lowest-observed-effect-level (LOEL)

Lowest concentration or amount of a substance, found by experiment or observation, that causes any alteration in morphology, functional capacity, growth, development, or life span of target organisms distinguishable from normal (control) organisms of the same species and strain under the same defined conditions of exposure.
See also: lowest-observed-adverse-effect-level, no-observed-adverse-effect-level, no-observed-effect-level
PAC, 1993, 65, 2003. 'Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993)' on page 2065 (https://doi.org/10.1351/pac199365092003)