Synergistic Effects of Nitrogen Dioxide and Carbon Dioxide Following Acute Inhalation Exposures in Rats

摘要

All fires occurring in air produce carbon dioxide (CO2). Fire involving nitrogen-containing products will also generate nitrogen dioxide (NO2), a pulmonary irritant. In Fischer 344 male rats, the LC50 (30 minute exposure plus 14 day post-exposure observation period) for NO2 was 200 ppm (with 95% confidence limits of 43 to 51%); whereas, the LC50 for NO2 in the presence of 5% CO2 was 90 ppm (with 90% confidence limits ranging from 70-120 ppm). Exposure to NO2 increased the methemoglobin (MetHb) levels in the arterial blood. At the end of the 30 minute exposures, the MetHb levels were 2-3 times higher in the animals exposed to the combination of NO2 (200 ppm) and CO2 (5%) than in those exposed to NO2 only. Deaths from NO2 were all post-exposure and occurred earlier in the presence of NO2 plus 5% CO2 than in the absence of the CO2. The time of death was concentration-dependent when both gases were present. At death, evidence of hemorrage and extensive edema was observed in the lungs. The mean lung wet weight/body weight ratio from rats exposed to 200 ppm NO2 with and without 5% CO2 was 3-4 times that of non-exposed rats. More edema was noted with NO2 and CO2 than with NO2 alone.