Testing of chemicals

Adverse Outcome Pathways, Molecular Screening and Toxicogenomics


The OECD Environmental, Health and Safety (EHS) Programme has been helping member countries to make better use of increased knowledge of how chemicals induce adverse effects in humans and wildlife, through the so-called Adverse Outcome Pathways.


What's new?

  • Nine AOPs were published in iLibrary on 16 December, following scientific review and OECD endorsement. This new release includes four single AOPs and a network of five AOPs addressing various toxicological and ecotoxicological pathways:
  • 14 December 2022 | Webinar on recent improvements and future challenges for the Adverse Outcome Pathway (AOP) framework and the AOP-Wiki - Watch the webinar replay and access the presentations here.
  • Cooperation with Scientific Journals:

In October 2022, two scientific journals, respectively ALTEX - Alternatives to Animal Experimentation and Cancers signed a Memorandum of Understanding (MOU) with the OECD on co-operative activities in the field of Adverse Outcome Pathway (AOP) development, in order to increase the number of AOPs developed, reviewed and published. In total, the OECD has now signed a MOU with four scientific journals and is seeking more journals to join in. More information is available here.


What is an Adverse Outcome Pathway?

The OECD launched a new programme on the development of Adverse Outcome Pathways (AOP) in 2012. An AOP is an analytical construct that describes a sequential chain of causally linked events at different levels of biological organisation that lead to an adverse health or ecotoxicological effect (see figure below). AOPs are the central element of a toxicological knowledge framework being built to support chemical risk assessment based on mechanistic reasoning.


Schematic representation of the AOP illustrated with reference to a number of pathways

AOP image


Watch our video: OECD work on Adverse Outcome Pathway


Publications on Adverse Outcome Pathways

Access all publications on Adverse Outcome Pathways. Find the OECD Series on Adverse Outcome Pathways on iLibrary  .


The AOP Development Programme

The AOP development programme is overseen by the Extended Advisory Group on Molecular Screening and Toxicogenomics (EAGMST). EAGMST members play an active role in the development of AOPs and can provide support to AOP authors during the development of an AOP in the AOP Wiki.


Representation of the AOP Development Process at the OECD

‌ AOP development process


Cooperation on scientific review and AOP publication

The OECD is developing co-operation with Scientific Journals for the review and publication of AOPs.

This cooperation is formalised in the signature of a Memorandum of understanding (MOU). Scientific Journal Signatories take part in the scientific review of AOPs relevant to their field of expertise, with the view to achieve the following common objectives:

  • Increase the rate of AOP scientific reviews;
  • Offer the opportunity for journals to get more submissions for scientific articles;
  • Enable a double recognition through AOP publications in the scientific literature and at the OECD.

The conditions of the MOU are summarised here.

The following Journals have already signed an MOU with the OECD:


AOP Knowledge Base and Tools

The OECD's AOP Knowledge Base tools, constantly developed and refined, are a web-based platform which aims to bring together all knowledge on how chemicals can induce adverse effects, therefore providing a focal point for AOP development and dissemination.

Logo e AOP Portal


  • The e AOP Portal is the main entry point of the AOP Knowledge Base. The Portal enables search by keywords in AOP titles and key events in the AOP Wiki. It houses the status of all AOPs in the OECD Work Plan and the official copy of OECD endorsed AOPs.

AOP Wiki logo

  • The AOP Wiki represents a joint effort between the European Commission - DG Joint Research Centre (JRC) and U.S Environmental Protection Agency (EPA). It represents the central repository for all AOPs developed as part of the OECD AOP Development Programme and provides a system that organises, via crowd-sourcing, the available knowledge and published research into a verbal description of individual pathways, using a user-friendly Wiki interface. Information on AOP is collected in a qualitative and narrative way.



Missed our previous webinars on AOPs? Watch the video recordings


Find out more

Test Guidelines Programme

The OECD Test Guidelines Programme for the identification of new biomaker endpoints and in vitro test methods that are candidates to become part of OECD Test Guidelines.

Hazard Assessment Activities

The OECD Hazard Assessment activities for the development of Integrated Approaches to Testing and Assessment (IATA, using AOPs as a framework.
The OECD QSAR project for the identification of new methods/profilers for grouping chemicals.




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