Nanoplastic-Induced Developmental Toxicity in Ascidians: Comparative Analysis of Chorionated and Dechorionated Phallusia mammillata Embryos

Nanoplastics pose a growing threat to marine ecosystems, particularly affecting the early developmental stages of marine organisms. This study investigates the effects of amino-modified polystyrene nanoparticles (PS-NH₂, 50 nm) on the embryonic development of <i>Phallusia mammillata</i>, a model ascidian species. Both chorionated and dechorionated embryos were exposed to increasing concentrations of PS-NH₂ so morphological alterations could be assessed with a high-content analysis of the phenotypes and genotoxicity. PS-NH₂ induced the same morphological alterations in both chorionated and dechorionated embryos, with dechorionated embryos being more sensitive (EC₅₀ = 3.0 μg mL^-1) than chorionated ones (EC₅₀ = 6.26 μg mL^-1). Interestingly, results from the morphological analysis showed two concentration-dependent mechanisms of action: (i) at concentrations near the EC₅₀, neurodevelopmental abnormalities resembling the ones induced by exposure to known endocrine disruptors (EDs) were observed, and (ii) at higher concentrations (15 μg mL^-1 and 7.5 μg mL^-1 for chorionated and dechorionated embryos, respectively), a nonspecific toxicity was evident, likely due to general oxidative stress. The phenotypes resulting from the PS-NH₂ treatment were not related to DNA damage, as revealed by a genotoxicity assay performed on neurula embryos. Our data suggest that PS-NH₂-induced toxicity is primarily mediated through oxidative stress, probably triggered by interactions between the positive charges of the PS NPs and the negative charges on the cell membranes. The lack of a protective chorion further exacerbated these effects, highlighting its role in mitigating/protecting against NP-induced damage.