Microplastics and human fertility: A comprehensive review of their presence in human samples and reproductive implication.

In recent years, infertility has started to represent a major global public health problem. A growing number of evidences regarding the involvement of environmental factors in the decline of reproductive function have already been highlighted by the specialized literature. Microplastics (MPs) and nanoplastics (NPs) are ubiquitous particles present in all types of ecosystems. They have recently been detected in various human biological samples, including blood, placenta and seminal fluid. This suggests a continuous systemic exposure to this type of pollutant, as well as its capacity to penetrate the key barriers of the human body and trans-generational transfer. The purpose of this work was to critically review the current literature regarding the link between exposure to MPs/NPs and the possible interaction with human infertility. Relevant studies on animal models, as well as the molecular implications and the main access routes of MPs/NPs in the human body, were also highlighted. Studies on animal models have highlighted the toxicity of this type of pollutant manifested through different size-polymer dependent mechanisms of action, including gonadal histological alterations, induction of oxidative stress, cellular apoptosis and hormonal dysfunctions. An integrative perspective on the reproductive risks associated with small-sized polymeric materials is provided. Furthermore, the need to develop standardized methods and protocols for MPs detection in human samples is emphasized, to improve our understanding of the toxic effects on human health and to guide potential preventive or therapeutic strategies for this type of toxicity.