The Effect of Diatomite and Incubation Time on Distribution of Chemical Forms of Lead in Calcareous Contaminated Soils

The presence of heavy metals in water and soil are major concern for the environment due to their toxicity to many life forms. Stabilization of heavy metals in remediation of contaminated soils is one of the cost-effectiveness and rapid implementation method. In order to study the effect of diatomite on chemical forms of Lead in calcareous soils, a factorial experiment was conducted in a completely randomized design (CRD) with three levels of diatomite application in soil (0, 2 and 5 % by weight), four levels of incubation time (1, 2, 4 and 8 weeks) and in twocontaminated soils with three replications. Chemical distribution of Lead in soils were determined using Tessier sequential extraction method during the mentioned incubation times and reduced partition index (IR) and mobility factor (MF) of the metals were calculated as a Lead mobility indices in the soils. The obtained results showed that the application of diatomite significantly (p ≤ 0.01) decreases the lead in the exchangeable and carbonate fractions and increases it in the iron and manganese oxide, organic and residual bond fractions significantly in comparison to the control treatment. The IR and pH values increased but MF and DTPA-extractable Lead values decreased with increasing diatomite level and incubation time which demonstrates a decrease in the mobility of lead in the soils. Lead mobility reduction in the clay loam soil compared to the one in the sandy loam soil was probably due to higher content of clay and lower content of Calcium Carbonate Equilibrium.  Generally, itcan be concluded that the addition of diatomite into the soil especially with high levels (5%) reduces the bioavailability and mobility of the Lead in the soil.