Micro-nanoplastics pollution and mammalian fertility: A systematic review and meta-analysis

Micro: and nanoplastics (MNPs) are fragments derived from physical, chemical, or biological degradation of plastic items. MNPs are one of the main sources of both marine and terrestrial plastic pollution. This study systematically and meta-analytically assesses the reproductive toxicity in mammals of key plastic components found in MNPs, focusing on polystyrene (PS), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). PubMed, Medline, and CAB Abstracts databases were used to identify the relevant scientific papers, and 79 articles were selected for the systematic review. Six articles included two different species, and 19 papers contained both in vivo and in vitro studies, resulting in a total of 102 experiments being considered and analysed in the meta-analysis. Interest in the reproductive toxicity of MNPs in mammals has increased, peaking in the last two years. Five species (rat, mouse, bovine, pig, and human) have been studied, with most experiments carried out in vivo in mice, focusing on male fertility. The most studied plastic polymer is PS, and both micro- and nanoparticles were tested at single or multiple concentrations. Toxic effects are documented across various species, particle size, and polymer type. A pronounced concentrationdependent toxicity has been observed, particularly at high concentrations/doses of MNPs. There is a gap in research on food-producing animals, which are both relevant models for human health and potential vectors for MNPs into the human food supply chain. Overall, these findings emphasizpe the importance of continued research to elucidate the pathways and mechanisms through which MNPs impact mammalian reproductive health, ultimately advancing our understanding of how these pervasive pollutants interact with biological systems across diverse species.