Microplastics refer to plastic particles and fragments smaller than 5 millimeters in various forms, derived from the breakdown of larger plastics or initially introduced into the environment from the primary constituent particles of plastic. The exact date of the emergence of microplastics in the environment is not precisely known, but it certainly predates the naming of these particles (2004). These particles can enter the bodies of living organisms, including humans, primarily through ingestion and inhalation. Their effects on the body depend on their size, chemical composition, and the composition of substances that later absorb these particles. In this article, we will first briefly examine the classification of these particles in terms of chemical composition and their origins, and then review some evidence of their presence in biological tissues and fluids. Given the increasing production and use of plastics in human life and the fact that most microplastics in nature derive from the breakdown of larger plastics, sometimes several years after their disposal, it is expected that even if plastic production decreases or stops, we will continue to see an increase in their presence in nature for years and decades, leading to human exposure to these compounds (whose effects and consequences of this exposure are not yet fully understood).
