Lead bioimmobilization in contaminated mine soil by Aspergillus niger SANRU

Lead (Pb) contamination in soils is becoming one of the most serious environmental issues in recent years. For this reason, amendment induced immobilization of Pb in contaminated soils has been considered as an eco-friendly and cost-effective technique to minimize soil Pb availability. This study aims at evaluating efficacy of the newly discovered Aspergillus niger strain, SANRU in bioimmobilization of Pb in contaminated mine soil. To conduct bioimmobilization, phosphate rock (PR) at various P/Pb ratios of 0 (T₁), 2 (T₂), 4 (T₃), or 6 (T₄) molars was inoculated with the A. niger strain SANRU and subsequently introduced into the soil. The soil sample inoculated with A. niger SANRU and P/Pb molarity ratio of 0 (T₁) in this study showed the highest Pb bioimmobilization efficiency, as well as a significant reduction up to 65 % in the unimmobilized Pb concentration and an increase in residual Pb fraction. Our in-depth Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) studies revealed that the successful Pb bioimmobilization in this sample was attributed to Pb oxalate formation in the soil. In T₂ treated soil with A. niger and P/Pb molarity ratio of 2, the Pb oxalate was precipitated solely as Pb minerals in spite of the presence of available phosphate. In the samples with A. niger and higher amounts of PR (T₃ and T₄) the Pb bioimmobilization efficiency was significantly lower than T₁ but hydroxypyromorphite was formed in these samples. Our data thus propose that A. niger SANRU alone suffice to bioimmobilize Pb in contaminated soil.