A comparative study of the accumulation of microplastics of different sizes in rat ovaries using an automated quantification algorithm

Introduction. The ovaries are among the key organs of the female reproductive system, responsible for oocyte formation and maturation, as well as the synthesis of sex hormones. Disruptions in these processes, caused by various environmental contaminants, can lead to a range of pathological conditions. Assessing the distribution of plastic microparticles of different sizes is thus critically important for predicting potential reproductive health risks in women.The aim of our study. To determine and compare the characteristics of accumulation of plastic microparticle (100, 500, and 1000 nm) in the ovaries of female Wistar rats following acute systemic administration, using a specially developed software for automated quantitative analysis of fluorescent images.Material and methods. Twelve female Wistar rats were divided into four groups; each group received an intracardiac injection of a 0.5 mL suspension of fluorescent polystyrene microparticles (MP) with diameters: 100, 500, and 1000 nm) or saline (control). Accumulation of microplastic in ovarian tissue was evaluated by fluorescent microscopy with a descriptive approach and a software designed for quantitative assessment of microparticles and their conglomerates. Data were analyzed using the Bootstrap method with Holm–Bonferroni correction; differences were considered significant at p < 0.05.Results. Only occasional background signals were registered in the control group. All experimental groups demonstrated a significant increase in both the number and total area of microparticles compared to control (p < 0.05), with the highest overall accumulation found in the “MP 1000” group. Smaller particles (100 nm) displayed a pronounced tendency to form large conglomerates, whereas 1000 nm particles were primarily present as individual deposits.Limitations. The investigation was limited to examining the distribution of three sizes of plastic MP within a single experimental series and a single animal species (laboratory rats), without accounting for the estrous cycle phase.Conclusion. Even a short-term exposure to plastic MP can result in their accumulation in ovarian tissue, with the location pattern and the likelihood of conglomerate formation depending on the particle size.Compliance with ethical standards. All experiments in this study were conducted in accordance with European Convention standards for the protection of vertebrate animals used for research and other scientific purposes. The study protocol was approved by the local ethics committee (Approval No. 01-02 from February 8, 2024).Contribution: Ryabova Yu.V. – research concept and design, writing the text, preparing figures; Muhammadieva G.F. – conducting the experiment, scientific editing of the text; Valova Ya.V. – research concept and design, data collection and processing; Khmel A.O. – conducting the experiment, data collection and processing; Repina E.F. – research concept and design; Karimov D.O. – research concept and design; Ahmadeev A.R., Khusnutdinova N.Yu., Kudoyarov E.R. – conducting the experiment. All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.Conflict of interest. The authors declare no conflict of interest.Funding. The study was carried out within the framework of the sectoral research program of the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing for 2021–2025.Received: April 4, 2025 / Accepted: October 15, 2025 / Published: April 17, 2026