Concentration-time-response relationship under conditions of single inhalation of carbon tetrachloride

Abstract An attempt was made to establish a concentration-time-response relationship for a single inhalation of CCl 4 in rats. Rats were exposed to CCl 4 under conditions of various combinations of concentration ( C = 1350, 2500, 3400, 5200, and 6900 ppm) and time ( t = 1, 2, 3, and 6 hr). As a parameter of toxicity, glutamic-oxaloacetic transaminase (GOT) activity was measured. The concentration-time-response relationship obtained by graphic analysis of the data could be described by the equation: log g = nC m log t + γC + log δ , where g is the GOT activity 24 hr after the end of exposure, and n , m , γ, and δ are empirical parameters. It was found from this relationship that concentration has more influence on toxic effect than time does. The concentration-time relationship, furthermore, suggested that the time-weighted average of the concentration of CCl 4 (and presumably also other atmospheric contaminants), which can be applied only under the condition of C × t = constant, does not correctly reflect the “toxicity value” of exposures. Quantitative expression of the concentration-time-response relationship makes it possible to predict the “no observable effect level” (NOEL) of CCl 4 for various exposure times.