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

The Australian Pesticide and Veterinary Medicines Authority has reconsidered the use of the terms no-observed-effect level (NOEL), no-observed-adverse-effect level (NOAEL) and the related terms lowest-observed-effect level (LOEL) and lowest-observed-adverse-effect level (LOAEL) in evaluations to consider the safety of agricultural chemicals and veterinary medicines.

Taking into account accepted international best practice by other risk assessment agencies, it has been decided 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) and differentiate between the terms NOAEL and NOEL for the evaluation of pesticides and veterinary drugs.

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 used the 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 does not entail any change in its evaluation practice.

It is merely harmonizing the terminology used to differentiate between observed effects and observed adverse effects. Hence, this decision has 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.

The above changes will come into effect from November 2016.

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