Glossary / Toxicology
LOAEL
LOAEL, the Lowest Observed Adverse Effect Level, is the lowest dose or exposure in a toxicity study at which a statistically or biologically significant harmful effect is observed compared with an unexposed control group.
Explanation
The LOAEL sits one step above the NOAEL in a dose-response study. If researchers test several doses and see no harm at the first two but harm at the third, the second is the NOAEL and the third is the LOAEL. When no dose was low enough to avoid harm, there is only a LOAEL and no NOAEL.
This situation is common and important. If a study never found a no-effect dose, risk assessors can start from the LOAEL, but they usually apply an extra uncertainty factor to account for the fact that the true no-effect level is lower still. The adjustment makes the resulting safe-level estimate more cautious.
Like the NOAEL, the LOAEL depends on which doses the investigators chose and how many animals they used. A different design could have given a different value. The effect must also be adverse rather than a harmless biological change, and judging that is a matter of scientific interpretation.
Neither value is a workplace limit. They are inputs to risk assessment and exposure limit setting, and the SDS reports them only where studies exist.
What to do and watch for
- Read the LOAEL with the effect described, as the seriousness of the effect matters more than the number.
- Do not treat the dose just below a LOAEL as safe for people.
- Check Section 8 of the SDS for actual exposure limits and controls.
Where it appears on an SDS
- Section 11: Toxicological information. Where a study found effects at every tested dose, the LOAEL may be given with species, route, duration and observed effect.
- Section 12: Ecological information. Environmental toxicity entries may state a lowest observed effect concentration, the aquatic parallel.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.