Chronic Inhalation Toxicity of Refractory Ceramic Fibers in Syrian Hamsters

Abstract

This study was initiated to assess the potential for kaolin based refractory ceramic fibers (RCF) to induce toxicity and tumors in Syrian golden hamsters after chronic exposure. To simulate the fiber dimensions found in workplace air and to increase fiber respirability in the rodent, RCF fibers were size-selected before aerosolization to be approximately 1µm in diameter and ~20 µm in length. Three groups of animals were exposed in nose-only inhalation chambers, 6 hrs/day, 5 days/week, for 18 months to 30 mg/m³ of RCF, 10 mg/m³ of chrysotile asbestos (positive control; average diameter = 0.09 µm, average length = 2.2 µm), or to filtered air (negative control). Animals from each group were sacrificed at three month intervals for evaluation of the sequential changes in lung pathology over the course of the study. Microscopic examination of the RCF exposed lungs revealed pulmonary interstitial fibrosis (grade 4 on the Wagner Pathology Grading Scale) starting at 6 months and showed little progression of the lesion through the remainder of the exposure. Examination of the asbestos exposed hamster lungs revealed an average pathology grade of 4.3 at 3 months, which progressed to an average score of 5.0 at 6 months and plateaued at that level. The latter change was characterized by interlobular linking of the lesions observed in the grade 4 lungs. In addition, a time-dependent increase in collagen deposition in the pleura was observed in the RCF exposed animals and to a lesser extent in the positive control animals. RCF exposure resulted in no pulmonary neoplasms. However, pleural mesotheliomas were found in 43 out of 102 RCF exposed hamsters (42%). No lung neoplasms or mesotheliomas were observed in either the chrysotile exposed or negative control hamsters.