Reproductive toxicity of micro- and nanoplastics: Insights from experimental and human studies

The exponential rise in plastic production has driven widespread contamination by micro- and nanoplastics (MNPs) in the environment. These plastic particles and their chemical additives have been detected in water sources, human bodily fluids, and reproductive tissues. With global fertility rates declining, their role as potential contributors is under investigation. This scoping review compares findings from in vitro experiments, in vivo studies across animal models, and epidemiological data to assess potential reproductive hazards associated with MNP exposure. Forty original studies published within the last decade were identified. MNPs have been detected in human breast milk, placenta, endometrium, ovaries, testis, semen, follicular fluid, blood, and urine samples. Humans are estimated to absorb 74,000-121,000 particles annually through inhalation, ingestion, skin contact, and use of plastic materials, including medical devices. Experimental evidence demonstrates that MNPs can cross biological barriers, interact with cells, and disrupt cellular pathways, including steroidogenesis, energy metabolism, inflammatory pathways, and oxidative stress. Thirty in vivo animal studies have associated MNPs with altered reproductive endpoints in both males (i.e., altered semen quality and spermatogenesis) and females (i.e., altered folliculogenesis, depleted ovarian reserve, and reduced litter sizes), with possible transgenerational effects. In conclusion, current evidence suggests MNPs may represent a reproductive health hazard to humans and animals. The relative contributions of particle toxicity and their chemical additives remain difficult to disentangle. Overall, plastics and their associated chemicals represent a serious health and environmental concern, which continues to grow in the absence of restrictions and international agreements.