Preliminary insights into the photosensensitivity of bio-based plastics: Release of microplastic-derived organic matter in water under UV irradiation.

This is the first study to investigate the possible release of microplastic-derived dissolved organic matter (MP-DOM) in water from three major types of bio-based MPs, namely, polylactic acid (PLA), polyhydroxyalkanoate (PHA) and PLA-PHA mixtures, under ultraviolet (UV) irradiation conditions. At an initial MP concentration of approximately 5 g per liter, the release of MP-DOM from the studied MPs ranged from 1.55 to 6.68 mg of dissolved organic carbon per g of MP after 30 days of exposure. The results from the measured MP-DOM, along with changes in spectral measurements obtained from shortwave infrared spectroradiometer (SWIR) and micro Fourier-transform infrared spectrometer (μFT-IR), confirmed that the bio-based polymers appeared to be photosensitive due to the observed possible formation of carbonyl bonds with increased carbonyl index on the UV-irradiated surface. Additionally, the fluorescence excitation-emission spectra of the MP-DOM revealed narrow fluorescence peaks, suggesting the presence of organic matter with structural features similar to those of humic substances. These findings on bio-based MPs provide insights into their fate and potential impacts on water environments.