The Effect of Different Aging Methods on the Heavy Metal Adsorption Capacity of Microplastics

Abstract

Microplastic (MP) pollution has emerged as a global concern. MPs undergo aging in the environment, which includes light-induced and temperature-induced degradation. Existing studies on MP aging predominantly focus on UV-induced and high-temperature aging. This experiment addresses the issue of the combined pollution of MPs and heavy metals in the environment, nonbiodegradable polystyrene (PS) MPs and utilizing biodegradable polylactic acid (PLA) MPs along with the heavy metals Cd²⁺, Cu²⁺, Zn²⁺ as the research objects. The study aims to simulate the aging of MPs under UV and high-temperature conditions and to investigate the adsorption of heavy metals (Cd²⁺, Cu²⁺, Zn²⁺) by aged MPs. This research helps to further the understanding of the interactions between MPs and heavy metals in the environment, as well as the environmental risks posed by their combined pollution, thereby providing a foundation for managing MPs and heavy metal contamination. The study reveals that under both aging conditions, the MPs' surface becomes rougher, developing cracks that increase its specific surface area, reduce the average adsorption pore size and zeta potential, and enhance crystallinity and oxygen content. UV aging has a more pronounced effect on the physical and chemical properties of the microplastics. The adsorption level of heavy metals by MPs remain largely unchanged before and after aging; however, the aging process slightly increased the adsorption capacity of the MPs. PS-T increased the adsorption of Cd²⁺, Cu²⁺, and Zn²⁺ by 0.0011, 0.003, 0.002, PS-UV increased the adsorption of Cd²⁺, Cu²⁺, and Zn²⁺ by 0.0024, 0.015, 0.011, PLA-T increased the adsorption of Cd²⁺, Cu²⁺, and Zn²⁺ by 0.0023, 0.014, and 0.023, and PLA-UV increased the adsorption of Cd²⁺, Cu²⁺, and Zn²⁺ by 0.0028, 0.017, and 0.03, respectively.