Masters Theses

Date of Award

12-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Zoology

Major Professor

Gearld L. Vaughan

Committee Members

John R. Kennedy, Jeffery A. MacCabe

Abstract

Occupational exposure to mineral fibers, such as asbestos, has been associated with increased risk of pulmonary fibrosis, malignant mesothelioma and lung carcinoma. It has been proposed that fibers with diameters < 0.25 and lengths > 8 um, possess the greatest capacity for cytotoxicity and cell transformation. (Stanton, 1977). The present study was prompted by the limited data on the health effects of silicon carbide whiskers (SiCW), a recently marketed man-made mineral fibers. This study was designed to compare two SiCW of differing dimensions as well as a non-fibrous form. In order to examine the immediate biological effects of Sic, cultured explants of tracheal epithelium were exposed to a range of fiber concentrations (5 ug/cm2 - 100 ug/cm2) . There were no dramatic effects on ciliary function as measured by optical spectrum analysis which provided discrete ciliary frequencies. Particles were swept by ciliary activity into non-ciliated regions where foci of extensive cell damage and death were observed with whiskers penetrating epithelial layers into the underlying connective tissues. Similiar necrotic foci were observed in tracheas from rats exposed by intratracheal instillation to silicon carbide whisker (SiCW) in vivo. Investigation into the intermediate and long term pulmonary response began with intratracheal administration of SiCW-1 (0.8 um diameter), SiCW-2 (1.5 um diameter), Sic platelets (SiCP), boron carbide fiber (BC) and crocidolite asbestos. By bronchopulmonary lavage, phagocytic cells (macrophages, monocytes, lymphocytes) were harvested for examination of cell population changes. Lavage analysis revealed a significant (p < 0.05) increase in macrophages still in evidence 28 days after SiCW exposure, an early sign of chronic inflammatory processes. Lungs removed from fiber-exposed animals exhibited tissue alterations characterized by severe fibrosis and granulomatous tumors at 18 months post exposure. The highest frequencies of occurence, 88% and 91%, were noted in SiCW-1 treatment groups. Additonal pathological abnormalities included hyperplasia, metaplasia and interstitial pneumonia. Interperitoneal injections of SiCW similarly resulted in inflammatory fibrosis and benign peritoneal tumors. SiCW-1 was shown to produced the greatest cellular damage. The single whisker form of Sic may pose a serious health threat without precautionary handling measures,

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