Polyethylene, whose surface has been modified by UV irradiation, induces cytotoxicity: A comparison with microplastics found in beaches.

Microplastics, plastic particles 5 mm or less in size, are abundant in the environment; hence, the exposure of humans to microplastics is a great concern. Usually, the surface of microplastics found in the environment has undergone degradation by external factors such as ultraviolet rays and water waves. One of the characteristics of changes caused by surface degradation of microplastics is the introduction of oxygen-containing functional groups. Surface degradation alters the physicochemical properties of plastics, suggesting that the biological effects of environmentally degraded plastics may differ from those of pure plastics. However, the biological effects of plastics introduced with oxygen-containing functional groups through degradation are poorly elucidated owing to the lack of a plastic sample that imitates the degradation state of plastics found in the environment. In this study, we investigated the degradation state of microplastics collected from a beach. Next, we degraded a commercially available polyethylene (PE) particles via vacuum ultraviolet (VUV) irradiation and showed that chemical surface state of PE imitates that of microplastics in the environment. We evaluated the cytotoxic effects of degraded PE samples on immune and epithelial cell lines. We found that VUV irradiation was effective in degrading PE within a short period, and concentration-dependent cytotoxicity was induced by degraded PE in all cell lines. Our results indicate that the cytotoxic effect of PE on different cell types depends on the degree of microplastic degradation, which contributes to our understanding of the effects of PE microplastics on humans.

[Mechanisms of Cell Toxicity Caused by Degraded Microplastics].

Microplastics (MPs), defined as plastic particles less than 5 mm in size, are ubiquitous in the environment. The accumulation of MPs in various environmental compartments, such as the ocean, soil, and air, has raised considerable concerns regarding their impact on ecological systems, including marine life and human health. Notably, MPs have been detected in marine organisms such as shellfish and fish, and have even been found in the human body, including in the blood and placenta. Moreover, considering that MPs have been detected in drinking water, human exposure to these particles in daily life is inevitable. To assess the risk posed by MPs to human health, it is essential to consider their physiological and chemical properties, including size, shape, surface modification, and material composition. However, current risk analyses focus primarily on spherical MPs with smooth surfaces, which differ substantially from most of the MPs detected in the environment. Environmental factors, such as ocean waves and ultraviolet radiation, alter the properties of MPs, including size, shape, and surface characteristics. In this review, we summarize current research on MPs, with a particular emphasis on the effects of MP degradation on human health. Furthermore, we generated MPs with surface degradation and evaluated their impact on cell toxicity, along with the underlying biological mechanisms.