Transformation and Stabilization of Lead and Chromium Using Aspergillus sp. and Bio-charcoal Amendment

The threat of heavy metals such as Cr and Pb is already known; they have serious negative effects on animal and human health and also persist for a long time in the environment, which is the reason they are frequently detected in soil and water and efforts are made to convert them to nontoxic forms and stabilize them. The current study aimed at finding an efficient organism with high transforming capability of Cr and Pb and well surviving ability to get back into the soil further, and adding biochar to stabilize the transformed metals. The current study first dealt with Cr and Pb transformation by Aspergillus sp. in different concentrations and further applied to contaminated soil to treat contaminant, next untransformed metal from the soil was stabilized by bio-charcol amendment provided from Pistia stratiotes leaves. The obtained results demonstrated that Aspergillus sp. could transform 96% of Cr and Pb at 40 mg/L. At 80 and 100 mg/L, transformation was up to 87.22% and 74.87% for Cr and 76.52% and 68.12% for Pb by forming well biomass in malt extract medium. Further application to soil containing 20 and 40 mg/kg of Cr and Pb respectively, Aspergillus sp. minimized significant quantities of both metals in the exchangeable fraction; at 20 mg/kg there was almost no available form of metals, but at 40 mg/kg there was about 5 mg/kg of Cr and about 3 mg/kg of Pb, but in the control, exchangeable form contained almost the same concentration about 17 mg/kg and 38.6 mg/kg of Cr and 18.6 mg/kg and 38.3 mg/kg of Pb were found. Further biochar was applied to Aspergillus sp. treated soil and great impact was observed on the stabilization of metals and it also reduced the exchangeable fraction of metals. Based on the obtained results, it can be concluded that the strains used in the current study efficiently transformed the metals and biochar successfully stabilized metal at greater extent in the soil. Therefore, it is suggested as a considerably important factor to treat metal contaminated sites in the environment.