Advanced Spectroscopic and Thermoanalytical Quantification of LLDPE in Mealworm Frass: A Multitechnique Approach

Plastic pollution, particularly from polyethylene-based materials, poses a major environmental challenge due to their persistence and resistance to degradation. The ingestion of plastics by insects such as Tenebrio molitor (mealworms) has attracted scientific interest as a potential biodegradation pathway. In this study, we present a multitechnique analytical approach for the detection and quantification of linear low-density polyethylene (LLDPE) in insect frass. Frass samples artificially enriched with varying concentrations of LLDPE were analyzed using thermal decomposition coupled with Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry (MS), thermal gravimetric analysis under inert atmosphere, and solid-state ¹³C nuclear magnetic resonance spectroscopy with cross-polarization and magic angle spinning (CP-MAS NMR). Chemometric models based on interval partial least squares (iPLS) were used to improve quantification accuracy. While thermal techniques allowed partial discrimination between frass and plastic degradation profiles, CP-MAS ¹³C NMR provided the highest sensitivity, detecting characteristic polyethylene signals at concentrations as low as 0.096% w/w. This study demonstrates the analytical robustness of CP-MAS NMR and supports its application in future biodegradation assays to quantify plastic residues in biological matrices, thereby contributing to the evaluation of insect-mediated plastic degradation.