Study of the combined-carrier dual mechanism of polyethylene terephthalate microplastics and nonylphenol ethoxylates on bovine serum albumin

Microplastics, as carriers of environmental pollutants, may influence their biological effects through adsorption. The adsorption mechanism of polyethylene terephthalate microplastics (PET MPs) on the endocrine disrupting compound nonylphenol ethoxylate (NPE) is studied. Furthermore, the effect of the PET MPs–NPE complex on the structure and function of the carrier protein bovine serum albumin (BSA) is further explored. The adsorption process of PET MPs on NPE conforms to the pseudo-second-order kinetic model (R2 = 0.9985) and Freundlich model (R2 = 0.9241), and belongs to a spontaneous, endothermic, and entropy-increasing process. PET MPs function as effective NPE carriers, achieving a desorption rate of 59.29% in acidic buffer solution (pH 1.2), suggesting that ingestion may enhance NPE release risk in vivo. Multispectral analysis showed that free PET MPs and NPE were bound to Site II of BSA through hydrogen bonding and van der Waals forces, altering BSA’s secondary structure. When PET MPs and NPE coexist, they exhibit a combined effect, manifested by significantly enhanced binding affinity with BSA (Kb from 5.39 × 104 M−1 to 2.71 × 105 M−1) and higher disturbance to BSA conformation than a single component. The PET MPs–NPE complex triggers pronounced conformational changes in BSA, suppresses esterase-like activity, and alters thiol content.