Chrysotile 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.
next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.
