Biological Immobilization of lead from lead sulphide by Aspergillus Niger and Serpula Himantioides

The abilities of Aspergillus niger and Serpula himantioides to immobilize lead (Pb) from lead sulphide (PbS) were investigated. Upon growth on potato dextrose agar (PDA) amended with PbS which contained 10mM Pb, no visible solubilization activity was detected. A. niger produced biomass in greater quantity compared to S. himantiodes in both experimental and control media. With a ratio of 1.13, A. niger growth was stimulated on PbS-amended media while that of S. himantiodes, with a growth ratio of 0.46 was inhibited. Despite its smaller biomass, S. himantiodes accumulated over five times more Pb than A. niger with 85.7 ± 4.9 µmol of Pb per g of dry weight while A. niger contained 14.6 ± 1.3 µmol of Pb per g of its dry weight. Both fungi immobilized Pb through the formation of crystalline precipitates and energy dispersive x-ray analysis revealed the precipitates to be Pb containing. This transformation is of importance in the weathering of metal- bearing rocks as mineral neogenesis.