In vitro toxicity from a physical perspective of polyethylene microplastics based on statistical curvature change analysis.

Microplastics which are gradually and randomly decompose into small fragment by exposure of physical and biological external stress are emerging as a significant threat to the all the environments. Here, we have demonstrated the in vitro toxicity of microplastics of two different shapes. To minimize the chemical effect, polyethylene (PE), was used. PE microplastics with two different shapes were prepared, high-density PE microbeads and irregularly ground low-density PE from bulk pellets. It is hypothesized that morphological characteristics and concentration of PE microplastics could affect cellular viability, immunity, and lysis. To quantify the randomness of the microplastic shape, the edge patterns of the generated PE microplastics were converted into numerical values and analyzed using a statistical method. A 10-fold difference in curvature value was observed between microbeads and ground microfragments. To correlate shape differences to toxicology, cells were exposed to PE microplastics on the demand of toxicology studies. We found that the higher concentration and rough structure were associated with the toxicity of plastics toward cells, pro-inflammatory cytokine release, and hemolysis, even though PE is buoyant onto medium. The PE microbeads did not exhibit severe cytotoxicity at any of the tested concentrations, but induced immune and hemolysis responses at high concentrations. When comparing the toxicity of different shapes of PE microplastics, we confirmed by statistical analysis that irregular-shape plastics with sharp edges and higher curvature differences may adversely affect cells, further having possibility to human toxicity in real environment.

In vitro chemical and physical toxicities of polystyrene microfragments in human-derived cells.

With the increase in plastic production, a variety of toxicological studies on microplastics have been conducted as microplastics can be accumulated in the human body and cause unknown disease. However, previous studies have mainly assessed the toxicity of sphere-type microbeads, which may differ from randomly-shaped microplastics in a real environment. Here, we conducted in vitro toxicology analysis for randomly-shaped microplastics based on the hypotheses that (1) physical cytotoxicity is affected by nano-/micro-size roughness in polystyrene (PS) microfragments and (2) chemical toxicity is caused by chemical reagents from microplastics. We confirmed that the PS microfragments increased the acute inflammation of immune cells 20 times than control, the production of reactive oxygen species, and cell death of fibroblasts and cancer cells by releasing chemical reagents. In addition, when the PS microfragments were in direct contact with fibroblasts and red blood cells, the physical stress caused by them resulted in lactose dehydrogenase and hemoglobin release, respectively, due to cell membrane damage and hemolysis. This phenomenon was amplified when the concentration and roughness of the microfragments increased. Moreover, we quantitatively analyzed roughness differences between microplastics, which revealed a strong relationship between the physical damage of cells and the roughness of microplastics.