Dissecting Microplastics Stress: Impacts of Type, Size, and Dose on Nutrient Cycling, Growth, and Antioxidant Defense System in Maize Plant

Microplastics are emerging contaminants in agricultural systems, yet the toxic effects of polymer type, particle size, and application rate on plant growth and physiology remain poorly understood. This study examined the effects of three microplastic types (polyester, polyethylene, and nylon), across three size classes (< 0.212 μm, 0.212–1 μm, and 1–5 μm), and at three dosage levels (0.1, 1, and 10 mg L−1). Results revealed significant (P < 0.05) growth inhibition, with the minimum (50.49 ± 0.56 cm) in polyethylene application at 10 mg L−1 having size < 0.212 μm and the maximum plant height (71.89 ± 4.76 cm) in the control. Root fresh weight declined by 25–32% under microplastics exposure, with nylon exhibiting the least adverse effects. Antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, showed increased activities under microplastic stress, with the order of response being polyethylene > polyester > nylon. The highest enzymatic response was observed with polyethylene at 10 mg L−1 and lowest size, which increased superoxide dismutase, peroxidase, and catalase activities to 121%, 125%, and 123%, respectively, compared to control (72.96 ± 6.86, 61.84 ± 4.16, and 43.20 ± 3.65 units g−1 respectively). Nylon induced the lowest response of enzymetic activity. These findings demonstrate that microplastics types, sizes, and concentration critically influence maize growth and stress physiology, with polyethylene and polyester posing greater risks than nylon. The study shows that the potential threat of microplastics to agricultural productivity and highlights the need for further research into their mechanisms of action and mitigation strategies in agroecosystems.