Title: free ion activity model
Long Title: IUPAC Gold Book - free ion activity model
DOI: 10.1351/goldbook.14701
Status: current

Definition
Model for acute metal toxicity to aquatic organisms based on the idea that toxicity occurs when the concentration of the free metal cation in solution reaches a certain level.

Note
This model has been developed into the biotic ligand model.

Related Term
- biotic ligand model: https://goldbook.iupac.org//terms/view/14501

Source
- PAC, 2009, 81, 829. 'Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)' on page 888 (https://doi.org/10.1351/PAC-REC-08-07-09)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/14701/html
- json: https://goldbook.iupac.org/terms/view/14701/json
- xml: https://goldbook.iupac.org/terms/view/14701/xml

Citation: Citation: 'free ion activity model' 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.14701
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Disclaimer: 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.
Accessed: 2026-05-08T08:03:16+00:00