Dipartimento di Scienze della Terra and Laboratorio Rettorale Fibre e Particolato Inorganico, Sapienza Università di Roma, P.le A. Moro 5, I-00185, Rome, Italy.
"G. Scansetti" Center for Studies on Asbestos and Other Toxic Particulates and Dipartimento di Chimica, Università di Torino, V. P. Giuria 7, I-10125, Turin, Italy.
J Hazard Mater. 2020 Nov 5;398:123119. doi: 10.1016/j.jhazmat.2020.123119. Epub 2020 Jun 10.
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 oxygen-centred 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 TO 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.
本研究揭示了角闪石石棉在热降解过程中发生的形态和化学结构变化。低铁透闪石和高铁青石棉在室温至 1200°C 的温度范围内加热。加热促进了一系列复杂的铁氧化、迁移和/或聚集过程，最终形成了由新形成的矿物和非晶纳米相组成的脆性纤维假晶。通过定量测定碳中心和氧中心自由基，即羟基（OH）自由基，评估了热改性对毒理学相关石棉反应性的影响。加热不会改变碳自由基，但会极大地影响氧中心自由基的产率。在低温下，两种角闪石的反应性都降低了。在 1200°C 时，透闪石结构发生分解，反应性进一步降低，因为反应性铁离子迁移到新形成的辉石（s）中更稳定的 TO 四面体中。不同的是，青石棉在 1000°C 下的分解导致赤铁矿、富铁辉石、方石英和大量非晶质物质的形成，并恢复了自由基的反应性。我们的发现表明，经过热处理的石棉及其分解产物仍然具有与原始纤维相关的一些毒理学性质。在证明含有热失活石棉的材料是安全的时，石棉惰性化研究除了考虑结晶度外，还应考虑形态和表面反应性。
