Research progress on the adsorption and desorption of typical pollutants on microplastics

In recent years, microplastic pollution in the environment has attracted attention worldwide. The large specific surface area and strong adsorption capacity of microplastics lead to interactions with typical environmental contaminants (such as organic pollutants and heavy metals), thereby changing the environmental behavior of these pollutants. It is important to identify the adsorption and desorption processes and mechanisms of organic pollutants and heavy metals on microplastics to better understand the corresponding changes in the environmental behavior and toxic effects of these substances. This paper reviews the adsorption and desorption of organic pollutants and heavy metals by microplastics. The processes and mechanisms of adsorption and desorption of typical pollutants on microplastics are discussed from three aspects:microplastic properties (types, morphology, surface functional groups, polarity, adsorption sites, crystallinity, and aging degree), pollutants properties (surface functional groups, hydrophobicity, polarity, and concentration), and environmental factors (temperature, pH value, salinity, ionic strength, surfactant, and biofilm). The adsorption and desorption of organic pollutants and heavy metals by microplastics are mainly affected by surface adsorption, pore filling, complexation, and hydrophobicity. The adsorption kinetics of microplastics for pollutants mostly conformed to the kinetic (quasi) second-order model, but some conformed to the first-order model. The adsorption isotherms largely conformed to the Freundlich, Langmuir, and Henry models, and some conformed to the linear and composite models. In the future, research on the adsorption and desorption of new pollutants by microplastics should be expanded and the processes and mechanisms of interaction between microplastics and typical pollutants should be further clarified to establish relevant databases and models. This review provides a reference for follow-up research on the adsorption and desorption of typical pollutants by microplastics and a scientific basis for understanding the environmental behavior of microplastics.