Bioremediation of Lead and Zinc Contaminated Soils by Compost Worm

Background: This study investigated the bioremediation of lead and zinc in contaminated soils by the compost worm Eisenia Fetida. Methods: This experimental study was conducted in vitro using 108 samples. The initial concentrations of 50 and 100 mg/kg for zinc and lead respectively as well as 40 mg/kg and 80 mg/kg for the control group were studied. 30 earthworms were used for bioremediation of 500g samples of the polluted soils during 14 and 28 days. Then, Pb and Zn were measured by atomic absorption kit (Varian 240) in the soil and earthworm’s tissue. Results: The mortality rate of earthworms was insignificant statistically, so that it was lower than 20% when exposed to 86 mg/L of lead. Moreover, the removal efficiency of Pb and Zn was higher than 90% in th soil. Initial concentration of Pb and Zn was 3 and 6 mg/kg and the bioaccumulation was 0.16 and 32 μg/g respectively during 14 days, while they were 0.31 and 59 μg/g at the end of 28 days. The removal efficiency of Pb and Zn was increased as the exposure time and concentration of Pb and Zn in the earthworm bodies increased. Conclusion: As a consequence, the use of earthworms is an appropriate organic and cost-effective method for bioremediation of Pb and Zn significantly. However, the improvement and modification of bioaccumulation in earthworm bodies is an environmental challenge that should be managed.