Ricerc@Sapienza

This study discloses the morphological and chemical-structural modifications that occur during thermal degradation of
amphibole asbestos. Low-iron tremolite and iron-rich crocidolite were heated at temperatures ranging from r.t. to
1200 °C. Heating promoted a complex sequence of iron oxidation, migration and/or clustering and, finally, the formation
of brittle fibrous pseudomorphs consisting of newly formed minerals and amorphous nanophases. The effects
of the thermal modifications on toxicologically relevant asbestos reactivity were evaluated by quantifying carbon- and
oxygen-centred, namely hydroxyl (°OH), radicals. Heating did not alter carbon radicals, but largely affected oxygencentred
radical yields. At low temperature, reactivity of both amphiboles decreased. At 1200 °C, tremolite structural
breakdown was achieved and the reactivity was further reduced by migration of reactive iron ions into the more stable
TO4 tetrahedra of the newly formed pyroxene(s). Differently, crocidolite breakdown at 1000 °C induced the formation
of hematite, Fe-rich pyroxene, cristobalite, and abundant amorphous material and restored radical reactivity. Our
finding suggests that thermally treated asbestos and its breakdown products still share some toxicologically relevant
properties with pristine fibre. Asbestos inertization studies should consider morphology and surface reactivity, beyond
crystallinity, when proving that a thermally inactivated asbestos-containing material is safe.