A study of the effect of chrysotile fiber surface composition on genotoxicity in vitro

Chrysotile fibers (NIEHS intermediate length) were treated with ultrapure H Cl to alter the fiber surface chemistry without substantially changing fibe r morphology or dimensions. The objective of the study Mas to determine whe ther fiber surface chemistry is an important variable in fiber genotoxicity in vitro. The modified fibers, along with native chrysotile fibers, were u sed to challenge Chinese hamster lung fibroblasts (V79) in vitro using the micronucleus induction genotoxicity assay. Fiber dimensions were assessed u sing scanning electron microscopy by measuring the distribution of fiber le ngths in 3 length ranges. less than 3 mu m, 3-10 mu m, and greater than 10 mu m. For both treated and native fiber samples, 500 fibers were examined. Results indicate that acid-treated fibers were about 20% shorter than untre ated chrysotile. Surface chemistry alterations were verified by zeta-potent ial reversal, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM-EDS) elemental analys is. Scanning Auger spectrometry indicated the presence of Mg, O, and Si in both treated and native chrysotile samples, which confirmed the surface pur ity of both fiber samples. Both XPS and SEM-EDS analysis demonstrated subst antial depletion of Mg from fiber surfaces. Results of the micronucleus ass ay showed a positive concentration-related response for both samples, with toxicity evident only at the highest concentration. No significant differen ce was found for the treated and untreated chrysotile samples. These result s indicate that the surface chemistry is not an important variable in the i n vitro genotoxicity of chrysotile asbestos in V79 cells as detected by the micronucleus assay under the conditions used in this study, and support a model of chemically nonspecific chromosomal and spindle damage effects.