Sorption and bioacessibility of 17β-Estradiol on Environmental Microplastics: Particle Size, Aging, Competitive Interactions and Co-exposure

Microplastics (MPs) have been extensively studied in aquatic environments due to their potential to act as vectors for emerging contaminants. This study investigated the sorption of the natural hormone 17β-estradiol (E2) onto polyethylene terephthalate (PET) and polyethylene (PE) MPs, considering particle size and aging effect over sorption capacity and toxicity of co-exposure. MPs were obtained from plastics collected from the Monjolinho River in São Paulo, Brazil, and ground into different size fractions. Additionally, artificial aging was simulated by exposing PET samples to ultraviolet (UV) radiation (254 nm, 16W) for 45 days, and co-exposure with bisphenol A (BPA) was also assessed. To evaluate the potential toxicity of E2 and environmental MPs, a cell viability assay (MTT) was performed using zebrafish (Danio rerio) hepatocytes (ZF-L). The results showed that for PET, the highest sorption occurred in particles ranging from 500 to 1000 µm, while for PE, the highest adsorption was observed in particles between 350 and 500. Particles smaller than 125 µm exhibited low sorption, likely due to their tendency to aggregate. Scanning electron microscopy analysis revealed increased surface roughness in artificially aged particles. However, no significant variation in E2 sorption was observed between aged and pristine MPs, indicating that superficial aging did not alter their retention capacity on tested conditions. Furthermore, in the presence of BPA, only this compound was sorbed, suggesting that competitive interactions between contaminants may influence sorption in MPs. The cell viability assay showed no toxicity for E2, MPs, or their co-exposure. These findings highlight the complexity of sorption processes and emphasize the need for further research to better understand how environmental factors influence the bioavailability of emerging contaminants and the risks for aquatic biota.