Feasibility assay for OECD 305 aqueous exposure test

SETAC Europe 2026 -- The OECD 305 guideline provides a standardised approach for evaluating the bioaccumulation potential of a test item through aqueous exposure or a dietary route in fish. Radiolabelled test items are typically used to allow assessment of exposure concentrations in water or feed and the accumulation, metabolism and elimination of the test item in fish. The preferred testing route is through aqueous exposure, particularly for stable organic chemicals with log KOW values between 1.5 and 6.0. For highly hydrophobic substances with very low water solubility, conducting an aqueous exposure test may be challenging. A feasibility assay has been developed to support decision‑making in cases where a regulatory authority requests an aqueous OECD 305 study, but the properties of the test item suggest that such an approach may not be suitable. The assay evaluates whether a stable and measurable dissolved concentration of the test item can be achieved in a dose solution and test water at the required exposure concentration.