The effect of incubation time and silk worm cocoon on mobility of zinc and copper in contaminated clay soil

Of the problematic agents in the ecosystem, heavy metals have special importance because they are unabsorbable and have physiologic effects on living beings at low concentrations. This study has investigated the effect of silk worm cocoon on reducing mobility of zinc (Zn) and copper (Cu) for the first time. To this end, 5% cocoon adsorbent was added to the studied soil, which had been contaminated with Cu and Zn in separate containers at concentration of 600 mg/l. The experiment was performed in three repeats and two treatments (with and without adsorbent). Samples were incubated at 28°C at constant humidity for 3 hours, 1, 3, 7, 14, 21, and 28 days. Then both treatments were extracted using sequential extraction method and the concentration of Zn and Cu was processed using atomic absorption spectrophotometry. The results showed that there were changes in mobility of the Zn and Cu added to soil; adding silk worm cocoon to soil increased organic phase of Zn and Cu as compared to the soil without adsorbent. Data were analyzed by SPSS software. All comparisons of the means were performed at statistical level of 5% using Student’s independent t-test. Student’s independent t-test showed that the highest significant difference (P < 0.05) was observed in the organic fraction of the Cu-Zn contaminated soil with cocoon, as compared with the Cu-Zn contaminated soil without cocoon.