Lead Biosorption and Biosynthesis of Lead Nanoparticles by Bacillus Tropicus Isolated from Soils Containing Electronic Wastes in Isfahan

Electronic wastes are the remnants of electronic devices buried in the soil without processing and contain toxic substances such as heavy metals. Lead is one of the heavy metals in many electronic goods that, if not properly processed, can cause toxicity in the soil and may harm living things in very low concentrations. Therefore, the aim of the present study was to investigate the biosorption of lead metal by Bacillus tropicus isolated from soils containing electronic wastes in Isfahan.

In this cross-sectional study, sampling of contaminated soils in several areas of the Zainal Pass hills of Isfahan, which is the landfill of electronic wastes, was performed. After measuring the temperature, pH, TOC, and the amount of metals in the soil sample, lead-resistant bacteria were isolated. The growth rate of bacteria was evaluated at concentrations of 5 to 35 mM of lead. Then, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined. The morphology, antibiogram, and molecular identification of the bacteria were performed by colony-polymerase chain reaction method and bioabsorption of bacteria was evaluated by ICP-OES. Finally, XRD, SEM images, and EDS were evaluated to investigate the fabrication of lead nanoparticles. The raw data were analyzed by SPSS software, using an independent t-test.

Based on the findings of this study, the pH of the evaluated soil was 9.4, its temperature was 27.8 ° C, the TOC of the sample was 1.8%, and the amount of soil lead was measured at 658.4 ppm based on ICP-OES analysis. It was significantly higher than normal. The lead-resistant bacterial strain isolated to lead had 99/69% genetic affinity with Bacillus tropicus, which had a high biological removal potential (56.35%) of lead metal.  The XRD, SEM, and EDS results showed the conversion of adsorbed lead metal to nanoparticles.

Considering that Bacillus tropicus showed high resistance and adsorption to lead metal, it can be a suitable option for the bio-removal of lead from electronic and other industrial wastes in the future after the removal of antibiotic resistance genes.