Sorption and desorption of 17α-ethinylestradiol (EE2) and β-estradiol (E2) to nylon microparticles

There is growing concern about the environmental impact of microplastics, especially on the transport of organic compounds and pollutants in aquatic systems. To further understand the effect of microplastics on the environmental fate of endocrine disrupting chemicals (EDCs), this study investigated the sorption and desorption of 17α-ethinylestradiol (EE2) and β-estradiol (E2) on polyamide (nylon-12) microparticles. A novel methodology using fluorescence detection was used as a more efficient alternative to chromatographic determination. Equilibrium between the aqueous phase and solid phase concentrations was reached after 24 h of agitation for both estrogens. Freundlich and Langmuir sorption isotherm models fit the data well, suggesting both heterogenous and homogeneous sorption sites for EE2 and E2 on nylon. The sorption capacity for EE2 and E2 was estimated to be 3091.92 and 2920.24 µg/g, while the K_L values were calculated to be 2.35*10^-3 and 2.52*10^-3 L/µg, respectively. The K_F values for the Freundlich isotherms for EE2 and E2 were 51.86 and 58.55 µg/g, and the n values were 1.848 and 1.944, respectively. There was a significant decrease in sorption at increased salinity for E2 (p < 0.05), but not for EE2. The total percent desorption for EE2 and E2 was about 8-9%, which was insignificant compared to initial sorption. The strong sorption and weak desorption of E2 and EE2 on nylon microparticles observed in our study suggest that microplastics, such as nylon, could be a carrier of EDCs in the aquatic ecosystem. This could lead to higher potential bioaccumulation in the aquatic animals and plants, and eventually increase human's EDC exposure and negatively affect human health.