OECD Publishes New and Revised Test Guidelines for Chemical Safety Assessment

On 25 June 2025, the Organisation for Economic Co-operation and Development (OECD) published 56 new, updated, and corrected Test Guidelines for the testing of chemicals. These guidelines, available in both English and French, aim to ensure that chemical safety testing remains aligned with scientific progress and best practices. The update also strengthens the application of the Replacement, Reduction and Refinement (3Rs) principles on animal testing, ensuring that the resulting data remains covered by the OECD Mutual Acceptance of Data (MAD) framework in all member and adhering countries.

Key Highlights of the 2025 Update

• New Test Guideline on Mason Bees:

The update introduces Test No. 254: Mason bees (Osmia sp.), Acute Contact Toxicity Test, marking the first OECD test guideline dedicated to solitary bee species. This test complements existing honeybee assessments and supports pollinator protection efforts.

• Omics Data Collection Integrated into Several Tests:

Seven existing guidelines have been updated to permit the collection of tissue samples for omics analysis, thereby supporting molecular-level toxicity assessments. The affected tests include:

• • Test No. 203 (Fish, Acute Toxicity Test)

  • Test No. 210 (Fish, Early-life Stage Toxicity Test)

  • Test No. 236 (Fish Embryo Acute Toxicity Test)

  • Test Nos. 407, 408, 421, and 422 (Various rodent toxicity and reproductive screening tests)

• New Defined Approach for Eye Irritation from Surfactants:
  Test No. 467 has been updated to include a defined approach tailored for surfactant chemicals. Test No. 491 now features the new STE 0.5 method as part of this approach.

• Enhanced Skin Sensitisation Assessments:
  Test No. 497 now allows in vitro and in chemico methods (TG 442C, 442D, and 442E) as alternative sources of information and introduces a new defined approach for determining points of departure in skin sensitisation studies.

• Additional Notable Updates and Corrections:

  • Analytical clarifications (Test No. 239)

  • Removal of the EpiSkin™ model from Test Nos. 431 and 439

  • Addition of a new IL-2Luc LTT assay (Test No. 444A)

  • Further guidance on eye histopathology (Test No. 437)

  • Sub-categorisation in skin sensitisation assays (Test No. 442B)

  • Expanded endpoints in reproductive toxicity studies (Test No. 443)

  • Borderline ranges introduced in Test No. 442C

  • Data interpretation improvements for Test No. 456

  • Clarifications on the usage of historical control data (Test Nos. 470 and 488)

  • Refinements in pesticide residue stability testing (Test No. 506)

  • Corrections related to radioactive labelling (Test Nos. 111, 307, 308, and 316)

  • A correction to Test No. 492 on eye irritation classification

Broader Context and Purpose

The OECD Test Guidelines are internationally recognized as standard methods for assessing the safety of chemicals in relation to both human health and the environment. Used by government, industries, and academic institutions, they form part of the OECD Council Decision on Mutual Acceptance of Data (MAD). The guidelines cover areas including physical-chemical properties, effects on biotic systems, environmental fate and behaviour, health effects, and other specialized test methods.

These updates reflect the OECD’s ongoing efforts to ensure that testing methods remain scientifically relevant, internationally harmonized, and responsive to evolving regulatory needs.

The full list of Test Guidelines and details of the 2025 updates are available on the OECD website here.