Dynamic Uptake and Elimination of Microplastics by Tetrahymena thermophila

Understanding the fate and impacts of microplastics (MPs) on foundational organisms within food webs is essential for accurately assessing their toxicity and environmental risks. While the accumulation and toxicity of MPs in organisms at low trophic levels have been documented, the analysis of the absolute cellular uptake of MPs at a single-cell level with high-throughput methods remains a challenge. In this study, we developed a flow cytometry-based approach integrating a particle balance method and biokinetic modeling to quantitatively assess the uptake and elimination dynamics of fluorescently labeled MPs in the freshwater ciliate Tetrahymena thermophila. The intracellular accumulation of MPs was calculated by subtracting the extracellular MPs from the total exposure amount, ensuring that the measurement was free from interference caused by fluorescence quenching or cellular background noise. Our results revealed that intracellular MPs continuously increased during the first hour, followed by a marked decline within 24 h. By applying a biokinetic model, we demonstrated that the effect of cell division on reducing MP burden is 3.6 to 5.8 times greater than that of elimination, depending on the exposure concentration. The calculated bioconcentration factors (BCFs) exceed 4800, indicating a significant potential for bioaccumulation of MPs in T. thermophila. These results enhance our understanding of the initial processes through which MPs enter the food chain and provide essential technical support for further research on the quantitative toxicity assessment of MP pollution.