Comprehensive assessment of photo-oxidative degradation and biofilm colonization on microplastic pellets in simulated marine environment

Microplastics (MPs) have emerged as a noteworthy environmental concern due to their pervasive presence and potential ecological impact. This study investigates the degradation of three commonly used plastics-polyethylene (PE), polypropylene (PP), and Nylon-6 (N6) under artificial aging conditions mimicking natural sunlight exposure and chemical oxidation in seawater. MP pellets were exposed to varying concentrations of hydrogen peroxide (H₂O₂) in artificially simulated seawater with controlled temperature at 60 °C, 300 RPM agitation, and UV irradiation. The chemical, morphological, and physical changes in the MP pellets over a 160-h period was characterized with Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Field Emission Scanning Electron Microscopy (FE-SEM), Stereomicroscopy, and Particle size analysis (PSA). The results indicate that the degradation patterns and mechanical stability of the plastics varied based on the polymer type and exposure conditions. The PE exhibited significant degradation characterized by the formation of hydroxyl and carbonyl groups along with surface roughening and mechanical instability. The PP showed less degradation compared to PE attributed to its higher melting point and UV stability. The N6 displayed intermediate degradation influenced by amide linkages and mechanical strength. Additionally, this study investigated the formation and characterization of biofilms on MP fragments under simulated marine conditions over a 305-day period. FE-SEM analysis revealed distinct morphologies of biofilm development and Crystal Violet staining quantified the biofilm biomass on the aged PE, PP, N6 pellets. Confocal microscopic analyses using Hoechst-33342 and AO/PI staining further elucidated biofilm composition, highlighting varied microbial densities and cell viability on MP surfaces. These observations contribute to the understanding of the complex processes governing microplastic degradation and emphasize the importance of considering environmental factors in evaluating plastic pollution.