Microplastic-induced changes in Cd and Cr behavior in the agricultural soil-wheat system: Insights into metal bioavailability and phytotoxicity

Microplastics (MPs) and heavy metals widely coexist in agricultural soils, posing significant risks to soil-plant ecosystems. This study explores the effects of five common MPs—polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polylactic acid (PLA)—and environmental-simulating microplastics (EMPs), composed based on the composition of local MPs in agricultural soils, on the bioavailability and phytotoxicity of Cd and Cr in soils. Pot experiments demonstrated that MPs, particularly PE and EMPs at a 5% dosage, markedly decreased soil pH, water-holding capacity, and soil organic carbon content. This decrease in pH led to enhanced Cd and Cr mobility and bioavailability, especially with PE and EMPs increasing Cr bioavailability in 15 cm depth soil by up to 43.9% and 37.8%, respectively. In soils with 2.1 mg/kg of Cd and 390 mg/kg of Cr, both 1% and 5% doses of MPs inhibited wheat growth while enhancing the uptake and translocation of Cd and Cr in wheat. Notably, PE, PS, PLA, and EMPs exposure significantly elevated levels of oxidative stress markers (SOD, POD, CAT, and MDA) in wheat. These findings highlight the importance of further research on the combined impacts of MPs and heavy metals on soil health and plant safety.