Regulatory mechanisms of phytotoxicity and corona formation on sprouts by differently charged and sized polystyrene micro/nano-plastics

Abstract

Recent studies have confirmed the biotoxicological effects of micro/nano-plastics (MPs/NPs) and revealed that the physicochemical properties of these particles have essential impacts on toxicity. Nevertheless, the interactions and toxicity mechanisms between MPs/NPs and organisms remain to be systematically explored. This study investigated the phytotoxicity of three polystyrene (PS) particles with different charges and sizes on sprouts and explored the critical role of the physicochemical properties of MPs/NPs on the surface corona. Results indicate that small-sized 0.1 μm positively charged PS (p-0.1 μm-PS) exhibited significant phytotoxicity on day 5, inducing an increase in superoxide dismutase and malondialdehyde and a decrease in catalase of roots, which caused growth deformation, restricted elongation, imbalance in cell viability and metabolic activity, along with a reduction in vitamin C of shoots. Conversely, small-sized 0.1 μm negatively charged PS (n-0.1 μm-PS) manifested phytotoxicity only on day 10, and the toxic effect of large-sized n-2 μm-PS was insignificant. Spectral images revealed that MPs/NPs bound to humic acid-like substances in root exudates, forming particle–corona complexes. The small-sized p-0.1 μm-PS showed the greatest ability to form corona and modulated CO stretching, C–O stretching, and C–H out-of-plane bending vibration. Besides, enhanced adsorption and uptake of small-sized p-0.1 μm-PS were observed in the root epidermis. Overall, these results reveal that positively charged and small-sized MPs/NPs induced stronger phytotoxicity, and enhanced root association and corona formation. These findings provide new perspectives on the toxicity mechanisms and environmental effects of MPs/NPs, thus paving a way for the intensification of research in this field.