COMPARISON OF THE SENSORY IRRITATION RESPONSE IN MICE TO CHLORINE ANDNITROGEN TRICHLORIDE

The expiratory bradypnoea indicative of upper airway irritation in mic e was evaluated during a 60-min oronasal exposure to increasing concen trations of chlorine and nitrogen trichloride. The airborne concentrat ion resulting in a 50% decrease in the respiratory rate of mice (RD(50 )) was calculated for each chemical. Chlorine and nitrogen trichloride showed dissimilar concentration-response curves. While the maximal re sponse of nitrogen trichloride was reached in 10 min, the maximal resp onse of chlorine was reached between 45 and 60 min of exposure. The re sults showed both chemicals to have an irritant potency of the same or der of magnitude. The RD(50) values of chlorine and nitrogen trichlori de were 3.5 and 2.5 ppm, respectively. On the basis of a TLV-STEL (thr eshold limit value for short-term exposure limit) equal to 0.1 RD(50) and a TLV-TWA (time-weighted average) equal to 0.03 RD(50), the curren t TLVs for chlorine seem too high (1 and 0.5 ppm, respectively) and sh ould be reduced to 0.5 and 0.1 ppm, respectively. For nitrogen trichlo ride, 0.3 ppm and 0.1 ppm are proposed as TLV-STEL and TLV-TWA, respec tively.