Statistical Curvature Change Analysis of Random-Shape Polyethylene Microplastics and their Toxicity from a Physical Perspective

BackgroundMicroplastics,plastics thathave gradually and randomly decomposed into small fragmentsafter exposure to physical and biological external stress,are emerging as a significant environmental threat. They are normally categorized into the following three types: particles, fibers, and random-shape fragments brokendown from bulk plastics. Here, we have demonstrated the in vitro toxicity of microplastics of two different shapes. To minimize the chemical effect, polyethylene (PE),which has abasic chemical polymer structure,was used. PE microplastics withtwo different shapes were prepared,high-density PE (HDPE) microbeads and randomly ground low-density PE (LDPE) from bulk pellets.ResultsTo quantify the randomness of the microplastic shape, the edge patterns of the generated PE microplasticswere converted into numerical values and analyzed using a statistical method. A10-fold difference in curvature value was observed between PE particles and ground PE microfragments. We found that the higher concentration and rough structure were associated with the toxicity of plastics toward immune- or non-immune cells, pro-inflammatory cytokinerelease, and hemolysis, even though PE is buoyant onto medium. The smooth PE particles did not exhibit severe cytotoxicity at any of the tested concentrations, but induced immune and hemolysis responses at high concentrations. ConclusionWhen comparing the toxicity of two different shapes of PE microplastics, we confirmed by statistical analysis that random-shape plastics with sharp edges and higher curvature differences may adversely affect human cells.