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Two-hour methyl isocyanate inhalation and 90-day recovery study in B6C3F1 mice
Abstract:
B6C3F1 mice were exposed by inhalation to 0, 3, 10, and 30 ppm methyl isocyanate for 2 hr followed by a 90-day recovery period. Sixteen of eighty (20%) male mice in the 30 ppm group died following exposure. There were no other unscheduled deaths in the mice. Five mice/sex/group were examined at 2 hr or at 1, 3, 7, 14, 28, 49, or 91 days following exposure. Chemical-related changes were restricted to the respiratory system. At 30 ppm there were extensive necrosis and erosion of the respiratory and olfactory epithelium in the nasal cavity. Severe necrosis and epithelial erosion were also found in the trachea and main bronchi. Regeneration of the mucosal epithelium occurred rapidly in the nasal cavity and airways. In the turbinates, mild incomplete olfactory epithelial regeneration persisted to day 91 in the male mice. Intraluminal fibrotic projections covered by respiratory epithelium and bronchial fibrosis were found in the major airways of the 30 ppm male and female mice by day 7. The intraluminal fibrosis persisted to day 91. In males with severe bronchial fibrosis, chronic alveolitis and atelectasis were found. In mice exposed to 3 or 10 ppm, persistent pulmonary changes were not found. These studies indicate that methyl isocyanate inhalation at or near lethal concentrations can cause persistent fibrosis of the major bronchi in mice.
Insights
Methyl isocyanate inhalation caused significant respiratory damage and death in mice at high concentrations. Persistent bronchial fibrosis was observed in survivors, indicating long-term effects of methyl isocyanate exposure.
Area of Science:
- Toxicology
- Respiratory Pathology
- Inhalation Exposure
Background:
- Methyl isocyanate (MIC) is a highly toxic industrial chemical.
- Understanding the long-term respiratory effects of MIC inhalation is crucial for occupational safety.
Purpose of the Study:
- To investigate the toxicological effects and recovery patterns in mice following inhalation exposure to methyl isocyanate.
- To determine the dose-response relationship and identify persistent pathological changes in the respiratory system.
Main Methods:
- B6C3F1 mice were exposed to varying concentrations of methyl isocyanate (0, 3, 10, 30 ppm) via inhalation for 2 hours.
- Animals were observed for mortality and underwent necropsy at multiple time points up to 91 days post-exposure.
- Histopathological examination focused on the respiratory tract, including nasal cavity, trachea, bronchi, and lungs.
Main Results:
- A 20% mortality rate was observed in male mice exposed to 30 ppm methyl isocyanate.
- High-dose exposure (30 ppm) resulted in acute necrosis and erosion of the respiratory and olfactory epithelium.
- Persistent intraluminal bronchial fibrosis and, in males, chronic alveolitis and atelectasis were observed up to 91 days post-exposure.
- Lower concentrations (3 and 10 ppm) did not result in persistent pulmonary changes.
Conclusions:
- Methyl isocyanate inhalation at near-lethal concentrations can induce severe, persistent bronchial fibrosis in mice.
- Rapid regeneration of the respiratory epithelium occurs, but significant fibrosis can remain.
- These findings highlight the potential for long-term respiratory damage from acute, high-level methyl isocyanate exposure.