Delayed effects of NO2 exposure on alveolar permeability and glutathione peroxidase in healthy humans.

Potential toxic effects of prolonged NO2 exposure below the current threshold limit value (TLV) were examined in 14 healthy, nonsmoking adults. The subjects were exposed to 2.3 ppm NO2 and to clean air for 5 h with a 1-wk interval between exposures. Physiologic and biochemical measurements were obtained during the exposures and until 24 h after. A 14% decrease in serum glutathione peroxidase activity (GSH-Px) was observed 24 h after the start of the NO2 exposure, while indications of a 22% decrease in alveolar permeability were found 11 h after the start. There were no indications of mucous membrane irritation or of decreased lung function during or after NO2 exposures. The results support the assumption that a delayed response is a feature of the human reaction to NO2 even below the current TLV of 3 ppm, and they stress the importance of an extended period of observation in future NO2 exposure studies.