Key messages

• The human relevance of testing strategies using toxicity studies in experimental animal studies and/or New Approach Methodologies (NAMs ↗) is usually uncertain.
• A pragmatic workflow for human relevance assessment of Adverse Outcome Pathways (AOPs ↗) and NAMs would greatly help to overcome this challenge.
• By testing the workflow in two realistic case studies, we succeeded in making various improvements, both to the workflow itself as well as to the accompanying guidance and templates.

Overview

Understanding whether scientific evidence and test methods accurately reflect effects on human health is essential for reliable chemical safety assessments ↗; this is typically referred to as 'human relevance'. The project aims to improve how human relevance is evaluated. The workflow focuses on toxicological pathways, known as AOPs, that describe the mechanisms via which a chemical can induce adverse health effects. The workflow encompasses a structured, step-by-step evaluation for assessing whether AOPs, and the test methods used to study them, are applicable to humans.

In collaboration with the European agencies EFSA ↗ and ECHA ↗, the project team tested the workflow using two case studies that represent different levels of expected human relevance. Based on the findings, the workflow and supporting materials were improved to enhance clarity, usability, and scientific consistency. This work contributes to better integration of non-animal testing methods ↗ in risk assessment and supports more human-relevant decision-making. 

Achievements & Results

Building on previous work ↗, the project delivered an improved version of the workflow for human relevance assessment of AOPs and NAMs, including updated guidance, structured templates, and a curated toolbox of supporting resources. Insights from two case studies led to clearer criteria for evaluating biological and empirical evidence, more consistent weight-of-evidence assessments, and better handling of context-specific factors such as age, sex, and tissue sensitivity. Input from (regulatory) scientists with different areas of expertise was instrumental to better align the workflow with practical needs, increasing its potential for future regulatory use. The refined workflow is now more user-friendly, adaptable, and better equipped to support modern, non-animal testing strategies in human health risk assessment. 

Policy relevance

The project supports European-wide goals to better utilize human-relevant scientific knowledge in chemical safety assessments and to reduce the use of experimental animals for toxicity testing. Developed with input from EFSA and ECHA, the workflow is aligned with current and near future regulatory needs and next-generation risk assessment approaches.