Time-Dependent Polystyrene Nanoplastic Toxicity in Cherax quadricarinatus: Oxidative Stress, Gut Dysbiosis, and Hepatopancreatic Bioaccumulation

Polystyrene nanoplastic (PS-NP) contamination poses an emerging threat to aquaculture species, yet time-resolved assessments integrating host physiology, gut microbial ecology, and tissue bioaccumulation remain limited. Here, we evaluated the temporal effects of 100 mg/L PS-NPs (100 nm) on Cherax quadricarinatus (Von Martens, 1868) over a 3-week exposure period. Crayfish were assigned to a control group (Group A) and three treatment groups exposed for 1 (Group B), 2 (Group C), or 3 (Group D) weeks. No mortality occurred. Hepatopancreatic antioxidant enzyme activities (superoxide dismutase and glutathione peroxidase) displayed a hormetic response (upregulation at weeks 1–2 followed by depletion at week 3), indicating oxidative stress overload. Alkaline phosphatase activity declined progressively, reflecting cumulative immunosuppression. Histological examination revealed time-dependent structural damage in the hepatopancreas: hepatic tubule enlargement, increased vacuolation, B cell hypertrophy, and cellular disorganization/lysis after three weeks. 16S rRNA sequencing revealed that PS-NPs induced time-dependent gut dysbiosis, characterized by depletion of beneficial taxa and enrichment of opportunistic pathogens. Alpha-diversity metrics (ACE, Chao1, Shannon) were significantly reduced in Group D compared to controls, confirming loss of microbial evenness and richness. Pyrolysis gas chromatography–mass spectrometry quantification demonstrated marked PS-NP bioaccumulation in the hepatopancreas, with concentrations rising from 6.94 μg/g in controls to 65.38 μg/g in Group D, a 9.4-fold increase. Collectively, prolonged PS-NP exposure is associated with oxidative stress, immune dysfunction, progressive gut dysbiosis, and substantial hepatopancreatic nanoplastic burden in C. quadricarinatus. These findings carry implications for ecological risk assessment and highlight the need for further investigation into food safety risks associated with human consumption of crayfish from PS-NP-contaminated environments.