No-observed-effect level (NOEL) and no-observed-adverse-effect level (NOAEL): use in animal health risk assessments

Since November 2016, the Australian Pesticide and Veterinary Medicines Authority has adopted the use of the terms no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) in evaluations to consider the safety of agricultural chemicals and veterinary medicines.

This decision was taken to harmonise with other regulatory bodies (eg Joint FAO/WHO Expert Committee on Food Additives, Joint FAO/WHO Meeting on Pesticide Residues, European Food Safety Authority, US Environmental Protection Agency, Canadian Pest Management Regulatory Agency).

The following definitions, based on that described in Principles and Methods for the Risk Assessment of Chemicals in Food (2009), WHO Environmental Health Criteria, No. 240 have been adopted:

  • No-observed-adverse-effect level (NOAEL): greatest concentration or amount of a substance, found by experiment or observation, that causes no detectable adverse alteration of morphology, functional capacity, growth, development, or lifespan of the target organism under defined conditions of exposure.
  • No-observed-effect level (NOEL): greatest concentration or amount of a substance, found by experiment or observation, that causes no alteration of morphology, functional capacity, growth, development, or lifespan of the target organism distinguishable from those observed in normal (control) organisms of the same species and strain under the same defined conditions of exposure.

The Australian Pesticide and Veterinary Medicines Authority noted that it had previously used the term NOEL in a manner consistent with the definition as described in 'Principles for the safety assessment of food additives and contaminants in food (1987)', WHO Environmental Health Criteria, No. 70.

This definition includes the statement that the NOEL results in no detectable, usually adverse, alteration of morphology, functional capacity, growth, development, or lifespan of the target.

The Australian Pesticide and Veterinary Medicines Authority notes that its decision to adopt the definition of NOAEL from WHO Environmental Health Criteria No. 240 did not entail any change in its evaluation practice, and was merely harmonizing the terminology used to differentiate between observed effects and observed adverse effects. Hence, this decision had no impact on any of the previous human health risk evaluation conclusions made by the Australian Pesticide and Veterinary Medicines Authority.

All WHO Environmental Health Criteria monographs are available online.

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