From brood pouch to complex behavior: Tracking nanoplastic toxicity in Daphnia magna

Nanoplastics (NP) are increasingly recognized as pollutants in freshwater systems. Their small size and ability to cross biological barriers make them a concern for aquatic species. The cladoceran Daphnia magna is a keystone species and a useful model to study NP toxicity, although behavioral consequences of NP exposure are poorly understood. The objective in this study was to combine traditional endpoints, such as reproduction and neonate morphology, with a detailed behavioral profile of juveniles and adults, to clarify potential NP effects at concentrations possibly present in the environment (0.1, 1, and 3 mg/L). The assays included reproduction and neonate biometry, as well as light/dark activity, thigmotaxis, and habituation tests in both chronic maternal and acute exposures. Results showed NP accumulation in Daphnia bodies and NP were also detected in embryos inside brood pouches. Chronic maternal exposure reduced fecundity at the lowest dose, altered neonate morphology, and induced stage-dependent behavioral effects, including both hypoactivity and hyperactivity depending on light conditions and doses. Juveniles were more sensitive than adults, showing consistent reductions in edge preference and altered habituation profiles. Acute exposures also affected behavior but to a lesser extent. Together, our results indicate that NP can affect reproduction, development, and behavior in Daphnia, with potential consequences for population growth and predator-prey interactions. In conclusion, this work provides new insight into NP toxicity in a keystone zooplankton species, highlighting the importance of investigating the subtle behavioral endpoints for understanding ecological risks.