polluted Soils

Adding heavy metals to soils leads to change of their original distribution pattern. Heavy metals distribution in soils depends upon heavy metal، application level، application time and soil characteristics as well. This investigation was conducted to assess the time effect on distribution of different fractions of Lead in soils. The experiment conducted as a factorial in a completely randomized design with three replications and two levels of cow manure (0 and 5%) and two levels of Lead using Lead nitrate (0 and 200 mg kg-1). Samples were incubated at 250C and 60% of field capacity for 120 days with different time intervals (0-30، 0-60، 0-90 and 0-120 day) to determine Lead fractions using sequential extraction methods. The results showed that Lead concentration decrease in exchangeable، carbonated and residual fractions during the time. Also the interactions between cow manure and time cause of decreases in the exchangeable and residual fractions and increases in the carbonated، Fe-Mn oxides-bound as well as organic matter-bond fractions. The interactions between time and Lead concentration lead to decrease in the exchangeable، carbonated and residual fractions and increase in the Fe-Mn oxides-bound and organic matter-bond Lead fractions. Since the most availability and toxic potential of lead is in the exchangeable-solution، the advantage of the this study is to reduce potion of this section during the time.