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Differential effects of pristine and aged polystyrene nanoplastics on the first molting process in Tachypleus tridentatus
Summary
Scientists found that tiny plastic particles (nanoplastics) harm baby horseshoe crabs by disrupting their ability to molt, or shed their shells to grow, a critical step for survival. Surprisingly, "weathered" plastic particles (the kind that break down from sunlight exposure in real oceans) caused this harm through different, less-understood mechanisms than fresh plastic particles typically used in lab studies. This matters because most plastic pollution in the environment is aged, not fresh, meaning current safety testing may be underestimating real-world risks to marine life, and potentially to the seafood humans eat.
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.