Key OECD Updates Published June 2025
On 25 June 2025, the Organisation for Economic Co-operation and Development (OECD) released 56 updated or corrected Test Guidelines. These changes align with the latest scientific advances and the 3Rs principles (Replacement, Reduction, and Refinement of animal testing).
The updates ensure continued Mutual Acceptance of Data (MAD) across OECD member states and adhering countries. Of the 56 updates, eight are directly relevant to environmental fate and ecotoxicity studies.
OECD Test Guidelines (TGs) Impacted
OECD TG 111: Hydrolysis as a Function of pH.
OECD TG 307: Aerobic and Anaerobic Transformation in Soil.
OECD TG 308: Aerobic and Anaerobic Transformation in Aquatic Sediment Systems.
OECD TG 316: Phototransformation of Chemicals in Water – Direct Photolysis.
OECD TG 203: Fish, Acute Toxicity Test.
OECD TG 210: Fish, Early-Life Stage Toxicity Test.
OECD TG 236: Fish Embryo Acute Toxicity (FET) Test.
OECD TG 254: Mason bees (Osmia sp.), Acute Contact Toxicity Test .
What Changed in Environmental Fate Test Guidelines?
The environmental fate studies (TGs 111, 307, 308, 316) were revised to include clarifications on radioactive labelling:
Updated guidance on radiolabelling position and protocol.
Additional criteria for selecting the appropriate label location.
These updates aim to ensure accurate tracking of labelled compounds and improved consistency across laboratories.
What’s New in Fish Toxicity Guidelines?
For fish ecotoxicology studies (TGs 203, 210, 236), key updates include:
Optional “omics” endpoints – researchers can now collect and cryopreserve tissue samples for advanced molecular investigations (e.g., transcriptomics biomarkers, mode of action studies).
Mechanistic insights – enables early detection of toxic effects and supports next-generation risk assessment frameworks.
Modernisation of TG 203 – significant update to a guideline originally published in 1992, now reflecting modern science and technical considerations such as:
Testing of UVCBs and difficult substances.
Flow-through system guidance.
Expanded technical details for study design and interpretation.
These revisions reflect OECD’s growing commitment to mechanistic toxicology and the integration of non-animal methods into regulatory science.
What’s New in Solitary Bee Acute Toxicity Testing?
This new OECD 254 test guideline describes a laboratory test method, designed to assess the acute contact toxicity of test chemicals to adult solitary bees. It is based principally on the OECD guidelines for the testing of chemicals 214 and 246. Adult female solitary bees are exposed to a range of doses of the test chemical dissolved in an appropriate carrier, by direct application to the dorsal side of thorax. The test duration is 48 h (or up to 96 h, if ongoing mortality makes prolongation necessary) and bees are fed ad libitum with sugar solution throughout the test. Mortality is recorded daily and compared with control values. The results are analysed in order to estimate the LD50 at 48 h, as well as at 72 h and 96 h if the duration of the study is extended. Sublethal effects, if any, should also be recorded.
The Purpose of These OECD Updates
These updates enhance the reliability and regulatory acceptance of environmental fate and ecotoxicity studies worldwide. By modernising test guidelines and introducing optional mechanistic endpoints, OECD is paving the way for:
More robust and predictive hazard assessments.
Early identification of risks using molecular biomarkers.
Better alignment with emerging non-animal and NAMs approaches.
Need Support with OECD Studies?
The June 2025 OECD updates represent meaningful enhancements for environmental risk assessment. If your organisation is planning or currently running studies impacted by these changes, early expert input can save time and costs.
Blue Frog Scientific’s consultants specialise in study design and monitoring under OECD and REACH frameworks. Call or email and speak directly with one of our environmental fate experts or regulatory ecotoxicology consultants.
