Table 2 Definitions of LOAEL, NOAEL and NOEL by three steps of weight-based classification in toxicity test

Weight-based classification	Definitions of criteria	Criteria of toxicity	Evaluation endpoints
Important compound-related changes	․The lowest exposure level at which there are statistically or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control.	Criteria oftoxicity	LOAEL
Minor compound-related changes	․The highest exposure level at which there are no statistically or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control.․Some effects may be produced at this level, but they are not considered to be adverse or precursors to adverse effects.	Non-adverseeffect	NOAEL
Noncompound-related changes	․The highest exposure level at which there are no effects (adverse or nonadverse) observed in the exposed population, when compared with its appropriate control.	No effect	NOEL