In a Nutshell: Guidance on assessment and application of Adverse Outcome Pathways (AOPs) relevant to the Endocrine System

Various European chemical regulations do not allow the marketing or use of substances known to have endocrine disrupting properties – chemicals that induce adverse effects in humans and/or wildlife as a result of interaction with the endocrine system.

Adverse outcome pathways (AOPs) have the potential to be important tools for the assessment of endocrine disrupting properties as they can help identify if an adverse effect observed in an in vivo (animal based) study can be plausibly linked to a change in the endocrine system. AOPs could potentially be used to help predict the potential for an adverse effect in humans and/or wildlife from the results of in vitro (non-animal based) assays, potentially reducing the requirement for animal testing.

However, if AOPs are to be used to identify and/or predict endocrine disrupting properties, it must be ensured that they are sufficiently robust and fit for purpose. To this end, this Technical Report provides guidance on identifying the basic requirements and how to establish the minimum scientific standards that allow the use of AOPs. The guidance is centred on the different contexts of AOP use such as hazard identification, read-across (predicting potential effects for a chemical based on data for other, similar, chemicals) and risk assessment. These requirements are described as ‘Key Elements in Assessment of AOP Utility’ and cover factors such as ensuring that AOPs are consistent with the current scientific knowledge (Biological Plausibility) and ensuring that any potential differences amongst species are considered (Taxonomic Applicability/Species Concordance).

This guidance will be a useful tool for 1) those looking to develop new AOPs helping to identify the key elements that need to be considered during construction, and 2) those considering applying existing AOPs by providing a list of key elements to be considered to facilitate a critical review and ensure it is fit for the intended purpose.

The document has been published as ECETOC Technical Report no.128: Guidance on assessment and application of Adverse Outcome Pathways (AOPs) relevant to the Endocrine System. The Executive Summary and free PDF of the report are available at