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

An attempt was made to establish a concentration-time-response relationship for a single inhalation of CCl4 in rats. Rats were exposed to CCl4 under conditions of various combinations of concentration (C = 1350, 2500, 3400, 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 = nCmlog t + gamma C + log delta, where g is the GOT activity 24 hr after the end of exposure, and n, m, gamma, and delta 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 CCl4 (and presumably also other atmospheric contaminants), which can be applied only under the condition of C X 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 CCl4 for various exposure times.