Assessing the effects of polyethylene microplastic aging on the sorption of pyrene via simulated sunlight irradiation

The sorption and transport of environmental pollutants with microplastics (MPs) is a growing environmental concern due to the increased use and emissions of MPs and their high affinity toward many organic contaminants. This study examines the impacts of environmental aging of high-density polyethylene (HDPE) via sunlight irradiation on its molecular interactions with pyrene, a model hydrophobic organic pollutant. HDPE MPs were artificially aged under simulated sunlight irradiation for different exposure times. During aging treatments with simulated sunlight irradiation, morphological changes, such as cracks and rough surfaces, were induced on the HDPE particles; however, destructive oxidation was not observed. Batch sorption experiments were conducted on the aged and pristine MPs. Results reveal that pyrene sorption on MPs was enhanced for the aged HDPE particles and the sorption increases with increased irradiation time, indicating that aged HDPE has a higher sorption capacity than the pristine one. These results are attributed to the physical alteration in HDPE, which increases the surface area and promotes aqueous pyrene sorption on MPs. These results provide possible mechanistic explanations for the accumulation of hydrophobic organic pollutants with MPs in aquatic environments.