Title: hazard quotient
Long Title: IUPAC Gold Book - hazard quotient
DOI: 10.1351/goldbook.14737
Status: current

Definition
Ratio of toxicant exposure (estimated or measured) to a reference value regarded as corresponding to a threshold of toxicity; often this is determined as the predicted environmental concentration (PEC) divided by the predicted no-effect concentration (PNEC).

Note
If the hazard quotient exceeds unity, the toxicant may produce an adverse effect, but normally this will require an HQ of several times unity; an HQ of less than one indicates that no adverse effects are likely over a lifetime of exposure.

Related Terms
- predicted environmental concentration: https://goldbook.iupac.org//terms/view/14944
- predicted no-effect concentration: https://goldbook.iupac.org//terms/view/14945

Source
- PAC, 2009, 81, 829. 'Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)' on page 895 (https://doi.org/10.1351/PAC-REC-08-07-09)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/14737/html
- json: https://goldbook.iupac.org/terms/view/14737/json
- xml: https://goldbook.iupac.org/terms/view/14737/xml

Citation: Citation: 'hazard quotient' 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.14737
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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: 2026-04-21T15:08:07+00:00