Fungal bioweathering of mimetite and a general geomycological model for lead apatite mineral biotransformations

Fungi play important roles in biogeochemical processes such as organic matter decomposition, bioweathering of minerals and rocks, and metal transformations, and therefore influence elemental cycles for essential and potentially-toxic elements, e.g. P, S, Pb, and As. Arsenic is a potentially-toxic metalloid for most organisms, and naturally occurs in trace quantities in soil, rocks, water, air and living organisms. Among more than 300 arsenic minerals occurring in nature, mimetite [Pb5(AsO4)3Cl] is the most stable lead arsenate and holds considerable promise in metal stabilization for in situ and ex situ sequestration and remediation through precipitation, as do other insoluble lead apatites, such as pyromorphite [Pb5(PO4)3Cl] and vanadinite [Pb5(VO4)3Cl]. Despite the insolubility of mimetite, the organic acid-producing soil fungus Aspergillus niger was able to solubilize mimetite with simultaneous precipitation of lead oxalate as a new mycogenic biomineral. Since fungal biotransformation of both pyromorphite and vanadinite have been previously documented a new biogeochemical model for the biogenic transformation of lead apatites (mimetite, pyromorphite and vanadinite) by fungi is hypothesised in this study by application of geochemical modelling together with experimental data. These models should allow for accurate prediction of fungal dissolution patterns of lead apatites based on based on pH, cation-anion composition and concentrations, and other parameters. A general pattern for fungal biotransformation of lead apatite minerals is proposed, proving new understanding of ecological implications of the biogeochemical cycling of component elements as well as industrial applications in metal stabilization, bioremediation and biorecovery.