Polystyrene Nanoplastics Induce Multi-Organ Toxicity in the Rainbow Trout (Oncorhynchus mykiss): An Integrated Assessment of Physiological, Immunological, and Molecular Responses

Plastics constitute a major category of waste in aquatic ecosystems, significantly exacerbating environmental pollution and endangering marine organisms. Examining plastic pollution in these ecosystems is essential for understanding its effects and formulating appropriate strategies for their protection. This study investigated the toxicity resulting from 28-days of exposure to different concentrations of polystyrene nanoplastics (PS-NPs; average size 73 nm; T1–0.1, T2–10, and T3–100 mg/kg of diet). After a 28-day exposure to PS-NPs, the growth performance, hematological and immunological indices, antioxidant parameters, plasma cortisol levels, tissue histopathology, and gene expression in Oncorhynchus mykiss liver and spleen were examined. Examining plastic pollution in aquatic ecosystems is essential for understanding its impact and formulating appropriate strategies to safeguard their health. Our findings indicate that PS-NPs significantly affected the physiology and histopathology of O. mykiss , with the severity of effects being dose-dependent. The survival rate of the fish decreased significantly, and most immuno-hematological parameters, as well as electrolyte levels (sodium and potassium), showed a marked decline compared to the control group; however, lymphocyte counts increased. The activity of the antioxidant enzyme SOD exhibited a decreasing trend, whereas ROS activity and the relative expression levels of HSP-70 and TNF-α (in both tissues), as well as SOD (in the liver), increased, and IL-10 (in both tissues) decreased with higher concentrations of PS-NPs. Moreover, blood glucose and cortisol levels exhibited significant dose-dependent reductions. Histopathological analysis indicated moderate to severe changes in the liver, spleen, and intestinal tissue of the group subjected to a dietary exposure of 100 mg/kg of PS-NPs. The findings demonstrate that PS-NPs negatively impacted the physiology, immune response, and gene expression in the rainbow trout. This indicates that particulate plastic pollution adversely affects aquatic organisms and may also threaten human health via the food chain and the chemical toxicity of these particles.