PET micro/nanoplastic exposure alters the physicochemical fingerprint of epirubicin-albumin mixtures and modulates bacterial growth and stress responses in Escherichia coli and Staphylococcus aureus.

Polyethylene terephthalate micro/nanoplastics (PET MNPs) may alter the measured physicochemical behavior of drug-protein formulations. This study examined whether PET MNP exposure produced differences in epirubicin (EPI)-bovine serum albumin (BSA) formulations and in bacterial responses to their 0.2 µm filtrates. Formulations containing 1, 10, or 100 µM EPI and 2.5 mg mL BSA were evaluated with 0, 50, 250, or 750 µg mL PET MNPs using fluorescence and UV-vis spectroscopy, dynamic light scattering, zeta-potential analysis, Rayleigh scattering, reactive oxygen species measurements, and protein-stability assays. Empirical modeling of intrinsic BSA fluorescence yielded higher but imprecisely estimated point estimates for the 50 and 250 µg mL PET formulations than for the PET-free formulation, consistent with right-shifted fluorescence-response profiles. Broad bootstrap intervals indicated limited parameter identifiability. The non-monotonic response at 750 µg mL PET was not assigned to a numerical parameter. was interpreted as a descriptive response parameter rather than a thermodynamic binding constant. UV-vis-based estimation showed a graded reduction in apparent EPI-equivalent response with increasing PET exposure in formulations prepared without BSA, whereas the response remained comparatively stable in BSA-containing formulations. These estimates describe differences in detectable EPI optical response and do not directly quantify free EPI. Complementary measurements identified formulation-dependent differences in fluorescence, absorbance, apparent hydrodynamic populations, surface charge, scattering, and oxidative responses without evidence of extensive bulk protein denaturation. The filtrates produced species- and formulation-dependent effects on bacterial growth and stress-related endpoints in and . Collectively, prior PET MNP exposure was associated with changes in the physicochemical fingerprint of EPI-BSA formulations and bacterial responses to their filtrates. However, free EPI was not independently quantified, and contributions from filter-passing PET species or leachable constituents could not be excluded. The findings therefore do not establish binding stoichiometry, thermodynamic affinity, competitive displacement, or redistribution of EPI among aqueous, albumin-associated, and particle-associated fractions.