Technical challenges of testing polymer materials in OECD test guideline methods addressing effects on human health,...

Polymers are substances composed of molecules containing repeating monomer units and exhibiting a distribution of molecular weights due to differences in chain length. This inherent heterogeneity distinguishes them from discrete molecules and may complicate the application and interpretation of standardized hazard assessment procedures. Polymers have been exempt from REACH registration since its inception. While a formal revision of the REACH Regulation is currently no longer anticipated, discussions on introducing additional information requirements for certain polymers remain ongoing through implementing measures and comitology processes. These may include analytical, ecotoxicological, and toxicological data. Standardized regulatory testing typically relies on OECD test guidelines (TGs), which were primarily developed for well-defined chemical substances. Their applicability to polymers, with their molecular weight distribution, heterogenous composition and often challenging physiochemical properties, remains uncertain. The present study evaluates the technical applicability of four guidelines (OECD TG 120 (solution/extraction behavior of polymers in water), OECD TG 202 (Daphnia sp. acute immobilization), OECD TG 439 (in vitro skin irritation using reconstructed human epidermis), and OECD TG 487 (in vitro mammalian cell micronucleus test)) to 17 polymer materials. Testing was conducted in water, cell-culture media, and at the air-liquid interface. Results show that TG 120's sample preparation methods were not universally applicable. TG 202 is generally suitable for water-soluble polymers, however, reactive and poorly soluble polymers present challenges. TG 487 is only applicable to water-soluble polymers, and TG 439 is technically broadly applicable if the test material is pipettable or spoon-applicable. Our findings highlight the limitations of current OECD TGs for polymers and emphasize the need for adapted, standardized methods. This work cautions against indiscriminate use of existing TGs tailored for small molecules and supports the development of polymer-specific testing strategies to ensure reliable and accurate regulatory evaluation.