Integrated biomarker, histopathological and genotoxicity-based toxicological evaluation of polystyrene and polyethylene microplastics in Oreochromis mossambicus

Abstract

Microplastic (MPs) pollution has emerged as a critical environmental stressor with growing implications for freshwater ecosystems. This study investigates the sub-lethal toxicological effects of polystyrene (PS-MPs) and polyethylene microplastics (PE-MPs) on Oreochromis mossambicus under controlled laboratory conditions. Acute toxicity tests established the 96-h LC sub(50) values, identifying PE-MPs as significantly more toxic than PS-MPs. Sub-lethal concentrations-15.33, 30.66, and 76.34 mg/L for PE-MPs and 50, 250, and 500 mg/L for PS-MPs-were selected based on the LC sub(50) values and applied in a 14-day semi-static exposure set-up. Tissue-specific MPs accumulation analysis revealed a dose-dependent retention of MPs in gill, gastrointestinal, and liver tissues. Biochemical assays indicated significant disruptions in oxidative stress markers and metabolic enzymes. Significant increases in catalase (CAT), superoxide dismutase (SOD), and thiobarbituric acid reactive substances (TBARS) levels were observed, along with alterations in alanine aminotransferase (ALT), alkaline phosphatase (ALP), and essential macromolecules (proteins, carbohydrates), indicating oxidative and metabolic stress. Genotoxicity, assessed by the micronucleus assay, demonstrated a concentration-dependent increase in micronucleated erythrocytes, indicative of chromosomal damage. Histopathological evaluations of gill and intestinal tissues revealed MPs-induced structural alterations, supporting the observed altered biochemical and genotoxic responses. These findings offer mechanistic insights into the sub-lethal toxicity of MPs, highlighting their potential to induce oxidative imbalance, genotoxicity, and histoarchitectural damage in tilapia. The study underscores the urgent need for comprehensive risk assessments and mitigation strategies to address microplastic contamination in inland aquatic systems.