FUNGI-INDUCED CHEMICAL WEATHERING OF ASBESTIFORM CHRYSOTILE

Fungal bioleaching has been shown to be an important mechanism for chemical weathering of minerals, particularly in soils. Chrysotile, an asbestiform mineral used for industrial purposes, is common in serpentine-bearing rock formations and soils. Weathering of chrysotile can potentially promote CO₂ sequestration via mineral carbonation. In contrast, this process can also result in the release of asbestiform fibers which represent a major respiratory hazard. One proposed asbestos remediation method is bioleaching by fungi that break down asbestiform serpentine minerals in the process of extracting iron as a micronutrient. Currently, however, the mechanisms, mineral alteration products, and geochemical impacts of fungi-induced weathering of chrysotile remains unclear. This study uses batch culture experiments to (1) determine if Talaromyces sp., a fungal strain isolated from serpentine soils in China (Li, Z., et al., 2015), is capable of breaking down the structure of chrysotile in vitro, (2) compare the bioleaching effect of Talaromyces sp. on chrysotile when bioavailable iron is present or absent in the culture medium, (3) compare the effect of pH on the in vitro dissolution of chrysotile under biological and abiotic conditions.

Over the course of 18 days, Talaromyces sp. was grown in the presence of asbestiform chrysotile (NMNH #91261) in Czapek media containing MES buffer (pH 5.5), half with and half without FeSO₄. Because the pH dropped to ~4.5 during fungal growth, an abiotic experiment was performed to mimic the change in solution pH with time by adding 2M HCl. Samples were measured for magnesium and silicon concentrations and pH, and growth in culture flasks was visually tracked and photographed. Regardless of the supply of bioavailable iron, chemical weathering rates of chrysotile were nearly identical whether dissolution was biologically or abiotically driven. This indicates that dissolution is promoted by acidity, rather than direct biological mechanisms, and that Talaromyces sp. was responsible for chrysotile weathering only through the production of organic acids. Furthermore, XRD and SEM analysis of chrysotile fibers showed no structural changes, indicating that Talaromyces sp. may not have any direct potential applications for bioremediation of chrysotile asbestos.