INHALATION TOXICOLOGY: IX. TIMES-TO-INCAPACITATION FOR RATS EXPOSED TO CARBON MONOXIDE ALONE, TO HYDROGEN CYANIDE ALONE, AND TO MIXTURES OF CARBON MONOXIDE AND HYDROGEN CYANIDE

Laboratory rats were exposed to experimental atmospheres that contained: (a) carbon monoxide (CO) in air; (b) hydrogen cyanide (HCN) in air; and (c) mixtures of CO and HCN in air. The toxic potency of each of the three types of environments was evaluated toxicokinetically by measurement of time-to-incapacitation as a function of the toxic gas concentrations. Regression equations were derived that describe those relationships for exposure to CO or HCN alone. Analysis of the data from the combined-gas exposures, and comparison of that data with the results obtained from the exposures to each gas alone, lead to the conclusion that the toxicity of the combination is definitely greater than would be produced by either gas alone. There was, however, no evidence for a synergistic action--in which the effect of the combination would have been greater than that predicted from the sum of the two individual effects. An empirical equation was derived that allows calculation of a predicted time-to-incapacitation for any combination of CO and HCN concentrations that are within the ranges utilized in the experimental exposures.