Micro- and nanoplastics (MNPs) are present in the human body. Small plastic particles have been detected in the central nervous system, blood, heart, testis, semen, placenta, and other tissues. MNP exposure has been associated with disease outcomes such as Inflammatory Bowel Disease, autism spectrum disorder, and cancer, mostly in small sample size studies. In January and early February 2025, two studies investigated MNPs in human brains and potential implications, while two research articles and one review explored effects on female reproduction. Yet another study showed that also “bioplastic” particles are concerning when tested in vivo.
MNPs accumulate in the human brain
Comparing concentrations between different major organs, Alexander J. Nihart from the University of New Mexico Health Sciences, Albuquerque, USA, and co-authors now found MNP levels to be 7-30 times higher in the brain (median of 4917 µg/g) than in the liver (433 µg/g) and kidney (404 µg/g), in a study comprising more than 50 post-mortem samples. In their article published February 3, 2025, in the journal Nature Medicine, they further pointed out that concentrations increased over time, i.e., 4917 µg/g and 3345 µg/g in brain samples from 2024 and 2016, respectively. Notably, levels were even higher in the brains of patients with diagnosed dementia (26,076 µg/g, mean od 12 samples). The authors clarified that “these data are associative and do not establish a causal role for such particles affecting health.” They called for further research to investigate “whether MNPs have a role in neurological disorders or other human health effects.”
For their study, the researchers used decedent samples from 2016 and 2024 in cooperation with the University of New Mexico. They used a combination of pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and visualization methods, which allowed them to assess and capture plastic particles down to the nanoscale of size. This approach does not allow for quantifying the number of particles, but only the mass of all particles present in a sample.
A previous publication had already reported polyethylene (PE) microplastics (MPs) to accumulate in the brain and using a mouse model, found them to induce autism spectrum disorder-like symptoms. Moreover, an in vitro study found microplastics negatively impact human forebrain organoid development.
Haipeng Huang from the Chinese Research Academy of Environmental Sciences, Beijing, China, and co-authors were interested in the mechanism causing brain dysfunction and neurological changes. In their article published January 22, 2025, in the journal Nature Medicine, they described exposing mice to MPs and tracking particle presence and movement through the bloodstream by different imaging techniques.
The researchers reported that circulating MPs are phagocytosed by cells in the bloodstream, and these cells can remain obstructed, leading to a blockage of the cerebral blood vessels. This was further found to lead to lower blood perfusion in the respective vessels, which again caused neurobehavioral disorders. While the scientists investigated exposures over 28 days, “the long-term consequences of … obstruction and the cumulative effects of multiple repeated MPs exposures remain unknown.”
MNPs affect female reproduction.
MNPs have frequently been detected in human placenta, as well as the amniotic fluid, and research has started to explore their impacts on the female reproductive system, but many knowledge gaps still exist. Three articles took a closer look into the impacts on the female reproductive system.
In an article published on December 25, 2024, in the journal Environment International, Qiaoling Wang from Tongji University, Shanghai, China, and co-authors reported the presence of MPs (1-497 µm; 97.7% detection rate) in the follicular fluid of Chinese women undergoing assisted reproductive technology. The higher the MP concentrations, the lower were the fertilization rates. PE was the most abundant polymer type (average of 8.82± 6.14 particles/mL), which is why Wang and co-authors exposed female mice to 20 mg/kg body weight PE particles for four weeks. MP exposure “led to a decrease in the number of oocytes retrieved and fertilization rates while increasing the proportion of poor-quality oocytes.” Given the upregulation of pro-inflammatory gene expression and increased reactive oxygen species, the researchers assumed this to be the causal factor.
