Toxic effects of MPs and Up Grade® herbicide on the Nile tilapia (Oreochromis niloticus): Oxidative stress, immune responses, and histopathological investigations.

This study explored the combined toxicity of polyethylene microplastics (PE-MPs) and the herbicide Up Grade®46% SL (UPGR) on Nile tilapia (Oreochromis niloticus), focusing on antioxidant, immunological, and histopathological responses. Nile tilapias were divided into four groups: control, UPGR exposure (2.916 mg/L), PE-MPs exposure (10 mg/L), and combined PE-MPs and UPGR exposure. Over 15 days, significant changes were observed in various biomarkers. Total antioxidant capacity (TAC) levels significantly decreased in the PE-MPs group compared to the control (p < 0.05), while superoxide dismutase (SOD) levels increased in both PE-MPs and UPGR groups (p < 0.05). The combination group showed significantly elevated levels of immune biomarkers IL-1β and IL-6 compared to individual exposures (p < 0.05). Histopathological examination revealed severe alterations: gills showed degenerated lamellae, malformed secondary lamellae, and congested blood capillaries; intestines had vacuolations, degenerated muscularis, hydropic degeneration, and numerous inflammatory cells; and testes exhibited degraded tubules, pigmentation, few primary spermatogonia, and necrosis of many cysts. The present study indicates that exposure to sub-lethal concentrations of UPGR and PE-MPs individually and in combination for 15 days induce oxidative stress, immunotoxic impairments and cause severe histological changes in the gills, intestines and testes of O. niloticus. The study underscores the urgent need to explore how microplastics interact with other pollutants in aquatic ecosystems, posing combined threats to aquatic life. The observed joint toxicity suggests potential long-term impacts on fish health and calls for comprehensive risk assessments and mitigation strategies to protect aquatic environments from such chemical pollutants.