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Polystyrene nanoplastic exposure induces immobilization, reproduction, and stress defense in the freshwater cladoceran Daphnia pulex
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Researchers documented how polystyrene nanoplastics accumulate in the guts of the freshwater crustacean Daphnia pulex and cause chronic toxicity at environmentally relevant concentrations, delaying reproduction, reducing offspring numbers, and inducing then suppressing antioxidant defense genes over a 21-day exposure.
The widespread occurrence and accumulation of plastic waste have been globally recognized as a critical issue. However, there is limited information on the adverse effects of nanoplastics on freshwater invertebrates. In this study, the effects of a polystyrene nanoplastic on physiological changes (e.g., survival, growth, and reproduction) and expression levels of stress defense genes (oxidative stress-mediated and heat shock proteins) in the freshwater flea Daphnia pulex were measured. The results showed that the digestive organs of D. pulex were strongly fluorescent after exposure to the nanoplastic particles, and the 48-h median lethal concentration (LC 50) of the nanoplastic was determined to be 76.69 mg/L. In the 21-day chronic toxicity test, dose- and time-dependent relationships were observed for body length, and the time to first eggs was significantly prolonged in the 0.5 and 1 mg/L groups. The time to clutch was delayed, and total offspring per female and number of clutches were decreased in all the treatment groups. In addition, the offspring per clutch were significantly decreased in the 0.1 mg/L group. As the nanoplastic concentration increased, expression of stress defense genes (SOD, GST, GPx, and CAT) was first induced and then inhibited. The gene expressions of heat shock proteins (HSP70 and HSP90) were induced in all the treatment groups. Our results suggest that nanoplastics can be ingested by the freshwater cladoceran D. pulex and affect its growth and reproduction as well as induce stress defense.
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Researchers exposed the freshwater zooplankton Daphnia pulex to polystyrene microplastics and observed dose-dependent effects on survival, antioxidant capacity, and energy metabolism. The study found that microplastics accumulated in the digestive tract, caused lipid oxidative damage, disrupted sugar and fat metabolism, and activated DNA repair mechanisms while inhibiting lipid metabolism pathways.
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Researchers exposed the freshwater crustacean Daphnia galeata to polystyrene nanoparticles and observed significant decreases in survival, reproduction, and embryonic development. Using fluorescence microscopy, they tracked the particles as they transferred from external body surfaces to internal organs including the ovaries and brood chamber. The study also found that exposed adults had fewer and smaller lipid droplets, suggesting that nanoplastics disrupt energy storage and reproductive capacity in these organisms.
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Researchers exposed water fleas (Daphnia pulex) to environmentally realistic nanoplastic concentrations across three generations over 63 days. They found that while the first two generations showed mainly molecular-level stress responses, the third generation experienced reduced growth and reproduction along with suppressed antioxidant defenses. The study suggests that even very low nanoplastic concentrations can have significant long-term toxic effects that worsen across generations and may take multiple generations to recover from.
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Polystyrene nanoplastic induces ROS production and affects the MAPK-HIF-1/NFkB-mediated antioxidant system in Daphnia pulex
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Researchers exposed the freshwater crustacean Daphnia pulex to polystyrene nanoplastics and found dose-dependent overproduction of reactive oxygen species (ROS) alongside activation of the MAPK-HIF-1/NFkB stress-signaling cascade, revealing that epigenetic and oxidative pathways mediate nanoplastic toxicity in zooplankton.
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