Lowest-observed-adverse-effect level

The lowest-observed-adverse-effect level (LOAEL), or the lowest-observed-adverse-effect concentration (LOAEC), is the lowest concentration or amount of a substance found by experiment or observation that causes an adverse alteration of morphology, function, capacity, growth, development, or lifespan of a target organism distinguished from normal organisms of the same species under defined conditions of exposure. Federal agencies use the LOAEL during risk assessment to set approval standards below this level.

Source: Wikipedia — Lowest-observed-adverse-effect level (CC BY-SA 4.0)