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EC number: 201-145-4 | CAS number: 78-81-9
The expiratory bradypnoea indicative of upper airway irritation was evaluated in mice during 15 minutes oronasal exposure to incresing concentrations of the test substance. The airborne concentration resulting in a 50% decrease in the respiratory rate of mice (RD50) was calculated for each test compound. The test substance was as well tested for pulmonary toxicity in mice and for the effects of a 120-min exposure on the respiratory rates of non-anaesthetized, tracheally cannulated mice (RD50TC).
An RD50 value of 91 ppm and a RD50TC value of 406 ppm were measured respectively. The test substance has a low irritant potency.
Previous studies with several chemicals have shown that the RD50 can be used successfully to predict safe industrial exposure. At 0.1 RD50, humans would experience some light disconfort and this should be the highest level permitted in industry. At 0.01 RD50, no sensory irritation is observed and a convenient threshold limit value (TLV) would be 0.3 RD50 (the midpoint on a logarithmic scale between the 0.1 and 0.01 RD50). The predicted safe levels to prevent upper airway irritation should not exceed 10 ppm for the test substance.
To determine RD50TC value, much higher concentrations of the test substance has to be used. According to the authors, it is not linked to the anaesthesia. The main difference between RD50 and RD50TC indicate that the test substance is mainly irritant of upper airways.
Moreover, while the respiratory rate responses of oronasally exposed mice indicative of nasal irritation set in rapidly and were reversible when exposure to the irritants ceased, the respiratory rate responses of cannulated mice were slower to develop than in oronasally exposed mice, and no, or cincomplete, revocery was observed agter the end of exposure, when mice were allowed to breath fresh air. This phenomenon might be caused by effects on the lower airways, culminating in pulmonary congestion.
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