Expert Report: Advancing OECD TG 309 biodegradation testing

This expert meeting report highlights key findings from ECETOC discussions on improving the OECD Test Guideline 309, which is used to assess the biodegradation of chemicals in surface water. The meeting brought together experts from industry, academia and regulatory authorities to examine the test’s environmental relevance, variability and reliability for regulatory persistence assessments.

The report summarises key insights, including the strong influence of surface-water inoculum and test conditions on degradation outcomes. It presents practical short-term recommendations to improve current testing, alongside longer-term research priorities aimed at strengthening the robustness, comparability and regulatory interpretation of OECD TG 309 studies.