Toxicity of nanoplastics during the embryogenesis of the ascidian Ciona robusta (Phylum Chordata).

Nanoplastics are considered contaminants of emerging concern at the global scale. The recent evidence of their occurrence in seawater from the Mediterranean Sea calls for a thorough evaluation of their impact on marine life and in particular on vulnerable life stages such as planktonic embryos. Here, we investigated the impact of increasing nominal concentrations of 50 nm amino-modified (PS-NH) and 60 nm carboxy-modified (PS-COOH) polystyrene nanoparticles (PS NPs) on the embryonic development of the ascidian (phylum Chordata), a common benthic invertebrate living in Mediterranean coastal areas with the peculiarity of being an early chordate developmental model. A strong agglomeration of PS-COOH (approx. 1 µm) was observed in natural sea water (NSW) already at time 0, while PS-NH resulted still monodispersed (approx. 130 nm) but largely aggregated after 22 h with a microscale dimension similar to those negatively charged. However, their effect on embryos development largely differed at 22 h: PS-COOH did not affect larvae phenotypes nor their development, while PS-NH caused a dose-dependent effect (EC (22 h) of 7.52 μg mL) with various degrees of phenotype malformations (from mild to severe) and impairment of larval swimming. Embryos (up to 30%) exposed to 15 µg mLPS-NH resulted not developed and the majority was unable to hatch. Calculated PS-NH EC resulted higher than those available for other marine invertebrate species, suggesting a protective role of the egg envelopes surrounding embryos toward nanoplastics exposure.