Test substance preparation determines the tested fraction and the outcome of human health NAMs for poorly-water-soluble (pre)polymers.

While a comprehensive revision of the REACh regulation is currently no longer under consideration, regulatory requirements potentially covering analytical, ecotoxicological, and toxicological aspects of polymers may still evolve. Regulatory testing typically relies on OECD test guidelines (TGs), which are generally designed for small molecules. According to REACh and following the 3R principles, non-animal methods, also described as new approach methods (NAMs) are the first choice for testing. The applicability of NAMs for polymers, substances with high molecular weights and varying solubility, is limited and test substance application in aqueous media presents a challenge. Standards described for the biological evaluation of medical devices (DIN EN ISO 10993) and food contact materials (DIN EN 13130) offer test substance preparation methods for finished articles including polymer materials. In this study, preparations of seven non-water soluble (pre)polymer materials were selected for testing with four different NAMs: basal cytotoxicity assay, an estrogen receptor transcriptional activation assay (OECD TG 455), in vitro micronucleus test (OECD TG 487) and in vitro skin irritation test (OECD TG 439/ DIN EN ISO 10993). Although the test substance preparation steps developed for finished medical device or food contact products technically allowed testing of all seven (pre)polymers across the four NAMs, this approach is fundamentally limited. Applying standard methods designed for small molecules (e.g., OECD TGs) or finished articles (e.g., ISO standards) to (pre)polymers does not necessarily produce data that realistically reflect bioavailable fractions under intended use conditions. Development of standardized methods for analytical, ecotoxicological and toxicological evaluations is essential for complex test materials such as polymers.