Micro- and nanoplastics in early-life and suggestive developmental toxicity

Micro- and nanoplastics (MNPs) are increasingly recognized as potential contaminants of concern during sensitive developmental windows. This review critically synthesizes current evidence on the developmental and potential transgenerational effects of MNPs exposure, focusing on maternal and paternal exposure pathways, parental-to-offspring transfer, offspring health outcomes, and proposed mechanisms. The available evidence is dominated by experimental studies in rodent model systems, whereas human data remain limited. Overall, parental MNPs exposure has been associated with disturbances in maternal physiology, placental function, fetal development, and postnatal health. Experimental studies have reported MNPs detection in reproductive, placental, fetal, and offspring tissues, although the extent and biological significance of parental-to-offspring transfer remain incompletely understood. Across animal models, parental exposure has been associated with neurodevelopmental, cardiovascular, metabolic, and reproductive abnormalities in offspring, with some studies suggesting effects beyond the directly exposed generation. Studies addressing paternal exposure, germline transmission, and epigenetic inheritance remain scarce, and both the causal roles of proposed mechanisms and the mechanistic distinctions between maternal and paternal transmission pathways remain poorly defined. In addition, data on the maternal–fetal transfer, organ-specific biodistribution, clearance, and toxicokinetics of MNPs are still limited. Importantly, interpretation is constrained by substantial methodological limitations. Most studies use pristine, monodisperse particles, particularly polystyrene, under exposure conditions that may poorly represent environmentally relevant human exposure. Limited particle characterization, insufficient toxicokinetic data, and the scarcity of studies examining weathered plastics, diverse polymer types, additives, and environmentally realistic mixtures further constrain mechanistic interpretation and risk inference. Critical particle behaviors, including aggregation, protein corona formation, gastrointestinal transformation, and pollutant adsorption, are also rarely characterized, creating substantial uncertainty regarding internal dose, bioavailability, and target-tissue exposure. Moreover, the frequent absence of appropriate inert-particle or non-plastic nanoparticle controls complicates the attribution of observed effects specifically to polymer-related toxicity rather than nonspecific particle-induced stress. Overall, current evidence raises concern that parental MNPs exposure may affect developmental health, but it remains insufficient for robust human risk assessment. Future research should prioritize environmentally realistic exposures, standardized particle characterization, mechanistic studies distinguishing direct from inherited effects, and well-designed human studies.