New insights into the toxic interactions of polyvinyl chloride microplastics with bovine serum albumin

The binding interaction between emerging pollutant polyvinyl chloride microplastics (PVC MPs) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, resonance scattering spectroscopy (RLS), UV-visible (UV-vis) absorption spectroscopy, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. Fluorescence results revealed that the fluorescence quenching of BSA induced by PVC MPs was originated from the formation of BSA-PVC complex in static quenching mode. According to Stern-Volmer equation, the binding constants (K) between PVC MPs and BSA at different temperatures were obtained, and the number of binding sites was 1.62. The thermodynamic parameters, enthalpy change (ΔH), entropy change (ΔS), and free energy change (ΔG) were calculated to be - 41.77 kJ mol, 43.17 J mol K, and - 54.63 kJ mol via Van't Hoff equation, indicating electrostatic interaction played a key role in the formation of BSA-PVC complex spontaneously. In addition, the alterations of microenvironment and secondary structure in BSA induced by PVC MPs were further confirmed by synchronous fluorescence spectra, UV-vis, FT-IR, and CD. This work not only provides further information for better understanding the binding interaction of PVC MPs with BSA, but also elucidates the potential biological toxicity of MPs at a molecular level.