Aging of microplastics and their role as vector for copper in aqueous solution

• Aging alters physical and chemical properties of microplastics. • Aging enhanced the adsorption of copper ions on mPA and mPET. • Adsorption capacity of copper on MPs was maximum at the solution pH = 10. Microplastics (MPs), considered to be potential vectors for the transfer of heavy metals, undergo aging in the environment. However, the aging mechanisms of MPs and their interactions with heavy metals in aquatic environments still require additional studies. This study investigated the aging of micro-sized polyethylene terephthalate (mPET) and polyamide (mPA) in simulated seawater and changes in their physical and chemical properties, as well as the adsorption of copper by virgin and aged MPs. The effect of pH on adsorption behavior of MPs on copper was also elucidated. The results showed that the aging process of MPs was characterized by some wrinkles along with rough and fractured surface textures, as well as the changes in functional groups such as hydroxyl groups (–OH), aromatic carbon–carbon double bond (C C), and carbon hydrogen bond (C-H). These changes further influence the aromaticity of the aged MPs and their affinity to pollutants. The aged MPs have higher sorption abilities as compared with that of virgin MPs (e.g., aged mPA > aged mPET > virgin mPA > virgin mPET) and the maximum adsorption capacity of mPA and mPET was achieved at pH 10. This study would contribute to understand the interactions among aged MPs, copper, and environmental factors, which can serve as a baseline for further studies on the toxicity of MPs in combination with heavy metals in the environment.