MSC Endorses Hyalella Azteca Test for Bioaccumulation Studies under REACH

The decision supports HYBIT as a valid study method under OECD Test Guideline 321, replacing the Bioaccumulation in Fish study (OECD TG 305) for substances where aqueous exposure is feasible. In cases where aqueous exposure is not possible, the fish study will still be used. The test offers a more ethical and scientifically robust approach, reducing the reliance on vertebrate organisms in line with EU policies promoting animal welfare.

Why the Shift to HYBIT?

The MSC's decision stems from increasing recognition that the Hyalella Azteca test is both scientifically sound and legally justified for a range of substances evaluated under REACH. The test is considered an internationally recognised method within Article 13(3) of the REACH regulation. While relatively new, HYBIT's inclusion marks an important step in applying alternative testing methodologies that align with ethical standards.

Stakeholders voiced concerns over HYBIT’s applicability, particularly for inorganic substances. It was clarified that the OECD has not yet validated HYBIT for these cases, but it remains a viable option for organic substances requiring aqueous exposure testing.

Wider Implications for Regulatory Testing

The approval of HYBIT is part of a broader strategy under REACH to refine substance evaluation processes. By adopting this test, MSC aims to improve the accuracy and relevance of bioaccumulation studies while reducing unnecessary harm to vertebrates. This decision will apply to future dossier evaluations and, where appropriate, in substance evaluation cases.