no-observed-effect-level (NOEL)
Greatest concentration or amount of a substance, found by experiment or observation, that causes no alterations of @MT07285@, functional capacity, growth, development, or life span of target organisms distinguishable from those observed in normal (control) organisms of the same species and @S06037@ under the same defined conditions of exposure.
PAC, 1993, 65, 2003. (Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993)) on page 2076 [Terms] [Paper]