Photodegradation of PET plastics produces persistent compounds that accumulate in sediments

Polyethylene terephthalate (PET) is one of the most widely used plastics, particularly in packaging and textiles. Although PET is widely used in consumer products, only 10-28 % is recycled. Most PET waste is not properly managed. It is often landfilled, burned, or simply discarded, eventually making its way into rivers and drainage systems and accumulating in marine ecosystems. In addition to hydrolytic degradation, PET is particularly susceptible to photodegradation, as its UV-absorbing aromatic rings facilitate backbone cleavage and the formation of lower-molecular-weight compounds. While microplastic formation has been widely studied, far less attention has been given to the polar, water-soluble degradation products-despite their potential for high mobility and bioavailability. In this study, PET photodegradation was simulated under controlled marine-like conditions. Using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry, 17 degradation products were identified, five of which confirmed with authentic standards. Laboratory-based simulations indicated that the global annual release of these compounds could range from 1 to 5.5 tons, suggesting potential environmental accumulation. To verify this, targeted environmental analyses were conducted, detecting PET-derived degradation products in marine sediments collected from Ganggu Port, South Korea. This study reveals overlooked polar byproducts of PET photodegradation and highlights their relevance in assessing plastic pollution in marine environments.