Surface reactivity of amphibole asbestos. A comparison between two tremolite samples with different surface area

Surface reactivity of a fibrous tremolite sample from Castelluccio Superiore (Italy) was investigated by means of free radical generation following incubation in H2O2solution buffered at pH 7.4, for several time points, ranging from 1 day to 1 month. Results obtained were compared with those of another fibrous tremolite sample (from Maryland, USA), with much smaller surface area. Structural, morphological, and chemical alterations induced on tremolite by incubation were investigated by HR-TEM/EDS. The generation of HO•and COO-•radicals following reaction of tremolite with H2O2or formate ion was investigated by spin trapping/EPR spectroscopy. The dissolution process and surface modification were slower for the Maryland sample, with lowest surface area. Surface modification indicated the occurrence of either low- or high-coordinated Fe centres on the surface, as well as the evolution of their nuclearity. In turn, iron centres determine the reactivity of the fibre surface and the yield of HO•and COO-•radical species. The evolution of radical reactivity over time was proved to be largely dependent on surface area, with the highest radical yield occurring for low-area tremolite incubated over long times. The experimental results obtained in this study as well as the comparison with previous studies further confirm that surface reactivity of mineral fibres and inorganic particles is not dependent on Fetotcontent per se, but is likely due to surface properties and occurrence of specific iron sites.