The Adsorption and Desorption Behavior of Bisphenol A on Five Microplastics Under Simulated Gastrointestinal Conditions

Microplastics and endocrine-disrupting chemicals (EDCs) are two classes of emerging contaminants, and their compound combination effects pose a health threat to aquatic life. In this study, five types of microplastics with various characteristics, namely polyamide (PA), thermoplastic polyurethane (TPU), polyvinyl chloride (PVC), polyethylene (PE), and polystyrene (PS), were used to adsorb and desorb bisphenol A (BPA) as a closed loop. The adsorption capacity of BPA changed with the microplastic types following the sequence of PA > TPU > PS > PE > PVC, and the desorption capacity decreased in the order of TPU > PA > PS > PE > PVC. The desorption capacity of BPA on microplastics was positively correlated with the adsorption capacity. The sorption kinetic and sorption isotherms of BPA on five microplastics demonstrated that PA and TPU had the maximum adsorption capacities of 57.27 and 47.20 mg/g, which would be attributed to chemical and physical adsorption (chemical adsorption plays a major role), while the adsorption force of PE, PVC, and PS was mainly determined by physical adsorption. Furthermore, on account of the higher adsorption capacity of BPA on TPU and PA, both of them exhibited a higher desorption quantity compared with the three others. The final desorption capacities of TPU and PA in the three solutions were 0.33 ~ 0.36 mg/g and 0.30 ~ 0.36 mg/g. The desorption rates of BPA on microplastics in gastric and intestinal fluids were higher than those in deionized water, but no significant differences existed between them. This study reveals information crucial for understanding the ecological risks of coexisting microplastics and pollutants in the environment.