Chemical Characterization and Reactivity of Iron Chelator-Treated Amphibole Asbestos

Abstract

Iron in amphibole asbestos is implicated in the pathogenicity of inhaled fibers. Evidence includes the observation that iron chelators can suppress fiber-induced tissue damage. This is believed to occur via the diminished production of fiber-associated reactive oxygen species. The purpose of this study was to explore possible mechanisms for the reduction of fiber toxicity by iron chelator treatments. We studied changes in the amount and the oxidation states of bulk and surface iron in crocidolite and amosite asbestos that were treated with iron-chelating desferrioxamine, ferrozine, sodium ascorbate, and phosphate buffer solutions. The results have been compared with the ability of the fibers to produce free radicals and decompose hydrogen peroxide in a cell-free system in vitro. We found that chelators can affect the amount of iron at the surface of the asbestos fibers and its valence, and that they can modify the chemical reactivity of these surfaces. However, we found no obvious or direct correlations between fiber reactivity and the amount of iron removed, the amount of iron at the fiber surface, or the oxidation state of surface iron. Our results suggest that surface Fe3+ ions may play a role in fiber-related carboxylate radical formation, and that desferrioxamine and phosphate groups detected at treated fiber surfaces may play a role in diminishing and enhancing, respectively, fiber redox activity. It is proposed that iron mobility in the silicate structure may play a larger role in the chemical reactivity of asbestos than previously assumed.

Inorganic Materials and Living Organisms: Surface Modifications and Fungal Responses to Various Asbestos Forms

“…[8,9,19] Iron chelators reduce free radical release from asbestos, [5,14] although no direct correlation may be established between the amount of iron removal and the reactivity at the fiber surface, which depends not only on the amount of surface iron but also on its coordination and oxidation state and on the fiber micromorphology. [15,27,32,33] The incubation with F. oxysporum, similarly to the treatment with chelators, causes a decrement in HOC release, with some differences among the different asbestos types examined. In the case of crocidolite and chrysotile, iron removal by the fungus fully blunted HOC radical activity.…”

“…[5,11,12] These reactions initiate or contribute to the overall pathogenicity. [13,14] Incubation of the fibers with an aqueous solution of some chelators was reported to inhibit surface reactivity [15] and to decrease DNA damage and lipid peroxidation in vitro. [16][17][18] Synthetic chrysotile with no iron in the structure was recently reported not to be cytotoxic toward human epithelial cells in a culture.…”

A Biomimetic Approach to the Chemical Inactivation of Chrysotile Fibres by Lichen Metabolites

“…A similar chelating and masking synergic action was previously reported for des-A C H T U N G T R E N N U N G ferrioxamine and ferrozine on crocidolite asbestos. [12,67] In some pioneering studies, leached chrysotile exhibited a reduced cytotoxicity [63] and a decreased potential to induce mesothelioma in rats. [68] Such effects were ascribed to the chelator-driven rupture of the crystalline framework and its whole conversion into the debris of amorphous silica.…”

Free radical generation in the toxicity of inhaled mineral particles: the role of iron speciation at the surface of asbestos and silica

“…Crocidolite, Na 2 (MgFe 2+ ) 3 Fe 3+ 2 Si 8 O 22 (OH) 2 , UICC (Union Internationale Contre le Cancer), SSA BET =8 m 2 g -1 , was from the same batch used previously. 16,24,30 Min-U-Sil quartz (MIN) was from US Silica (SSA BET = 5.2 m 2 g -1 , iron content 0.075% as Fe 2 O 3 ); a pure quartz dust (QA), previously employed for research on surface bound radicals, 31 was obtained from quartz chips purified by melting (99.999% SiO 2 , Atomergic) and ground in an agate mortar, SSA BET = 4.5 m 2 g -1 .…”