ORIGINAL ARTICLE

Microplastic contamination and biochemical stress responses in Lemna minor: a report from Madurai, Tamil Nadu, India

Microplastic contamination in freshwater ecosystems poses an increasing threat to primary producers, initiating toxic cascades that propagate through food webs. Climate-mediated factors including altered precipitation patterns and extreme weather events are likely magnifying microplastic transport and bioavailability. This study assesses microplastic accumulation and associated biochemical stress responses in Lemna minor (Lemnaceae) across four sites in Nallathangal Tank, Madurai, Tamil Nadu, India, a rain-fed urban freshwater body supporting local communities under increasing climate stress. Microplastic concentrations ranged from 0.0068 to 0.0108 g/g plant biomass, with FTIR analysis identifying eight polymer types including acrylonitrile butadiene styrene, polyvinyl chloride, polystyrene, and polycarbonate. Significant biochemical disruption was evident, with markedly elevated catalase activity (F = 8839.633, p < 0.001) and the strongest enzymatic response recorded for malondialdehyde (F = 18337.96, p < 0.001), indicating severe oxidative stress and membrane lipid peroxidation. Concurrent upregulation of peroxidase (F = 254.992, p < 0.001) and superoxide dismutase (F = 280.955, p < 0.001) corroborated activation of cellular antioxidant defence mechanisms. Carbohydrate content (F = 94.67, p < 0.0001) and chlorophyll concentrations (F = 83.75, p < 0.0001) were significantly reduced, indicating impaired photosynthetic efficiency and carbon fixation. Principal Component Analysis explained 88% of total variance (PC1 = 42%, PC2 = 31%, PC3 = 15%), reflecting hierarchical, coordinated stress-response patterns. Correlation analysis revealed strong negative associations between microplastic load and dissolved oxygen (r = −0.765) and dissolved carbon dioxide (r = −0.822). Together, these findings demonstrate that microplastic pollution induces comprehensive physiological disruption in L. minor, threatening ecosystem integrity, primary productivity, and food web stability, and underscore the urgent need for microplastic management strategies in freshwater bodies under combined pollution and climate stress.