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- Role of photooxidation on the abiotic transformation of microplasticsPublication . Sousa, Maria Carolina Melo de; Silva, José Paulo DaPlastic pollution poses a significant threat to terrestrial and aquatic ecosystems worldwide, largely arising from inadequate recycling and waste management practices. This results in the accumulation of microplastics and nanoplastics, which can harm marine organisms and pose potential risks to human health. In this study, polyethylene (PE) and polyethylene terephthalate (PET), two of the most prevalent plastic polymers in circulation, were studied with a focus on their photodegradation in coastal environments, which is a critical abiotic process driven by sunlight radiation exposure. An advanced analytical technique, Liquid Chromatography coupled with High-Resolution Mass Spectrometry (LC-HRMS), was implemented with Atmospheric Pressure Chemical Ionization (APCI) and Electrospray Ionization (ESI) to analyze the released molecules after photooxidation. APCI enhances the detection of moderately polar compounds, whereas ESI provides greater sensitivity for polar compounds containing carboxylic acid functional groups. PET readily degrades and produces a wide range of molecules that are potential environmental contaminants. In contrast, PE is more stable because the absorbance of radiation by its structure is much lower than PET. LC-HRMS allowed the identification of compounds uniquely correlated with each polymer's chemical structure and were therefore considered markers of these polymers in the environment. For PET the identified compounds were benzoic acid (m/z 121.030), terephthalic acid (m/z 165.019), and 4-((2-((4-carboxybenzoyl)oxy)ethoxy)carbonyl)benzoate (m/z 357.062) while for PE, dicarboxylic acids were identified, such as hexadecanedioic acid. Many other compounds were annotated. These results indicate that the identified and annotated compounds are being released from plastics and microplastics and are potential environmental contaminants. On the other hand, by promoting the photochemical reaction on sand surfaces, the presence of microplastics and nanoplastics can be detected, specifically for PET.