Fungal strain Aspergillus flavus F3 as a potential candidate for the removal of lead (II) and chromium (VI) from contaminated soil

Abstract

Metal contamination of soil is a serious environmental problem due to mining and use of synthetic products (e.g. pesticides, paints, batteries, and industrial wastes), which are serious threat to human life. The current research is aimed at the remediation of soil contaminated with lead (II) and chromium (VI) using indigenous fungal strains through the comparative study of bioleaching and chemical leaching methods. The removal efficiencies of Pb (II) and Cr (VI) in bioleaching were higher than chemical leaching, where 99% Cr (VI) and 36% Pb (II) were removed by Aspergillus flavus (F3) in bioleaching through the production of approximately 332 mg L-1 malic acid, 213 mg L-1 succinic acid, and 35 mg L-1 citric acid. The removal efficiencies in chemical leaching were 21.30% for Pb (II) and 1.92% for Cr (VI) by malic acid, 29.30% for Pb (II) and 72% for Cr (VI) by succinic acid, 22.21% for Pb (II) and 60.70% for Cr (VI) by citric acid, and 2.20% for Pb (II) and 2.47% for Cr (VI) by oxalic acid. The sequential extraction procedure for Pb (II) and Cr (VI) before and after bioleaching showed that Pb (II) and Cr (VI) mostly bound to stable fractions after bioleaching. Scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX) helped to identify the characteristic changes in the morphology and elemental composition of A. flavus (F3) biomass before and after bioleaching, whereas Fourier transform infrared spectroscopy (FTIR) showed that fungal biomass contain hydroxyl, carboxyl, fatty acids, and amine groups on its surface. The results implied that the fungal strain A. flavus (F3) can be used to remediate soils contaminated with Pb (II) and Cr (VI).