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 in vitro 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-1 BSA were evaluated with 0, 50, 250, or 750 µg mL-1 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 K resp point estimates for the 50 and 250 µg mL-1 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-1 PET was not assigned to a numerical parameter. K resp 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 Escherichia coli and Staphylococcus aureus. 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.