https://doi.org/10.1351/goldbook.14422
Numerical dimensionless quantity that is the ratio of an acute toxicity test result (e.g., \(\pu{LC_{50}}\)) to a chronic toxicity test result (e.g., maximum acceptable toxicant concentration, MATC) where both are expressed in the same units (e.g., \(\pu{mg L-1}\)). Ideally, the data are for the same chemical species.
Note: It is in principle the inverse of an application factor and is used in a similar manner. The ACR is commonly used for estimating chronic toxicity of a chemical on the basis of its acute toxicity. The ACR should be greater than one because the ratio compares an acute to a chronic value.