Understanding the Fragmentation and Transformation Behavior of Plastics in Marine Environments under the Weathering Effect via Ultrasonication-Assisted Mimicking

As the amount of plastic usage increases, environmentally exposed plastics rapidly accumulate, with a significant portion eventually ending up in the ocean. The fragmentation of plastics has raised considerable concerns regarding microplastics (MPs) as pollutants and potentially toxic substances to ecosystems and human beings. Previous research has highlighted the threat of fragmentation and surface changes caused by eco-corona or weathering, which can result in severe damage to human beings.<br/>Despite the importance of understanding plastic fragmentation, the influence of weathering and the prediction of fragmentation behavior have not been thoroughly investigated. Therefore, it is important to establish an analytical model that can simulate the behavior of environmentally weathered plastics and their transformation. In this study, we focused on the ocean environment, which is considered the ultimate destination for discarded plastics, as our target environment. Our aim is to conduct a comprehensive study on the effects of weathering and the potential threats posed by weathered plastics.<br/>To understand the weathering effect in marine environments, we employed focused ultrasound irradiation. As the cavitation and collapse process repeated during ultrasound irradiation, sonoluminescence emitted ultraviolet (UV) energy to the microplastics. We analyzed the morphological and functional group changes on the surface of particles, comparing manufactured plastic with fragmented nano plastics. Our results showed an oxidation process occurring around the microplastics' surfaces, which we detected through FT-IR and XPS analysis. By comparing the oxidation rate of ultrasound-irradiated microplastics with aged microplastics, we aimed to establish an analytical model for mimicking weathered plastics in marine environments.<br/>While increasing research has highlighted the toxicity of microplastics to the human body, the potential toxicity of naturally fragmented and weathered nano plastics has not been clearly investigated. However, microplastics can transform into nano plastics and undergo changes in surface characteristics due to external physical and biological stresses in the ocean. In this study, we focused on manufactured polyethylene plastic particles and used ultrasound to simulate the natural fragmentation of nano plastic particles caused by weathering in the ocean. We examined the potential threats posed by fragmented nano plastic particles to the human body through immune-cytokine analysis, cytotoxicity tests, and co-culture with human umbilical vein endothelial cells. Our study implemented naturally transformed nano plastics through weathering and evaluated their potential toxicity.