ECHA PBT Expert Group Highlights Bioaccumulation Assessment Strategies for Tougher Substances

Why Bioaccumulation Assessment Strategies Are Changing

ECHA notes that the approach needs to work for substances that are hard to test, including cases where fish studies may not capture broader bioaccumulation concerns. Guidance updates in 2023 and 2024 add Hyalella as a test organism and incorporate toxicokinetic data to support evaluation in air-breathing organisms such as mammals.

What Was Discussed: NAMs and Tiered Testing Options

At the 41st PBT Expert Group meeting, ECHA reports presentations on an “Integrated strategy for the assessment of aquatic and terrestrial bioaccumulation” project. The project analysed 231 chemicals and recommended consensus values for log Kow and log Koa.

The tiered approach discussed screening criteria and QSAR predictions alongside an in vitro clearance assay with fish cell lines (OECD TG 319A/B) and an invertebrate bioconcentration test (OECD TG 321). For air-breathing organisms, an in vitro intrinsic clearance assay using rat hepatocytes or S9 was discussed in combination with IVIVE, with in vivo testing positioned as a later step when results remain inconclusive. Caren Rauert (UBA) is quoted as saying: “For most substances a non-vertebrate test option would already be available”.

Implications for Compliance Teams Across the Value Chain

The note is non-binding, but it signals expectations for dossier evidence. Teams preparing REACH registrations, updates, or risk assessments can review fish-only rationales, document applicability domains for any NAMs used, and capture decision logic for combining predictions and test results. ECHA notes the project report will be published early 2026 on the UBA website.

Summary

ECHA’s PBT Expert Group says bioaccumulation assessment strategies are moving beyond fish centred evidence, with Hyalella testing, toxicokinetic data, and greater use of NAMs. A tiered approach combining QSAR, in vitro assays, and targeted follow up testing may shape future dossier expectations under REACH and CLP for regulated companies today.