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Minimal Risk Level (MRL
) is an estimate of daily human exposure to a dose of a chemical that is likely to be without an appreciable risk of adverse non-cancerous effects over a specific duration of exposure.
The no observed adverse effect level (NOAEL
) denotes the level of exposure of an organism
, found by experiment
, at which there is no biologically or statistically significant
(e.g. alteration of morphology
, functional capacity, growth
, development or life span) increase in the frequency or severity of any adverse effects in the exposed population when compared to its appropriate control. 
it is specifically the highest tested dose or concentration of a substance (i.e. a drug or chemical) or agent (e.g. radiation), at which no such adverse effect is found in exposed test organisms where higher doses or concentrations resulted in an adverse effect.[
The lowest-observed-adverse-effect level (LOAEL
) 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.