The Lung: A Reaction Chamber for Asbestiform Minerals

University Of Idaho, Moscow ID

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Abstract

DESCRIPTION (provided by applicant): The health risks posed by mineral dusts have earned a great deal of attention in the past decade with the emerging problems from Libby, Montana and from several Canadian asbestos mines. Tremolite asbestos specifically has been named as a culprit in causing rare lung diseases in exposed humans. The proposed project intends to comprehensively study the behavior of tremolite under simulated lung conditions. Moreover, conversions of minerals occur in many low-temperature environments (e.g., soils), and we are interested in researching possible mineral transformations in the lungs. Studies report finding significant and carcinogenic amounts of tremolite asbestos in lungs, without fmding similar amounts of this asbestos in the material to which workers were exposed. Interestingly, Case (1991) reviews a study by J. C. Wagner (1987) in which no evidence of tremolite was found in initial and "respirable" asbestos fibers, however, tremolite was "clearly evident in the lungs of the rats after three months of exposure." This phenomenon has been attributed mainly to tremolite biodurability. However, our theoretical calculations (Gunter and Wood, 2000, and this proposal) show that, under conditions similar to those found in the lungs, less harmful chrysotile asbestos might convert to more harmful tremolite asbestos. The specific goals of this project are to study the kinetic aspects and mineralogical characteristics of tremolite dissolution and the proposed chrysotile/tremolite conversion. To our knowledge, no kinetic data on the dissolution of tremolite under lung conditions exist. We will look for evidence of the conversion of chrysotile to tremolite in single fiber and bulk asbestos laboratory experiments designed to mimic conditions of the lungs. For example, chrysotile fibers will be placed in solutions containing lung-like concentrations of Ca2+, Mg2+, Fe2+, etc. at 37 C, pH = 4-7 and shaken over various lengths of time. The final compositions of the solutions will be analyzed using ICP-AES and ion chromatography. Initial and final characteristics of the fibers and other minerals possibly formed from the experiments will be carefully detailed with a number of resources: atomic force microscopy, scanning- and transmission- electron microscopy, powder and single crystal x-ray diffraction and possibly x-ray fluorescence for the bulk samples. To our knowledge, this is the first time the idea of mineral conversion in the lung has been suggested as an explanation of the discrepancy between natural tremolite concentrations and tremolite concentrations in the lungs. Even if this particular reaction is kinetically unfavorable, this project lays the groundwork for future studies of mineral reactions in the lungs.