14422 IUPAC Gold Book - acute-to-chronic toxicity ratio 10.1351/goldbook.14422 14422 current initialism: ACR 1 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. 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. acute https://goldbook.iupac.org//terms/view/14421 application factor https://goldbook.iupac.org//terms/view/15121 chronic https://goldbook.iupac.org//terms/view/14524 maximum acceptable toxicant concentration https://goldbook.iupac.org//terms/view/14832 PAC, 2009, 81, 829. 'Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)' on page 835 (https://doi.org/10.1351/PAC-REC-08-07-09) https://goldbook.iupac.org/terms/view/14422/html https://goldbook.iupac.org/terms/view/14422/json https://goldbook.iupac.org/terms/view/14422/plain Citation: 'acute-to-chronic toxicity ratio' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.14422 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-04-20T18:31:24+00:00