POTENTIAL TOXICITY OF NONREGULATED ASBESTIFORM MINERALS: BALANGEROITE FROM THE WESTERN ALPS. PART 2: OXIDANT ACTIVITY OF THE FIBERS

Abstract

The asbestiform mineral balangeroite [(Mg,Fe²⁺,Fe³⁺,Mn²⁺)₄₂Si₁₆O₅₄(OH)₃₆], whose toxic potential is unknown, is associated with chrysotile asbestos in the western Alps (Balangero mine, Piedmont, Italy). In order to examine whether such fibers may contribute to the oxidative damage produced by local asbestos dusts when inhaled, balangeroite was studied by means of both cell-free and cellular tests, comparing the results with those concerning the most pathogenic asbestos form, crocidolite. Similarly to the crocidolite surface, iron was mobilized from balangeroite by chelators, to a different extent: deferoxamine > ascorbic acid > ferrozine. Poorly coordinated surface ions, as evaluated from the adsorption of NO as a probe molecule (by both calorimetry and infrared spectroscopy), are even more abundant on balangeroite than on crocidolite. The spin trapping technique shows that surface iron-derived Fenton activity (HO^• from H₂O₂) is similar for the two fiber types, while a pretreatment in ascorbic acid, by reducing previously oxidized surface iron, activates the potential to cleave a C–H bond (yielding CO₂ from formate anion). Balangeroite, like crocidolite, produces nitrite accumulation, lipid peroxidation, and NO synthase activation in a human lung epithelial cell line (A549). All these findings, regarded as features related to the toxic potential of asbestos, suggest that balangeroite may be a potentially hazardous fiber per se and could be partly responsible for lung diseases reported in epidemiological studies in exposed miners.

The research has been carried out with the financial support of Regione Piemonte, Assessorato all’ Ambiente, as part of a muldisciplinary project, entitled “Asbestos Hazard in the Western Alps.” Elena Gazzano, Chiara Groppo, and Francesco Turci are recipients of a doctoral fellowship and Maura Tomatis of a postdoctoral fellowship from Regione Piemonte in the framework of the project.