Physicochemical Alterations of LDPE Microplastics During Simulated Gastrointestinal Digestion

Microplastics (MPs) are widespread environmental contaminants that are increasingly detected in food chains and human tissues. While traditionally considered chemically inert, recent studies suggest that MPs may undergo surface and chemical transformations upon exposure to physiological environments. The human gastrointestinal (GI) tract presents dynamic conditions, including enzymatic activity, pH shifts, bile salts, and microbial interactions, which can modify the structure and behavior of MPs. These digestion-related transformations may influence MPs' bioavailability, toxicity, and ability to interact with biological systems.

This study investigated the surface-level transformations and chemical composition of low-density polyethylene (LDPE), a polymer commonly found in food packaging, during simulated gastrointestinal digestion. LDPE samples were subjected to a standardized in vitro digestion protocol that mimicked oral, gastric, and intestinal phases. Samples were collected at each stage and analyzed using Fourier-transform infrared spectroscopy (FTIR) to assess the surface chemical changes.

The FTIR spectra revealed consistent differences between the virgin and digested LDPE samples. The digested samples exhibited lower overall transmittance, suggesting surface alterations. The reduction in the intensity of the CH₂ rocking peak (~719 cm⁻¹) indicated a potential decrease in crystallinity. The methyl group peak (~1379 cm⁻¹) was absent, and the CH₂ bending region (~1460 cm⁻¹) showed slight shifts and intensity changes, possibly linked to the degradation or structural rearrangement of the polymer chain. Additionally, a new band appeared at approximately 2070 cm⁻¹ in the oral and gastric phases, which may be associated with degradation products or contaminant residues.

These findings demonstrate that gastrointestinal conditions can alter the physicochemical properties of LDPE microplastics, particularly at the surface level. Such modifications could enhance their ability to adsorb or transport toxic substances, potentially increasing biological interactions and health risks. Understanding these transformations is critical for the accurate toxicological risk assessment of ingested MPs.