Uptake, translocation, and phytotoxic mechanisms of polystyrene and polylactic acid nanoplastics in tobacco seedlings.

Nanoplastics (NPs) are increasingly recognized as pollutants in agricultural systems, yet their impacts on tobacco remain poorly understood. This study systematically investigated the uptake, translocation, and physiological responses of tobacco seedlings exposed to polystyrene (PS, 50 nm) and polylactic acid (PLA, 50 nm) NPs under hydroponic conditions. Both PS and PLA exhibited concentration-dependent effects. Low concentrations (10 mg L-1) moderately enhanced biomass accumulation (8.2-24.4%) and photosynthetic performance (21.6-33.5%), whereas high concentrations (100 mg L-1) significantly suppressed growth (9.4-30.2%), reduced chlorophyll content (6.0-14.9%), decreased photosystem II efficiency, and increased lipid peroxidation. Confocal microscopy revealed the presence of fluorescently labeled NPs in roots, stems, and leaves, indicating their uptake and translocation within tobacco seedlings. FTIR analysis detected characteristic PS (698 cm-1) and PLA (1758 cm-1) functional groups in plant tissues and revealed changes in the -OH and C-O-C bands, indicating the occurrence of oxidative stress responses and potential modifications in celluloserelated structures. Overall, the results suggest that NPs adversely affect tobacco growth through integrated mechanisms involving tissue accumulation, redox imbalance, and structural alterations. PLA exerted stronger inhibitory and oxidative effects than PS at the same concentration. These findings advance our understanding of the behavior and phytotoxicity of biodegradable and nonbiodegradable NPs in agricultural environments.