Adsorption of Endocrine Disruptors onto Polyamide Microplastics: Physicochemical Characterization and Cytotoxicity Assessment

Microplastics represent a growing environmental concern due to their widespread distribution and capacity to sequester hazardous substances. Of particular relevance are endocrine-disrupting chemicals, such as bisphenol A (BPA) and ethinylestradiol (EE2), which pose risks to aquatic life and human health. This study examines how BPA and EE2 interact with polyamide (PA6) microplastics through an integrated assessment involving adsorption kinetics, thermodynamic equilibrium, surface characterization, and evaluation of biological responses using Hep-2 cell models and membrane-mimetic systems formed by POPC lipids. Microplastic samples were incubated with BPA (10⁻⁴ mol L⁻¹) and EE2 (10⁻⁵ mol L⁻¹) solutions, and pollutant uptake was analyzed using various mechanistic models. The pseudo-second-order kinetic approach best described the experimental profiles, indicating chemisorption as the dominant process. Raman spectroscopy analysis identified hydrogen-bonding interactions between the amide functionalities of PA6 and polar groups of both contaminants. Adsorption was optimized at acidic to neutral pH, with pollutant saturation occurring at approximately 90 min for BPA and 30 min for EE2. The Langmuir model provided a superior fit to the equilibrium data, highlighting the preferential formation of a monolayer coverage. Zeta potential measurements confirmed changes in surface charge following pollutant incorporation, while scanning electron microscopy indicated that the structural integrity of the particles remained unaltered. The reduction in cell viability was concentration-dependent and sensitive to particle size, manifesting only at high exposure levels (250–500 mg mL⁻¹) to contaminant-loaded microplastics. Langmuir monolayer isotherm analyses revealed that PA6 induces an expansion of the monolayer's molecular area; when BPA adsorbs onto PA6, the molecular area increases further. Studies using giant unilamellar vesicles (GUVs) demonstrated events such as budding, loss of contrast, and morphological deformation, with these effects being more pronounced in the PA6+BPA system. Collectively, these results establish PA6 microplastics as effective sorbent vectors for compounds with endocrine activity, highlighting their importance as carriers of environmental contaminants with implications for both ecological and human health.

This work was supported by FAPESP (2023/12690-3, 2023/12756-4, and 2021/14235-6), CAPES, and CNPq (302465/2025-1, 407863/2023-0).