Lichen deterioration of asbestos and asbestiform minerals of serpentinite rocks in Western Alps

Naturally Occurring Asbestos (NOA) on serpentinite outcrops are exposed to abiotic and biotic environmental forces which may affect their toxicity-relevant properties. Lichen colonization and deterioration were examined on monomineralic and polymineralic veins, containing asbestos (chrysotile, tremolite) and/or asbestiform minerals (antigorite, balangeroite, carlosturanite, diopside). The hyphal penetration of Candelariella vitellina within the different veins ranged from few hundreds of microns to several millimetres. The various NOA mineral species contacted by lichen hyphae were differently modified in their chemical composition. NOA were incubated in the laboratory with oxalic acid to mimic the dissolution process driven by lichen metabolites bearing acidic and chelating functions, typically pulvinic acid in the case of C. vitellina. The incubated fibres were chemically modified to the same extent of those colonized by C. vitellina in the field and were used to examine the effects of lichen deterioration on the toxicity-relevant release of Reactive Oxygen Species (ROS). Incongruent dissolution patterns observed in the cases of chrysotile-, chrysotile + balangeroite- and tremolite bearing veins were associated to a significant (even if not complete) inactivation of the surface. Conversely, the veins bearing minerals subjected to congruent dissolution (antigorite, diopside) maintained their reactivity. Lichen colonization may thus be associated to a bioattenuation process on some kinds of fibrous veins, but such effect cannot be generalized to all colonized NOA.