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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.

At the 2025 Conferences of the Parties (COPs) to the Basel, Rotterdam, and Stockholm Conventions, held from April 28 to May 9 in Geneva, significant strides were made in global chemical safety. Notably, the Stockholm Convention introduced stringent measures targeting hazardous substances, while the Basel and Rotterdam Conventions advanced efforts in waste management and chemical trade regulations.

Stockholm Convention: Key Chemical Bans and Restrictions

At the 12th Conference of the Parties (COP-12) of the Stockholm Convention, the parties agreed to list the following substances in Annex A (elimination):

• Chlorpyrifos – A widely used organophosphate pesticide associated with neurodevelopmental harm. Although it will be banned globally, 22 specific exemptions were granted for continued use in certain applications.

• Long-chain perfluorocarboxylic acids (LC-PFCAs) – A group of PFAS substances known for their persistence and potential health impacts. Exemptions were approved for certain uses, such as in semiconductors, electronics, and textiles.

• Medium-chain chlorinated paraffins (MCCPs) – Used as flame retardants and plasticizers. MCCPs were added due to concerns over persistence, bioaccumulation, and toxicity. Exemptions apply to defined industrial uses.

In addition, exemptions for UV-328, a UV stabilizer listed in Annex A in 2023, were reopened and extended. These new exemptions cover specific uses in aviation and industrial settings, which is a rare instance of amending a previously agreed-upon elimination decision post-adoption.

Basel and Rotterdam Conventions: Complementary Advances

While the Stockholm Convention focused on POPs, the Basel and Rotterdam Conventions addressed related challenges.

• Rotterdam Convention (COP-11): Parties agreed to list several additional chemicals in Annex III, which requires prior informed consent (PIC) for international trade. However, the listing of acetochlor and carbosulfan was blocked by a few parties, continuing a trend of stalled listings due to lack of consensus.

• Basel Convention (COP-16): Parties adopted new technical guidelines to improve the management of e-waste, including devices containing POPs. Progress was also made on guidance addressing plastic waste and chemicals of concern in waste streams.

Implications and Next Steps

These decisions mark a significant advancement in global efforts to protect human health and the environment from hazardous chemicals. However, the expanded exemptions, particularly for chlorpyrifos and UV-328, have raised concerns among health and environmental advocates. Continuous monitoring and future negotiations will be crucial to ensure that these measures effectively mitigate risks associated with these substances.