Photodegradation remodels plastic carbon pool: Unveiling transformation and fate of particulate, dissolved and gaseous carbon fractions.

As a carbon-based polymer, the production and transportation of plastics exhibit extensive carbon emissions, while the carbon emissions during environmental degradation remain unknown. This study investigates the productions and interdependence of multiple-phase carbon products-particulate organic carbon (POC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and carbon dioxide (CO2) by selecting polypropylene (PP) and poly(butylene adipate-co-terephthalate) (PBAT) plastics under field survey, laboratory UV irradiation and outdoor solar exposure. Photodegradation drove the re-distribution of plastic carbon pools, characterized by concurrent POC loss and DOC, DIC and CO2 production. PP and PBAT exhibit different carbon distribution patterns, which may be due to the combined effects of polymer backbone structure, differences between ester-bond-containing and carbon-chain structures, light absorption capacity, ROS generation ability, and the presence of additives, oligomers, or other leachable components in the commercial materials. An ordinary differential model predicts that the POC of PP and PBAT are entirely dissipated within 581 and 1095 d, finally each unit of plastic will release 53.96 ± 3.53 and 38.55 ± 9.80 g DOC/kg plastic, 1.82 ± 0.30 and 13.52 ± 0.83 g DIC/kg plastic, and 1210.80 ± 8.71 and 313.80 ± 0.79 g CO2/kg plastic, respectively. The findings quantify plastic-derived carbon transformation across the photodegradation of plastics, and highlight their potential role in modulating local and regional biogeochemical cycling.