Biodegradation of 13C-Labeled and Nonlabeled Aliphatic–Aromatic Polyesters in Compost: Advancing Assessments through Combined Respirometry and Residual Polyester Analysis

Standard polymer biodegradability tests in industrial compost rely on running incubations at high initial polymer concentrations and exclusively determining polymer mineralization to carbon dioxide, while not analyzing the nonmineralized fraction of polymer-added carbon. This work presents an approach that combines the use of 13C-labeled polyesters in compost incubations to selectively track both mineralized and nonmineralized polyester 13C at low initial polyester concentrations with analysis of residual polyester during the incubations by compost solvent extraction coupled to proton nuclear magnetic resonance spectroscopy. Incubations with 13C-labeled poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene sebacate-co-terephthalate) (PBSeT) at low initial concentrations exhibited shorter initial lag-phases and higher relative rates of mineralization as compared to parallel standard incubations run at high initial concentrations of nonlabeled PBAT and PBSeT, suggesting that the latter used polyester amounts in excess of the metabolic capacity of the compost microbial community. Mass balance assessment on polyester-added 13C over the incubations confirmed accurate 13C tracking in both mineralized and nonmineralized pools, despite low initial polyester concentrations. Extraction of residual 13C-labeled and nonlabeled polyesters revealed substantial incorporation of polyester carbon into microbial biomass during compost incubations. Biodegradability tests that exclusively rely on mineralization measurements may therefore underestimate polymer biodegradation in compost.