ESR and Mössbauer studies on detoxified crocidolite: Mechanism of reduced toxicity

A process for the detoxification of crocidolite fibers was previously reported in the literature. The fibers of this mineral asbestiform were treated with ferric oxide salts to form a metal-micelle polymer surface coating which prevented physiological reactions with the mineral. In the present study, detoxified crocidolite was tested for its ability to generate hydroxyl radicals in the presence of hydrogen peroxide; the intensity of the electron spin resonance signal was less than that produced by the native toxic crocidolite fibers. Similar experiments showed that the ability of the detoxified crocidolite to reduce oxygen was also decreased compared with the native crocidolite. The availability of ferrous iron present in the two crocidolite fibers to catalyze the above reactions was investigated with the chelating agent ferrozine. The results indicate that ferrozine was able to mobilize fewer ferrous ions from detoxified crocidolite compared with the native crocidolite. Moreover, Mössbauer-effect spectroscopy studies have shown that the detoxification process results in both bulk and surface changes of the crystal-chemistry of the detoxified sample. This detoxification process also introduces a surface coating comprising ferric ions which shield near-surface ferrous irons and consequently reduces the Fenton-type reactivity of the fibers. It is therefore inferred from this combination of techniques that the ability of the crocidolite fibers to generate oxygen-centered radicals is dependent on the iron redox state and its chelation to different molecules. This in turn, may have an important effect on the ability of the fibers to exert their toxicity.