Quantitative Assessment of the Organotropic Distribution of 100–1000 Nm Polystyrene Microparticles in Vivo

Microplastics are considered one of the most significant and ubiquitous pollutants of the biosphere. Health risks to living organisms may be associated with "secondary" microplastics, which are formed from larger polymers under the influence of environmental factors. Microplastic particles are found in all environmental components, as well as in food and drinking water. The increasing production and consumption of polymeric materials leads to an increase in their migration volumes and the risk of impact on human health. Current research convincingly demonstrates that exposure to microplastics can damage cellular structures, develop oxidative stress, activate inflammatory responses, and disrupt epithelial barriers. Accumulation of microplastic particles in organs and tissues can lead to structural and functional changes and also affect metabolic and immune responses. Establishing the relationship between the size and shape of microplastic particles and their biodegradability is important. Most scientific studies described in the available literature focus on assessing the potential toxic effects of microplastic particles. At the same time, data on its biodistribution in various organs are extremely insufficient. Meanwhile, knowledge of the distribution patterns of microplastic particles in the body can contribute to an understanding of the nature and severity of their biological effects. The aim of the study was to quantitatively evaluate the distribution of polystyrene microparticles with diameters of 100, 500, and 1000 nm and their conglomerates in rat organs using heat maps. In a pilot experiment, 12 female rats were divided into 4 groups: a control and three exposure groups (100, 500, and 1000 nm). After 5 hours, cryotomies were performed on the brain, liver, kidneys, lungs, heart, and ovaries, with 4 samples from each animal (12 samples per group). Fluorescence microscopy and subsequent counting of individual particles and conglomerates were performed using the "Microplastic detector" program (Python/OpenCV/NumPy) with an assessment of the density of the objects. The resulting size-dependent organotropy profiles were visualized using heat maps. It was found that individual microplastic particles and their aggregates had different distribution profiles. For particles 100 nm in size, a broader distribution profile of individual particles across organs was observed. However, aggregates of this size demonstrated different distribution dynamics within organs. For particles 500 nm in size, the aggregates were distributed predominantly in kidney and heart tissue. For particles 1000 nm in size, the number of aggregates significantly increased in the liver.