Role of time as a factor in the toxicity of chemical compounds in intermittent and continuous exposures. Part II. Effects of intermittent exposure.

Abstract

Because of fluctuations in levels of industrial air pollution linked to weather and other factors, a joint U.S.‐Soviet research team studied differences in the effect of time in exposures of air‐breathing animals to controlled varied concentrations of air pollutants. An experimental model environment was used to investigate the effects of nitrogen dixoide (NO2), sulfur dioxide (SO2), and benzene (C6H6) in the air environment of laboratory animals, with both continuous and intermittent exposures. For intermittent exposures the investigators used amounts of toxic gases whose cumulative total equaled the total in the continuous exposures, and intercalated the intermittent exposures with periods of nonpolluted air. To equal the cumulative total concentration of the single continuous exposures over an equal time period, the concentrations of toxic gases were necessarily greater in the intermittent exposures. Part I of this work deals with the effects of continuous exposure to C6 H6 on the central nervous system and blood. Toxic effects of continuous exposure to various concentrations of C6H6 were found involving the central nervous system and blood. The time‐effect relationships could be approximated on a log‐log scale by straight lines. Similar results were obtained with SO2. Using different parameters to measure toxicity, similar results were obtained with NO2 —namely, concentration‐time relationships that when plotted on a log‐log scale gave straight lines. Part II concerns the toxicities of Intermittent exposures to C 6 H 6 and NO2; three parameters were used. The toxic effects of NO2 with intermittent exposure were not reduced as was the case with C6H6. Data are presented to show that intermittent exposure to NO2 may be more toxic than continuous exposure when short‐term peaks of NO2 concentrations are involved.