Chemical safety and biosafety

Adverse Outcome Pathways, Molecular Screening and Toxicogenomics



Survey ON ADVERSE Outcome Pathways (AOPs) to identify development priorities 

The OECD has launched a survey to explore the utility of AOPs for regulatory assessment of chemicals and to identify development priorities. The objective is to collect feedback on how the AOP concept and/or existing AOPs are already being used for regulatory purposes, to understand where they fall short regarding their utility, and to identify what directions and priorities future AOP development work should embrace to increase their impact on regulatory toxicology and chemical risk assessment.

The survey is mainly for chemical safety regulators who are experiencing a transition in their work towards an increased use of ‘alternative’ methods and AOPs. However, stakeholders that come from the regulated community and environmental NGOs are also welcome to participate.  

  • The survey is now closed. Thank you for your submissions.


  • Additional initiatives to promote and contribute to the Adverse Outcome Pathways Development Programme - Deadline for participation is 3 October 2016

The PETA International Science Consortium Ltd. (PISC) is sponsoring a competition to encourage contributions to a collaborative resource for Adverse Outcome Pathway (AOP) development - Flyer - Short Version New


  • Lush Prize 

The OECD has won the Lush prize for its work on Adverse Outcome Pathways. The prize is in recognition of the team's work over many years in promoting a science-based approach towards the management of chemicals.

Lush prize picture of hare trophyThe Lush Prize is an annual award designed to support organisations working to replace animal testing with scientifically valid non-animal methods.

Lush Prize judges are distinguished scientists and campaigners who believe that “mapping the ‘human toxicity pathway’ represents a breakthrough moment”.

The video on the right explains more about OECD work on Adverse Outcome Pathways and scientific developments in this area. 

What is an Adverse Outcome Pathway (AOP)

In 2012, the OECD launched a new programme on the development of Adverse Outcome Pathways. An Adverse Outcome Pathway (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). AOPs are the central element of a toxicological knowledge framework being built to support chemical risk assessment based on mechanistic reasoning.

Figure: schematic representation of the Adverse Outcome Pathway (AOP) illustrated with reference to a number of pathways.

AOP image 

‌‌‌The AOP development programme addresses the needs of:

  • the OECD Test Guidelines Programme for the identification of new biomarker endpoints and  in vitro test methods that are candidates to become part of OECD Test Guidelines
  • the OECD QSAR Project for the identification of new methods/profilers for grouping chemicals, and
  • the OECD Hazard Assessment activities for the development of Integrated Approaches to Testing and Assessment (IATA), also known as Integrated Testing Strategies, for defined hazard endpoints
  • Hazard assessment programmes in member countries that seek to establish relationships between early biological responses in cells, tissues, organs and adverse outcome in organisms and/or population using existing data

The OECD co-ordinates its activities with the WHO/IPCS work on Mode of Action, as the AOP concept and the Mode of Action are closely related.





Guidance, template, format available
AOP project proposal form

Note: With experience gained from the AOP developers and the development of the Users' handbook, some parts of the Guidance Document below have become obsolete.  An updated version of the GD will be available in 2016.

Guidance document and template for developing and assessing adverse outcome pathways

(Series No. 184, Series on Testing and Assessment)

User Handbook

AOP for skin sensitisation: Part 1 - Scientific Evidence

AOP for skin sensitisation: Part 2 - Use of the AOP to Develop Chemical Categories and Integrated Assessment and Testing Approaches

(Series No. 168, Series on Testing and Assessment)


How to make a project proposal

Project proposals for developing an AOP can be sent to the OECD Secretariat using the submission of proposals form (word file). Government representatives, academic experts, industry experts, non-governmental organisations, scientific societies, etc. can submit project proposals. The National Coordinators of the Test Guidelines Programme are also available for queries, and should be informed about proposals submitted.

Project proposals are reviewed twice a year and included in the AOP workplan if justified. Browse the list of projects already in the workplan.


Process for the development of AOP at OECD

This flow diagram shows how AOPs are developed, reviewed, agreed and published at the OECD. The publication of an AOP descriptive document in the Series on Testing and Assessment does not preclude the publication by authors of the AOP of scientific articles in the peer-reviewed literature; in fact, broad distribution of the resulting products is encouraged.

Most of the AOP development and review is intended to take place via a web-based IT management tool (“AOP Knowledge Base”) which was publically launched in September 2014.  

Once developed and reviewed by the Advisory Group on Molecular Screening and Toxicogenomics, and other relevant expert groups under the Test Guidelines Programme, the AOP is endorsed by the Working Group of the National Coordinators of the Test Guidelines Programme and the Task Force on Hazard Assessment, and declassified by the Joint Meeting overseeing the OECD work on chemical safety.


AOP Knowledge Base

The AOP Knowledge Base (AOP KB) is 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. The project is jointly led by the OECD, the U.S. Environmental Protection Agency and the European Commission's Joint Research Center.

  • The first AOP KB module is the AOP Wiki: an interactive and virtual encyclopaedia for AOP development. It is structured in accordance with the original OECD "Guidance document and a template for developing and assessing adverse outcome pathways" (Series No. 184, Series on Testing and Assessment) and the more recent Handbook for AOP developers. The Wiki provides developers the necessary steps to capture the scientific information in a user-friendly manner.

  • In the future, it is forseen that other modules of the AOP KB, e.g. Effectopedia, become available. Effectopedia is a knowledge aggregation and modeling platform designed for collaborative development and utilisation of AOPs. Originally built as a standalone project, Effectopedia is currently integrated as part of AOP KB. Effectopedia has a visually expressed modular structure providing easy-to-interpret summary information, supporting experimental evidence, as well as detailed descriptions of the underlying data and assumptions. This design places it at the forefront of AOP research, helping industry, governments and regulatory agencies to make toxicological predictions while simultaneously keeping the information open and accessible for nonprofit organisations and the general public. The first quantitative AOP examples are currently being developed in Effectopedia and it is expected that Effectopedia is released for beta testing in the first quarter of 2016.


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