In vivo tracking of Cy5.5-labeled polyethylene microplastics following oral exposure in mice

Microplastics (MPs) are widespread environmental contaminants that pose major health risks; however, their in vivo impact remains unclear. In this study, polyethylene MPs (PE-MPs) were fabricated in two size ranges (1–10 and 10–50 μm) and labeled with cyanine 5.5 (Cy5.5) for fluorescence-based tracking. In simulated digestive fluids, the Cy5.5-labeled MPs maintained their physicochemical properties and exhibited stable fluorescence. In vivo imaging system analysis of both particle sizes administered orally to mice, and examined 7 days after repeated exposure, revealed that the particles remained in the gastrointestinal tract, no detectable fluorescence signal was observed in systemic organs, and were excreted via feces, as evidenced by strong fluorescence signals in fecal samples. The findings differ from our previous study, where prolonged exposure to unlabeled PE-MPs led to lung accumulation. The current results highlight the importance of exposure duration and particle tracking methodology. Our evaluation of MP biodistribution underscores the need to assess long-term exposure and establish effective in vivo tracking techniques. Using Cy5.5-labeled PE-MPs, this study confirmed the reliability of the in vivo tracking approach and demonstrated that short-term oral exposure to PE-MPs results in limited systemic translocation.