ASBESTIFORM RIEBECKITE (CROCIDOLITE) DISSOLUTION IN THE PRESENCE OF FE CHELATORS - IMPLICATIONS FOR MINERAL-INDUCED DISEASE

X-ray photoelectron spectroscopy (XPS) and solution chemistry were use d to monitor the changes in surface composition of crocidolite fibers in a 50 mM NaCl solution at pH = 7.5 and 22 degrees C in the presence of several Fe chelators(citrate, EDTA, or desferrioxamine) for up to 3 0 d. The data show that the introduction of Fe chelators dramatically increases the rate at which Fe is released from the surface in compari son with a control group to which no chelators were added. In particul ar, XPS shows that Fe3+ is more effectively removed in the presence of the chelators even though it is highly insoluble in aqueous solutions at near neutral pH. This suggests that Fe chelators can alter the dis solution mechanism of amphiboles from the process that dominates in Na Cl solutions. This change in dissolution mechanism (particularly the e nhanced rate of Fe release) is an important consideration for models o f mineral-induced pathogenesis that rely on oxidation and reduction pr ocesses. Efforts were made to estimate the Fe-release lifetimes of cro cidolite fibers under the conditions of our experiments to guide the a ssessment of the biodurability of these fibers in human lung tissue. O ur results suggest that crocidolite fibers may persist for several yea rs, releasing Fe to lung fluids during this time. This estimated lifet ime is longer than that previously estimated for chrysotile fibers and is consistent with the lifetimes previously observed in asbestos mine ral lung-burden studies.