In an article published on March 22, 2023, in the journal Science of the Total Environment, Qiancheng Zhao from Peking University Third Hospital, Beijing, China, and co-authors investigated the presence of microplastics in human testis and semen. They collected 30 semen and six testis samples from patients in Peking University Third Hospital and analyzed them for microplastic abundance and characteristics by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) and laser direct infrared spectroscopy (LD-IR).
The scientists reported an average abundance of 0.23 micro-sized particles/mL semen and 11.6 particles/g testis. More specifically, by LD-IR plastic particles were detected in 11 semen samples (of up to 2.06 particles/mL semen) and four testis samples. The particles came in various shapes and sizes between 21.76 µm and 286.71 µm. Concerning polymer types, the authors found the majority of microplastics in the testis to be made of polystyrene (PS, 68%) while polyethylene (PE) and polyvinyl chloride (PVC) were the predominant types in semen.
Sperm count has declined significantly over the last decades (FPF reported) and the authors hypothesized that sperm quality deterioration may be linked to microplastic exposure. Chemical pollution in general (FPF reported) and specific compounds in particular (FPF reported) such as endocrine-disrupting chemicals (FPF reported) have been associated with this trend. However, due to their small sample size, Zhao and co-authors could not assess the “potential toxicity mechanisms of microplastic exposure in the male reproductive system.”
Previous studies have demonstrated the reproductive toxicity of microplastics in male mice (FPF reported and here). Microplastics have not only been detected in males but also in the female reproductive system such as the human placenta (FPF reported and here) which can affect the offspring (FPF reported and here).
Eleanor A. Medley and co-authors from the Mailman School of Public Health, New York, USA, performed a systematic review to assess the current scientific knowledge on micro- and nanoplastic translocation across the placental barrier and toxicity on the developing fetus. The article was published on February 27, 2023, in the journal Current Environmental Health Reports. In their literature search, the scientists identified 752 studies of which eleven primary research articles matched their eligibility criteria. The included studies encompass two in vivo animal studies, four studies using in vitro human cell assays, one comprising both in vivo and in vitro, three using ex vivo human placental perfusion models, as well as one observational study in humans.
Nine out of the eleven studies found that small plastic particles cross the placental barrier by using in vitro human cells, in vivo animal, and ex vivo human studies. The reviewed literature “suggests that the placental translocation and toxicity of microplastics and nanoplastics depend on physicochemical properties such as size, charge, and chemical modification.” Studies suggested different mechanisms of translocation, leading the authors to summarize that the mechanism “remains unclear.”
Based on the identified knowledge gaps, Medley and co-authors provide several research needs including (i) the use of particles of various shapes and polymer types (reviewed studies mostly used spherical PS particles), (ii) the consideration of exposure in early pregnancy (reviewed studies mostly reflected exposure during late gestation), and (iii) the investigation “whether maternal exposure to plastic particles is associated with adverse birth and other longer-term developmental outcomes in humans.”
Five Horizon 2020 research projects are now working to better understand micro- and nanoplastic impacts on human health (FPF reported). One of the projects (AURORA) is specifically focusing on the assessment of microplastics’ effects on the placenta and the developing fetus.
References
Zhao, Q. et al. (2023). “Detection and characterization of microplastics in the human testis and semen.” Science of The Total Environment. DOI: 10.1016/j.scitotenv.2023.162713
Medley, A. E. et al. (2023). “A Systematic Review of the Placental Translocation of Micro- and Nanoplastics.” Current Environmental Health Reports. DOI: 10.1007/s40572-023-00391-x
