Sorption of Polybrominated Diphenyl Ethers by Virgin and Aged Microplastics

The sorption kinetics and isothermal sorption of polybrominated diphenyl ethers (PBDEs) by virgin and aged polyethylene (PE) and polystyrene (PS) microplastics with irradiation by ultraviolet light were studied, with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) as a representative compound. The influence of different environmental factors, including salinity and dissolved organic matter, on its sorption were analyzed. The virgin and aged microplastics were characterized by scanning electron microscopy, x-ray diffraction, and total reflection infrared spectroscopy. The different models of kinetics and sorption isotherm were used to fit the data, and the sorption mechanism of PBDEs by microplastics was analyzed. The results showed that the main sorption modes of virgin and aged PE were surface sorption and external liquid film diffusion. The virgin and aged PS presented the surface sorption. The sorption isotherm was consistent with the Freudlich model, indicating that the sorption of BDE-47 by microplastics was characterized by a multi-phase, multi-layer, and non-uniform sorption process. The equilibrium sorption capacities of BDE-47 on virgin PE, aged PE, virgin PS, and aged PS were 3.72, 3.76, 6.04, and 3.46 ng·g-1, respectively. There was no obvious difference in equilibrium sorption capacity between the aged and virgin PE. However, the equilibrium sorption capacity for the aged PS was decreased by 42.38% compared with that of the virgin PS. The partition of the outer liquid membrane diffusion was the main mechanism affecting sorption of PBDEs by PE. Compared with the virgin PS, the increase in crystallinity and surface oxygen-containing functional groups led to a decrease in the equilibrium sorption capacity of PBDEs on the aged PS. The sorption of BDE-47 was not significantly influenced by salinity. However, dissolved organic matter exerted a negative effect on the sorption of BDE-47.