Toxicological effects of micro/nano-plastics on human reproductive health: A review

Micro/Nano-plastics (MNPs), including microplastics (MPs; <5 mm) and nanoplastics (NPs; <100 nm), have become pervasive environmental pollutants due to extensive plastic production and insufficient recycling practices. These particles originate from the degradation of larger plastic materials through processes such as photo-oxidation, thermo-oxidation, and incomplete biodegradation, resulting in chemically reactive fragments that persist in air, water, and food. Once released, MNPs enter the human body primarily via ingestion, inhalation, and dermal absorption, ultimately accumulating in various tissues, including reproductive organs. This review provides a comprehensive summary of current knowledge regarding the toxicological effects of MNPs on male and female reproductive health, with a focus on mammalian models and relevance to human exposure. In males, MNPs have been associated with testicular damage, impaired spermatogenesis, reduced sperm count and motility, and disruptions in the hypothalamic-pituitary-gonadal axis. In females, exposure has been linked to altered folliculogenesis, disrupted ovarian hormone levels, impaired oocyte quality, and placental dysfunction. These effects are largely driven by mechanisms involving oxidative stress, inflammation, endocrine disruption, mitochondrial dysfunction, and apoptosis. Furthermore, MNPs have been shown to disrupt gut microbiota composition, contributing to systemic inflammation and reproductive dysfunction through emerging pathways such as the gut-testis axis. Given their widespread presence and multifaceted modes of action, MNPs pose a serious threat to human reproductive health. Therefore, there is an urgent need for stricter environmental regulations, improved waste management, and further research to understand the long-term and transgenerational consequences of MNP exposure.