Dose- and Time-Dependent Cytotoxic Effects of Coffee Cup Lid-Derived Polystyrene Microplastics on CHO Cells: A Preliminary in Vitro Study

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Microplastics from everyday plastic products are a growing concern because of their potential biological effects and relevance to human exposure. Although spherical particles are widely used in studies, particles generated from real-world plastic materials may offer a more realistic model of environmental and consumer-related exposure. This study aimed to evaluate the dose- and time-dependent cytotoxic effects of coffee cup lid-derived polystyrene microplastics (PSMPs) on Chinese hamster ovary (CHO) cells. Polystyrene microplastics were produced from coffee cup lids by mechanical processing, followed by homogenization, drying, and suspension in cell culture medium. CHO cells were exposed to microplastic concentrations of 5, 10, 15, 20, 25, 50, 100, 250, 500, and 1000 µg/mL for 24, 48, and 72 hours. Cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the effects of concentration and exposure duration were evaluated statistically. Coffee cup lid-derived PSMPs reduced CHO cell viability in a dose- and time-dependent manner. The IC50 value was not reached within the tested concentration range after 24 h and was therefore reported as >1000 µg/mL, whereas the estimated IC50 values were approximately 250 µg/mL after 48 h and approximately 94.4 µg/mL after 72 h. Prolonged exposure resulted in a pronounced reduction in cell viability, particularly at higher concentrations. These results suggest that PSMPs obtained from daily-use coffee cup lids may produce increasingly pronounced cytotoxic responses under prolonged in vitro exposure. However, further studies incorporating particle characterization, additional mechanistic endpoints, and human-relevant cell models are needed to clarify the biological significance of these findings.