Microplastics (MPs) are ubiquitous in the environment and have a great potential to coexist with metal ions. This work investigated the adsorption–desorption behaviors of three divalent metal ions (Cu, Cd, Pb) on polyamide 6 (PA6) MPs and natural media (riverside soil and marine sediment) and compare their environmental risks. The result showed that the adsorption amounts of metal ions onto PA6 MPs followed the order of Cd(II) (1.210 μmol/g) < Cu(II) (2.299 μmol/g) < Pb(II) (3.756 μmol/g). The adsorption of metal ions on PA6 was significantly affected by water chemistry, including solution pH, salinity, and the concentration of citric acid (CA) and humic acid (HA). Natural water matrices (Yangtze River water and Seawater) enhanced the uptake of three metal ions by PA6 MPs. The analysis of Fourier transform-infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) highlighted the importance of amide groups in controlling the adsorption of metal ions onto PA6 MPs. Site energy distribution indicated that the adsorption of metal ions mainly involved chemisorption. The retention factor (R_f) calculated by the adsorption–desorption behavior of three heavy metal ions indicated that the risk of metal ions posed by PA6 MPs was higher than that of natural media. Among all water matrices, the metal ion/PA6 MPs combinations posed the highest environmental risk in the simulated gastric fluid. This work highlights the behavior of PA6 MPs as metal ions vectors and provides strong evidence the assessment of environmental risk posed by MPs/metal ions combinations, opening new insight into understanding the environmental impacts of MPs.

微塑料（MPs）在环境中无处不在，具有与金属离子共存的巨大潜力。这项工作研究了三种二价金属离子（Cu、Cd、Pb）在聚酰胺 6（PA6）MP 和自然介质（河滨土壤和海洋沉积物）上的吸附-解吸行为，并比较了它们的环境风险。结果表明，PA6 MPs对金属离子的吸附量依次为Cd(II) (1.210 μmol/g) < Cu(II) (2.299 μmol/g) < Pb(II) (3.756 μmol/g)。PA6 对金属离子的吸附受水化学成分的显着影响，包括溶液 pH 值、盐度以及柠檬酸 (CA) 和腐植酸 (HA) 的浓度。天然水基质（长江水和海水）增强了 PA6 MPs 对三种金属离子的吸收。傅里叶变换红外光谱 (FTIR) 和 X 射线光电子能谱 (XPS) 的分析强调了酰胺基团在控制金属离子吸附到 PA6 MP 上的重要性。位点能量分布表明金属离子的吸附主要涉及化学吸附。保留因子 (R _f ) 通过三种重金属离子的吸附-解吸行为计算得出，PA6 MPs 对金属离子的风险高于天然介质。在所有水基质中，金属离子/PA6 MPs 组合在模拟胃液中的环境风险最高。这项工作突出了 PA6 MPs 作为金属离子载体的行为，并为评估 MPs/金属离子组合带来的环境风险提供了强有力的证据，为理解 MPs 的环境影响提供了新的见解。