ItalyAll these acronyms are parameters employed in toxicology to determine the potential hazard of substances; they are the result of repeated dose toxicity studies carried on animal model systems and are fundamental to understand potential risks to humans exposed to the substance investigated.
Still today there are no consistent standard definitions for the terms NOEL, or NOAEL or the corresponding LOEL and LOAEL.
The most complete and clear definition for NOAEL is “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.”
The highest exposure level at which no effects (adverse or nonadverse) are observed in the exposed population is the NOEL.
The LOAEL corresponds to 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.
It is obvious that, in order to distinguish NOAEL from NOEL, there is a need for definitions of “adverse” and “biologically significant”, especially considering that many organizations will actually be employing NOAELs in their regulatory process even though they may refer to them as a NOELs.
- An adverse effect is defined as a biochemical, morphological or physiological change (in response to a stimulus) that either singly or in combination adversely affects the performance of the whole organism or reduces the organism’s ability to respond to an additional environmental challenge.
- A biologically significant effect is a response (to a stimulus) in an organism or other biological system that is considered to have substantial or noteworthy effect (positive or negative) on the well-being of the biological system. The concept is to be distinguished from statistically significant effects or changes, which may or may not be meaningful to the general state of health of the system.
Bibliography
Carpanini et al TOXICOLOGIC PATHOLOGY, vol 30, no 1, pp 66–74, 2002
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