Xiu Cheng from Nanchang University, China, and co-authors found NPs to result in multigenerational reproductive toxicity. Their article was published on January 3, 2025, in the journal Ecotoxicology and Environmental Safety. Opposed to Wang et al., Cheng and co-authors exposed female mice not to PE but polystyrene (PS) nanoparticles (NPs) from gestation day 0.5 to 21 days postpartum (30 mg/kg/day). This exposure resulted in a higher incidence of miscarriage and premature birth. The offspring had reduced body weight, disrupted sex hormone levels, and impaired fertility until observed, i.e., 12 weeks after birth. “Overall, these findings indicate that PS-NPs exposure during critical developmental periods impacts ovarian function and reproductive outcomes across generations,” the authors concluded.
Previous research has also found transgenerational effects of maternal PS exposure on male mice, i.e., testicular and hepatic toxicity in offspring.
The outcome of a systematic review on MP impacts on female reproductive health published on January 16, 2025, in the journal Archives of Gynecology and Obstetrics, verifies the findings of the studies by Wang et al. and Cheng et al. Accordingly, MNP exposure has been found to affect ovarian function, decrease fertility, disrupt hormone levels, and impair embryo development. In the review, the author Inam Özem included 15 human and animal experimental studies published between 2021 and 2023 in PubMed, Web of Science, and Scopus. Importantly, many of the included studies “have methodological shortcomings, such as limited data sets and inadequate control groups,“ calling for standardized, carefully designed future research.
Besides the female reproductive system, MNPs also impact male reproduction. For instance, PS MPs have been shown to affect mice testicular development and fertility as well as to cause testicular aging.
“Bioplastic” particles are also toxic
Bio-based and biodegradable plastics are often considered to be a more sustainable alternative to conventional petroleum-based plastics, but they have been shown to have a similar chemical toxicity. Qiancheng Zhao from Peking University First Hospital, Beijing, China, and co-authors now reported that microplastics made of the “bioplastic” polylactic acid (PLA) also have male reproductive toxic effects. Their article was published on January 25, 2025, in ACS Nano. The researchers performed in vitro and in vivo experiments with male mice. They found the PLA MPs to cross and damage the blood−testis barrier and disrupt spermatogenesis, leading to their deformation as well as decreased motility and lower concentrations. In addition, MPs entered the “mitochondrial sheath and disrupted the mitochondrial structure of sperm, causing dose-dependent impairments in mitochondrial function.”
Since June 2021, the European research cluster to understand the health impacts of micro- and nanoplastics (CUSP) includes 71 organizations from 21 countries, focused on improving the understanding of MNPs’ effects on human health. On February 25-26, the outcomes of CUSP will be shared at the final scientific conference.
References
Cheng, X., et al. (2025). “Maternal exposure to polystyrene nanoplastics during gestation and lactation caused fertility decline in female mouse offspring.” Ecotoxicology and Environmental Safety. DOI: 10.1016/j.ecoenv.2024.117632
Huang, H., et al. (2025). “Microplastics in the bloodstream can induce cerebral thrombosis by causing cell obstruction and lead to neurobehavioral abnormalities.” Science Advances. DOI: 10.1126/sciadv.adr8243
Inam, Ö., (2025). “Impact of microplastics on female reproductive health: insights from animal and human experimental studies: a systematic review.” Archives of Gynecology and Obstetrics. DOI: 10.1007/s00404-024-07929-w
Nihart, A. J., et al. (2025). “Bioaccumulation of microplastics in decedent human brains.” Nature Medicine. DOI: 10.1038/s41591-024-03453-1
Wang, Q., et al. (2024). “Polyethylene microplastic exposure adversely affects oocyte quality in human and mouse.” Environment International. DOI: 10.1016/j.envint.2024.109236
Zhao, Q. et al. (2025). “Polylactic Acid Micro/Nanoplastic Exposure Induces Male Reproductive Toxicity by Disrupting Spermatogenesis and Mitochondrial Dysfunction in Mice.” ACS Nano. DOI: 10.1021/acsnano.4c15112
This article was originally published by Lisa Zimmermann at the Food Packaging Forum.
