Extensive HPLC-tandem mass spectrometry characterization of soluble degradation products of biodegradable nanoplastics under environmentally relevant temperature and irradiation conditions

Abstract

Polyester-based plastics, and in particular biodegradable ones, are increasingly used because they may be a partial solution to environmental pollution issues. Therefore, proper identification of their degradation products is strongly needed. In the present work, we optimised a method to investigate the degradation of two biodegradable polymers, polylactic acid (PLA) and polycaprolactone (PCL), together with the non-biodegradable polyethylene terephthalate (PET). We focused the work on nanosize particles (150–200 nm), in relationship with the concern about the presence of nano- and micro-plastics in the environment. We aimed at characterizing the low molecular weight degradation products, which are likely to diffuse and interact with living cells. For this purpose, the polymer samples were aged at 40 or 55 °C under simulated sunlight in a climatic chamber, i.e. in highly controlled conditions, and the resulting liquid phase was analyzed by liquid chromatography coupled to tandem mass spectrometry. The latter technique was used in four different detection modes: single stage mass spectrometry, product ion scan, precursor ion scan and neutral loss. While the first technique has been applied in other works, the unique combination of all these analytical strategies allowed us to show that hydrolysis was the overwhelming degradation pathway for PLA, PCL and even PET. Oligomers ranging between 1 and 8 monomers were identified for PLA and 2 and 8 for PCL. Shorter compounds composed of 1 to 4 units were detected in PET samples. Altogether, the present work reports novel information on the degradation of nanosize plastics and proposes a robust analytical strategy for the extensive characterization of soluble degradation products of plastic material.