The increasing amounts of plastic waste, including microplastics (MP), represent a serious global environmental problem due to contamination of the atmosphere, terrestrial and aquatic environments, as well as their potential adverse effects on animal health. Studies have shown that certain types of MP have toxic effects on the reproductive systems of fish, mice, and humans, including reduced fertility, premature puberty, and accelerated aging of reproductive organs. Data on MP exposure and its effects, particularly in mammals, remain limited worldwide, and especially in Croatia, where previous research has primarily focused on aquatic organisms such as plankton, shellfish, and fish. The aim of this project is to develop a biomonitoring method for the detection of MP in animal organs and to investigate the association between MP exposure and earlier onset of sexual maturity. The study will include analysis of MP levels in animal tissues from different habitats: urban, rural, natural, and aquatic environments. Samples will be examined microscopically for the presence of MP, with confirmation using FTIR analysis. Accumulation of MP among different organs will be compared, and the suitability of various animal species as bioindicators of MP pollution will be evaluated. The final outcome will include publicly accessible digital maps containing data on sampling locations and detected MP levels, thereby making the research findings accessible to the wider public and contributing to the assessment of exposure and health risks for animals and humans.