IMPACT OF MICROPLASTIC EXPOSURE ON GUT MORPHOLOGY AND PHYSIOLOGY IN FRESHWATER INVERTEBRATES

Abstract

Microplastic (MP) pollution has emerged as a critical ecological threat to freshwater biodiversity, yet its sub-lethal impacts on the internal physiology and gut morphology of aquatic invertebrates remain poorly understood. This study investigates the effects of environmentally relevant concentrations (10, 100, and 1000 MPs/mL) of polystyrene microplastics on gut health in three representative freshwater invertebrates: Daphnia magna, Gammarus pulex, and Chironomus riparius. Using a comprehensive experimental framework that included histological, biochemical, and microbial analyses, we observed significant dose-dependent physiological impairments across all species. Histopathological examination revealed progressive epithelial disruption, with damage scores increasing from a baseline of 0.5–0.7 in controls to 4.3–4.7 under high exposure. Digestive enzyme activity—specifically amylase, lipase, and protease—was significantly suppressed, with amylase activity reduced by over 50% in D. magna. Concurrently, oxidative stress biomarkers showed a marked increase in ROS and MDA levels, while antioxidant defenses (GSH, SOD) were severely depleted, indicating an overwhelmed cellular redox system. Gut wall thickness declined by up to 48%, while Shannon diversity indices revealed significant microbial dysbiosis, with diversity dropping from ~3.8 in controls to below 2.0 in highly exposed groups. Visualizations further supported these findings, with bar plots, scatter plots, and pie charts illustrating the systemic degradation of gut function. Collectively, these results underscore the vulnerability of freshwater invertebrates to chronic MP exposure and highlight the gut as a critical target organ for ecotoxicological assessment. This research provides essential mechanistic insights and baseline data to inform environmental risk assessments and conservation policies aimed at mitigating plastic pollution in freshwater systems.