Molecular and Microbial Evidence for Plastic‐Film Transformation in Pig‐Urine‐Derived Media: Distinguishing Aging, Depolymerization, and Biodegradation

Pig urine is a chemically active, microbially populated waste stream containing urea, ammoniacal species, salts, minerals, and dissolved organics. This study experimentally evaluates transformations of low‐density polyethylene (LDPE), polypropylene (PP), and commercial poly(butylene adipate‐co‐terephthalate) (PBAT)/poly(lactic acid) (PLA)‐based film in controlled pig‐urine‐derived media separating hydration, abiotic chemistry, native biological exposure, nonviable‐biomass effects, and enriched biological activity. Experimental endpoints included urine chemistry, mass and thickness changes, tensile properties, ATR‐FTIR, SEM‐EDS, XPS, GPC/SEC molecular‐weight distributions, blank‐corrected LC–MS/GC–MS product screening, microbial‐community analysis, qPCR‐based functional targets, enzyme activities, CO 2 evolution, carbon balance, and leachate ecotoxicity. PBAT/PLA exhibited the strongest ester‐region modification, molecular‐weight reduction, ester‐associated product release, microbial and esterolytic responses, and polymer‐carbon mineralization, reaching 16.0% under enriched exposure. LDPE and PP showed predominantly oxidative aging, moderate chain scission, and limited mineralization. Matched medium‐only, sterile, live, heat‐killed, and consortium‐without‐film controls distinguished polymer‐associated changes from urine, biomass, and microbial background signals. Leachate toxicity was interpreted independently as an environmental‐consequence endpoint rather than evidence of degradation. The control hierarchy strengthened attribution of observed biological and molecular responses across the exposure conditions. Overall, the integrated evidence differentiates physicochemical aging, chain scission, depolymerization, biodegradation, and ecotoxicological consequences, while preventing surface deterioration or background respiration from being misclassified as polymer‐carbon biodegradation.