At the recent Society of Toxicology (SOT) conference, Dr. Ivan Rusyn of Texas A&M University, presented a compelling analysis titled “To Accept or Not to Accept a Read-Across Adaptation: A Systematic Analysis of 15 Years of Testing Proposal Decisions by the European Chemicals Agency”. His talk offered a rare and data-driven insight into the practical outcomes of read-across justifications submitted under EU REACH.
From 2008 to 2023, 2,630 Testing Proposals were submitted to ECHA, of which 1,538 had published decisions. A significant proportion of these included adaptations to standard information requirements – most commonly, analogue or group-based read-across approaches. Dr. Rusyn’s team evaluated all publicly accessible proposals up to August 2023, identifying trends in acceptance and rejection by ECHA.
Key findings revealed that of the 353 Testing Proposals with adaptations, 167 used analogue and 137 used group read-across. Acceptance rates were notably higher for group-based approaches (62%) compared to analogue (38%). Similarity in structure or physico-chemical properties was the most common justification, but ECHA placed greater weight on toxicokinetic considerations and supporting toxicological data (e.g., bridging studies) in its evaluations. Another interesting artefact was an apparent downward trend in acceptance of read-across justifications following ECHA's publication of the read-across assessment framework in 2015, which provided the regulators and industry with a comprehensive series of criteria to assess the robustness of any read-across argument.
Crucially, the study also addressed compliance checks—another major route by which ECHA assesses dossier quality but which are much harder to substantiate. It would appear that ECHA’s scrutiny during compliance checks mirrors that of the Testing Proposal process. In both cases, poorly substantiated read-across justifications – particularly those lacking mechanistic or toxicokinetic support—were commonly rejected. This reinforces the need for robust, well-documented scientific reasoning across all REACH submission routes.
This retrospective analysis is a valuable resource for companies planning to use read-across in future REACH submissions. It highlights the importance of detailed, scientifically grounded justification – especially for analogues – and the growing expectation from regulators for high-quality bridging data to further support the validity of a read-across approach.
At Blue Frog Scientific, we have a strong track record in building strong, defensible read-across arguments that stand up to ECHA scrutiny – whether in Testing Proposals, compliance checks, or dossier updates.
Our regulatory experts can help you assess similarity, design bridging studies, and craft scientifically robust justifications aligned with ECHA's Read Across Assessment Framework. If you’re planning a read-across or need support following an ECHA draft decision, we’re here to help.
