Type of Document Master's Thesis Author Hume, Lily Ann URN etd-06082009-171119 Title The dissolution rate of chrysotile Degree Master of Science Department Geology Advisory Committee
Advisor Name Title Rimstidt, james Donald Committee Chair Craig, James R. Committee Member Zelazny, Lucian W. Committee Member Keywords
Date of Defense 1991-05-05 Availability unrestricted AbstractChrysotile can be linked to three diseases: lung cancer, asbestosis, and mesothelioma. The duration and intensity of exposure along with fiber size appear to play an important role in the development of the diseases. Chrysotile is part of the serpentine group which has the general composition of Mg3Si205(OH)4. The fluids in lung tissue contain very low concentrations of magnesium and silicon. As a result they are quite undersaturated with respect to chrysotile and chrysotile will dissolve. Its persistence in lung tissue is simply a result of its dissolution kinetics. The purpose of this study was to estimate the lifetime of a respirable size fiber of chrysotile in lung tissue.
The dissolution reaction for chrysotile for pH's less than nine is: Mg3Si205(OH)4 + 6H+ = 3Mg2+ + 2H4Si04 + H20
This reaction proceeds in two steps. First, the magnesium hydroxide layer of the serpentine dissolves leaving behind the silica structure of the fiber. Then the silica dissolves. Therefore, the fiber lifetime depends upon the rate of silica release. Over the range of undersaturation expected for lung tissue, the rate of silica release was found to be independent of pH with the average rate being 5.94 (±3.05) x 10-10 moles m-2 sec-I. A shrinking fiber model was used to determine the relationship between dissolution time and fiber diameter. It was found that the most hazardous sized fiber of chrysotile (1 μm) would completely dissolve in about 9 months, consideration of one standard deviation above and below the mean of the rate constant gives estimates of the lifetime of a fiber ranging from 6 to 19 months.
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