Promoting LDPE microplastic biodegradability: the combined effects of solar and gamma irradiation on photodegradation

Low-Density Polyethylene (LDPE) is non-biodegradable and breaks down into microplastics (MP) when exposed to sunlight and weathering. This poses a threat to ecosystems, contributing to the micropollutants found in urban treated wastewater. Our study aimed to investigate the effects of solar and gamma irradiation on the biodegradability of LDPE MP. We pretreated them with simulated solar irradiation without (photolysis) and with (photocatalysis) TiO₂ nanoparticles followed by gamma irradiation, leading to the appearance of cracks and roughness on the surface. Simultaneously, thermal stability decreased, and the carbonyl index and crystallinity increased, indicating oxidation and chain scission. Aerobic biodegradability was measured in a static respirometer at 58ºC, using green compost as inoculum, and proved to be effective for screening biodegradability of the pretreated LDPE. The combination of photocatalysis and gamma irradiation produced a synergistic effect on photodegradation, making it the most effective method for promoting biodegradation, revealed by the increased specific oxygen uptake rate (SOUR), which is expressed as millimoles O₂ per mol of carbon per hour, and the greatest biodegradation kinetics constant (k_O2=0.0178 h^-1). The primary mechanism driving biodegradation involved the formation of carbonyl groups, which initiated biological activity.