Acute toxicity of high concentrations of carbon dioxide in rats

•Rats were exposed during a single 4 h period to high concentrations of CO2.•Oxygen was not added to keep its concentration constant.•Mortality rate was fitted with the probit function Pr = F(Cnt).•In the range 40-45% CO2 a very high “n” was found (CI: 15.6-32.7).•In the range 44-52% CO2 a meaningful “n” could not be determined.

Subterranean storage of carbon dioxide (CO2) has been proposed to diminish atmospheric increases of this greenhouse gas. To contribute to risk assessment of accidental release associated with handling, transport and storage, rats were exposed to high concentrations (targets 40, 43 and 50 volume %) of CO2. The oxygen concentrations dropped as a result, but were not supplemented. For each concentration, pairs of animals were exposed for different exposure durations to derive an exposure concentration-duration relation in which mortality is described as a function of Cn × t (probit relation). A very high “n” value for the probit function could be derived from the data obtained at 40% and 43% CO2, which indicates that for exposure durations longer than 30 min the LC50 decreases hardly with increasing exposure duration. Below 30 min the LC50 seemed to increase with decreasing exposure durations. The variability in the data of 43% and 50% CO2, however, did not allow to derive a meaningful value of “n”.