Developmental toxicity of microplastics in human stem cells using adverse outcome pathway based integrated approaches to testing and assessment approach.

Micro/nanoplastics (MNPs), detected in human tissues including the placenta, raise significant concerns regarding their potential impact on early human development. However, the mechanisms underlying their developmental toxicity remain poorly understood. To address this, we applied an Integrated Approaches to Testing and Assessment (IATA) framework to evaluate the developmental toxicity of polystyrene (PS) MNPs by combining adverse outcome pathway (AOP) development, experimental testing within an Integrated Testing Strategy (ITS), and literature-based data integration. As part of the ITS, experimental evaluations were conducted using human embryonic stem cells (ESCs) to assess PS MNP uptake, effects on germ layer differentiation, and size-dependent cytotoxicity. To further refine the assessment, an IATA approach was applied by integrating independent findings from the literature, strengthening the weight of evidence for AOP-based hazard evaluation. The alignment between ESC-based results and broader toxicological data enhances the predictive capacity of developmental toxicity assessments and supports the regulatory application of non-animal testing strategies. These findings contribute to the advancement of mechanism-based, human-relevant toxicity evaluation and provide a structured framework for assessing the developmental risks associated with emerging contaminants like MNPs.