Physiological and Biochemical Responses of Tomato (Solanum lycopersicum L.) to Polyethylene Microplastic Exposure

Microplastics (MPs) are emerging environmental pollutants with potential impacts on terrestrial ecosystems and crop productivity. This study examined the effects of polyethylene microplastics (PE-MPs) on the physiological and biochemical responses of tomato ( Solanum lycopersicum L.) plants under controlled greenhouse conditions. A completely randomized design was employed with soil treatments containing 0%, 1%, 3%, and 5% (w/w) MPs, each replicated five times. Tomato seeds were grown in MP-amended soils for six weeks under uniform environmental conditions, after which growth parameters, photosynthetic pigments (chlorophyll a, chlorophyll b, and total chlorophyll), antioxidant enzyme activities (superoxide dismutase, catalase, and peroxidase), and stress biomarkers (malondialdehyde, MDA) were assessed using standard analytical procedures. Increasing MP concentrations significantly reduced plant growth, with shoot height declining from 47.6 cm in the control to 30.1 cm at 5% MPs, root length decreasing from 18.4 cm to 10.7 cm, and dry biomass decreasing from 3.25 g to 1.98 g. Total chlorophyll content declined from 2.56 to 1.51 mg g⁻¹ FW, indicating impaired photosynthetic capacity. In contrast, antioxidant enzyme activities increased markedly, with SOD, CAT, and POD reaching approximately 172%, 165%, and 159% of control levels, respectively, while MDA content increased by approximately 2.3-fold, confirming enhanced lipid peroxidation and oxidative stress. Overall, MPs caused dose-dependent toxicity by disrupting plant growth, impairing photosynthesis, and inducing oxidative stress, highlighting potential risks to crop productivity, soil health, and food security.