The role of Tenebrio molitor L. (Coleoptera: Tenebrionidae) in transforming waste by biodegradation of polystyrene foam and its environmental implications.

The accumulation of non-biodegradable plastic waste constitutes a persistent environmental threat. Certain insect larvae may consume plastic waste; however, the environmental destiny and soil biodegradation kinetics of their resulting frass are not well characterized. This study examined Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) larvae's ability to consume 2 polystyrene foams, extruded (XPS, plate-type) and expanded (EPS, packaging-type), over a 5-week period, and evaluated how foam type and bran supplementation influenced polymer depolymerization and the decomposition behavior of the resulting frass during soil incubation. On a pure foam diet, larval plastic intake peaked during the second week, reaching 6.54 mg for EPS and 4.64 mg for XPS, corresponds to consumption rates of 0.01 to 0.05 mg larva-1 day-1. Bran addition increased foam consumption, preserved larval biomass, and hastens frass decomposition. Soil incubation experiments revealed that frass from the bran-supplemented EPS treatment achieved 100% cumulative mass loss in 12 days, whereas pure XPS-derived frass took up to 18 days. ATR-FTIR analysis revealed oxidative modifications to the polymer structure, whereas gel permeation chromatography revealed reductions in weight-average molecular weight (Mw) of 52.9% for EPS and 27.8% for XPS, accompanied by increased polydispersity index (PDI), confirming polymer depolymerization. Furthermore, the z-average molecular weight (Mz) of EPS and XPS fell by 39.5% and 20.4%, respectively, showing that EPS depolymerized more extensively. Overall, foam type and bran supplementation, along with their interaction, significantly impacted larval performance, polymer depolymerization, and the behavior of insect-derived frass decomposition, highlighting how these factors influence the polymer breakdown and decomposition process during soil incubation.