Embryonic exposure to polystyrene nanoplastics alters developmental, antioxidant and metabolic responses without detectable short-term behavioral impairment in Plestiodon chinensis.

Terrestrial soils are major sinks for nanoplastics, threatening soil-dwelling oviparous reptiles that lay permeable eggs. The present study investigated the effects of embryonic exposure to an environmentally relevant dose of polystyrene nanoplastics (PS-NPs; 1 mg/L) during incubation in the Chinese skink (Plestiodon chinensis). PS-NPs penetrated eggshells and accumulated in embryos, slowing egg growth, prolonging incubation, triggering oxidative stress, and altering immune-related responses. Crucially, the oxidative stress response was associated with different developmental stages, reflecting the lower functional capacity of early-stage antioxidant systems that rely heavily on non-enzymatic defenses. In contrast, no significant differences were detected in hatchling locomotor performance, boldness, or activity under the behavioral conditions tested. Untargeted metabolomic profiling further identified differences in several important metabolites in hatchlings exposed to PS-NPs. Collectively, these findings indicate that embryonic exposure to PS-NPs is associated with measurable changes to developmental, antioxidant and metabolic responses, while not producing detectable short-term behavioral impairment under the conditions tested in this study. Notably, this study provides the first evidence that antioxidant responses to nanoplastic exposure differ between developmental stages in reptiles. This offers novel insights into the physiological vulnerabilities of oviparous wildlife to soil pollution, and highlights the need to incorporate multiple developmental stages when conducting risk assessments for environmental contamination.