Inorganic Materials and Living Organisms: Surface Modifications and Fungal Responses to Various Asbestos Forms

Abstract

In a previous study several strains of soil fungi were reported to remove iron in vitro from crocidolite asbestos, a process that was envisaged as a possible bioremediation route for asbestos-polluted soils. Here, we get some new insight into the chemical basis of the fiber/fungi interaction by comparing the action of the most active fungal strain Fusarium oxysporum on three kind of asbestos fibers--chrysotile, amosite, and crocidolite--and on a surface-modified crocidolite. None of the fibers examined significantly inhibited biomass production. Even the smallest fibrils were visibly removed from the supernatant following adhesion to fungal hyphae. F. oxysporum, through release of chelators, extracted iron from all fibers; the higher the amount of iron at the exposed surface, the larger the amount removed, that is, crocidolite > amosite >> chrysotile. When considering the fraction of total iron extracted, however, the ranking was chrysotile > crocidolite > amosite > heated crocidolite, because of the different accessibility of the chelators to the metal ions in the crystal structure. Chrysotile was the easiest to deplete of its metal content. Iron removal fully blunted HO* radical release from crocidolite and chrysotile but only partially from amosite. The removal, in a long-term experiment, of more iron than is expected to be at the surface suggests a diffusion of ions from the bulk solid towards the surface depleted of iron by fungal activity. Thus, if the fibers could be treated with a continuous source of chelators, iron extraction would proceed up to a full inactivation of free radical release. The fungal metabolic response of F. oxysporum grown in the presence of chrysotile, amosite and crocidolite revealed that new extracellular proteins are induced--including manganese-superoxide dismutase, the typical antioxidant defense--and others are repressed, upon direct contact with the fibers. The protein profile induced by heated crocidolite was different, a result suggesting a key role for the state of the fiber/hyphae interface in protein induction.

Lichens on asbestos–cement roofs: Bioweathering and biocovering effects

“…Chemical modifications in crocidolite were not previously detected in crocidolite fibres inhaled by rats after 365 days [49]. By contrast, a significant release of Fe in culturing solutions was detected when fibres were incubated with soil fungi in laboratory experiments, thus suggesting an iron extraction due to siderophore-like molecules or acidic metabolites [50][51][52]. The depletion of Na, which occupies exposed sites along the 110 mineral cleavage plain [53], and the trend towards a decrease in the FeO tot content which are determined by Acarospora may follow a similar mechanism driven by lichen metabolites.…”

“…Moreover, lichens, by physically contacting the fibres, chemically modify their composition. Laboratory experiments showed that modifications in the chemical composition of chrysotile and crocidolite, similar to those we detected below lichens on asbestos-cement, affect their surface chemistry, determining a decrease of their Fenton activity [24,27,51,52], i.e. one of the main factors currently related to asbestos toxicity [5,6,37].…”

A Biomimetic Approach to the Chemical Inactivation of Chrysotile Fibres by Lichen Metabolites

“…[13] In this context, soil fungi have recently been reported by some of us to modify the chemical composition of asbestos fibres. [16][17][18][19] The symbiotic lichen-forming fungi are well-known physical and chemical weathering agents of natural and artificial mineral substrata. [20,21] Besides the physical effects related to the penetration of fungal hyphae, lichens chemically deteriorate minerals by secreting a wide range of primary and secondary metabolites.…”

Bacterial Weathering of Asbestos

“…Release of siderophores by some fungal species [1,12] was effective in reducing cytotoxicity of chrysotile asbestos in in vitro conditions. The damaging effect on naked DNA in in vitro situations was reduced by removal of iron from asbestos, by fungi belonging to Verticillium species, Paecilomyces species and Fusarium oysporium [4].…”

“…Its low cost has further made its applicability extensive, ever since the industrial revolution. Found mainly in serpentine [1] and amphibole rocks [2], it is categorized into six types based on the chemical composition. They are chrysotile (white asbestos), crocidolite (blue asbestos), amosite (brown asbestos), tremolite, anthophyllite and actinolite.…”