Comparison of the toxic effects of polystyrene and sulfonated polystyrene on wheat under cadmium stress

With advances in plastic resource utilization technologies, polystyrene (PS) and sulfonated polystyrene (SPS) microplastics continue to be produced and retained in environmental media, potentially posing greater environmental risks. These plastics, due to their different physicochemical properties, may have different environmental impacts when compounded with other pollutants. The objective of this study was to investigate the combined toxic effects of PS and SPS on wheat using cadmium (Cd) as a background contaminant. The results demonstrated that Cd significantly impeded the normal growth of wheat by disrupting root development. Both PS and SPS exhibited hormesis at low concentrations and promoted wheat growth. Under combined toxicity, PS reduced oxidative stress and promoted the uptake of essential metal elements in wheat. Additionally, KEGG pathway analysis revealed that PS facilitated the repair of Cd-induced blockage of the TCA cycle and glutathione metabolism. However, high concentrations of SPS in combined toxicity not only enhanced oxidative stress and interfered with the uptake of essential metal elements, but also exacerbated the blocked TCA cycle and interfered with pyrimidine metabolism. These differences are related to the different stability (Zeta potential, Hydrodynamic particle size) of the two microplastics in the aquatic environment and their ability to carry heavy metal ions, especially Cd. The results of this study provide important insights into understanding the effects of microplastics on crops in the context of Cd contamination and their environmental and food safety implications.