Differential effects of pristine and aged polystyrene nanoplastics on the first molting process in Tachypleus tridentatus.

Nanoplastics (NPs) are pervasive marine pollutants, yet most ecotoxicological studies rely on pristine commercial particles, which fail to reflect their transformation in real-world environments and associated ecological risks. As a primitive arthropod, the Chinese horseshoe crab (Tachypleus tridentatus) undergoes its most delicate phase during the initial phase of growth. Here, we examined the impact of pristine versus aged polystyrene (PS) NPs exposure on the initial molting cycle of juvenile T. tridentatus. Aged PS-NPs were prepared using ultraviolet radiation and subsequently exposed to juvenile T. tridentatus at an environmentally informed concentration (100 μg/L) for 90 days. It was revealed by our findings that the molting process was significantly disrupted by exposure to PS-NPs, as evidenced by a reduced molting rate and a prolonged mean molting time. In the pristine PS-NP group, this disruption was accompanied by severe mitochondrial impairment, elevated reactive oxygen species (ROS), and reduced adenosine triphosphate (ATP). Notably, the aged PS-NP group, molting inhibition occurred without measurable ROS or ATP changes, suggesting distinct or additional mechanisms. Changes in the toxicity of aged PS-NPs are associated with alterations to their surface properties. These findings offer a valuable reference for ecotoxicological assessment of aged PS-NPs in horseshoe crabs.