The no-observed-adverse-effect level (NOAEL) denotes the level of exposure of an
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
, found by
experiment
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...
or
observation, at which there is no biologically or statistically
significant increase in the frequency or severity of any adverse effects of the tested protocol. In drug development, the NOAEL of a new drug is assessed in laboratory animals, such as
mice, prior to initiation of human trials in order to establish a safe clinical starting dose in humans. The
OECD
The Organisation for Economic Co-operation and Development (OECD; french: Organisation de coopération et de développement économiques, ''OCDE'') is an intergovernmental organisation with 38 member countries, founded in 1961 to stimulate e ...
publishes guidelines for
Preclinical Safety Assessments, in order to help scientists discover the NOAEL.
Synopsis
Some adverse effects in the exposed population when compared to its appropriate control might include alteration of
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
, functional capacity,
growth, development or life span. The NOAEL is determined or proposed by qualified personnel, often a
pharmacologist
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemic ...
or a
toxicologist
Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating expo ...
.
The NOAEL could be defined as "the highest experimental point that is without adverse effect," meaning that under laboratory conditions, it is the level where there are no
side-effects. It either does not provide the effects of drug with respect to duration and dose, or it does not address the interpretation of risk based on toxicologically relevant effects.
In
toxicology
Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating e ...
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.
[Faustman, E.M., Omenn, G.S. Risk assessment. (2001) In: C. D. Klaassen (ed.): Casarett & Doull's Toxicology, 6. ed., McGraw-Hill, New York, pp. 92–94. .]
The NOAEL level may be used in the process of establishing a
dose-response relationship, a fundamental step in most
risk assessment
Broadly speaking, a risk assessment is the combined effort of:
# identifying and analyzing potential (future) events that may negatively impact individuals, assets, and/or the environment (i.e. hazard analysis); and
# making judgments "on the ...
methodologies.
Synonyms
The NOAEL is also known as NOEL (no-observed-effect level) as well as NEC (no-effect concentration) and NOEC (no-observed-effect concentration).
US EPA definition
The
United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
defines NOAEL as 'an 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 as adverse, or as precursors to adverse effects.
In an experiment with several NOAELs, the regulatory focus is primarily on the highest one, leading to the common usage of the term NOAEL as the highest exposure without adverse effects.'
See also
*
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, ...
*
Measures of pollutant concentration Measures of pollutant concentration are used to determine risk assessment in public health.
Industry is continually synthesizing new chemicals, the regulation of which requires evaluation of the potential danger for human health and the environm ...
References
Concentration indicators
Environmental policy in the United States
Food law
Food safety
Food and Drug Administration
Toxicology
United States Environmental Protection Agency
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