Role of iron in the reactivity of mineral fibers.

Any foreign body containing iron may be (or become) highly toxic in vivo. If its solubility in water is poor, surface chemistry governs the reactivity at the solid-liquid interface. Iron toxicity thus increases with the extent of exposed surface. Iron of endogenous origin may also be deposited on the particle surface and be activated under particular circumstances. The chemical processes that implicate surface iron as a primary cause of toxicity are: free radical release, mobilization by chelators, iron-catalyzed reactions. Three kinds of solids are compared: (i) well-known toxic materials, for example asbestos; (ii) non-toxic iron oxides; and (iii) model solids with surface exposed iron prepared for investigations on the reactivity of iron in biological media. The iron content of the solid is not directly related to the biological response: only a small fraction of ions, in a well-defined coordination and redox state, appears involved in the toxicity of the mineral dust.