Photochemical\nOxidation of Polyethylene Terephthalate\nMicroplastics Adsorbed on Sand and Silica Surfaces

The environmental contamination by plastics, microplastics,\nand\nrelated compounds is a major concern. While the detection and release\nof micro- and nanoparticles from these materials have been widely\nstudied, the formation and release of molecules resulting from their\ndegradation in the environment have been overlooked. This work presents\na study of the products released from poly(ethylene terephthalate)\n(PET) irradiated as pure particles and adsorbed on silica and sand\nsurfaces under different irradiation conditions. The role of oxygen\nwas also evaluated. The products were identified by gas chromatography-mass\nspectrometry (GC-MS) and liquid chromatography-high resolution mass\nspectrometry (LC-HRMS). The main released molecules can be accounted\nfor by considering the cleavage of α- and β-bonds next\nto the ester moiety of the polymer chain. Volatile products such as\nbenzene as well as monomer units of the polymer and related products\nwere identified. In the presence of oxygen, acetic acid and products\nresulting from hydroxylation at the benzenic ring or at the ethyl\nmoiety were detected. Adsorption on silica and sand has little effect\non the photoproduct distributions. The irradiation at 360 nm leads\nto distributions similar to the ones observed at 257 nm, but the reaction\nrate is lower. The identified product ethylene terephthalate is a\nmarker of PET plastics and particles and can therefore be used to\nevaluate the environmental contamination by this polymer material.