effect of kiwi shell and incubation time on mobility of lead and cadmium in contaminated clay soil

in this study, the effectiveness of kiwi shell was investigated to reduce the mobility of lead and cadmium in clay soil in different intervals. for this purpose a clay soil sample was contaminated with lead and cadmium in distinct dishes with 10 and 600 ppm concentrations respectively and mixed with 5% kiwi shell. samples were placed in incubator, and then sampling of soil in incubator was performed in intervals 3 hours, 1, 3, 7, 14, 21 and 28 days. heavy metals concentrations were determined in different fractions of soil including exchangeable, carbonate, fe-mn oxides, organic matter, and residual with sequential extraction procedure and atomic absorption spectrophotometry. the results showed that during incubation, lead concentration in treatments with kiwi shell rather than control soil increased in carbonate from 19.48 to 26.18 and in organic matter from 9.06 to 18.66 percent. exchangeable, fe-mn oxides and residual fractions decreased from 11.48 to 6.69, 45.72 to 39.83 and 14.21 to 7.90 percent respectively. in samples with absorbent compared with control soil, cadmium concentration in carbonate and organic matter increased from 28.20 to 38.40 and 18.76 to 24.72, while in exchangeable, fe-mn oxides and residual decreased from 16.66 to 13.69, 37.25 to 19.65 and 6.24 to 3.61 percent respectively. this study revealed that kiwi shell function in decreasing cadmium and lead mobility in studied clay soil were increased with increasing incubation time, but cadmium compared with lead required additional time to transfer and mobility to constant and stable soil fractions such as, organic matter and fe-mn oxides.