Study finds microplastics in semen and urine, linking PTFE exposure to lower sperm count

by · News-Medical

Scientists discover that exposure to microplastics, especially PTFE, is associated with lower sperm quality, raising alarms about the impact of environmental pollutants on male fertility.

In a recent study published in the journal eBioMedicine, a group of researchers assessed the presence of multiple microplastics in human semen and urine and their association with sperm quality in a multi-site study across China.

Background 

Microplastics, defined as particles smaller than 5 mm, originate from plastic degradation and are found in various consumer products. These pollutants are widespread in ecosystems and have been detected in multiple human tissues, including the liver, lung, placenta, and semen. Microplastics enter the human body through ingestion, inhalation, or skin absorption. Research indicates daily consumption of microplastics amounts to an average of 5186 ± 3751 particles per kilogram of body weight per year for children and 1482 ± 1072 particles for adults. Studies raise concerns about their effects on human health, especially male reproductive health. The need for further research to better understand the long-term impacts of mixed microplastic exposure on male fertility and to uncover the underlying biological mechanisms is urgent and of paramount importance.

About the study 

To explore microplastic exposure in different regions, male partners attending reproductive medicine centers in three locations were recruited: Henan People's Hospital in Zhengzhou (Henan province) (site 1), Maternal and Child Health Care Hospital of Shandong in Jinan (Shandong province) (site 2), Maternal and Child Health Care Hospital of Xiaogan (Hubei province) (site 3). The study took place between November 2023 and March 2024. Inclusion criteria required participants to be over 18, in a relationship for more than a year without achieving pregnancy, and abstinent for 2-7 days before providing samples. Exclusion criteria included testicular injuries, urogenital inflammation, history of epididymitis, varicocele, and other urological conditions. Among 281 eligible individuals, 113 men aged 24-58 were recruited, with a response rate of 40.2%.

Unexpected microplastic types: In addition to PTFE, microplastics like polyethylene terephthalate (PET) and acrylonitrile butadiene styrene (ABS) were also found, although in smaller percentages, highlighting the variety of microplastic exposure sources.

Participants provided consent, completed questionnaires, and submitted semen and urine samples. Demographic, environmental, and lifestyle factors were collected through one-on-one surveys, and height and weight were measured. The samples were processed in glass containers treated to eliminate potential plastic contamination. Semen analysis followed the World Health Organization (WHO) guidelines, and computer-assisted sperm analysis (CASA) technology was used to measure sperm parameters, including concentration, total count, motility, and morphology.

The study employed Raman micro-spectroscopy to detect microplastic particles in the samples, ensuring rigorous quality control to avoid contamination during collection, transportation, and analysis.

Study results 

Microplastics were detected in both the semen and urine samples of the volunteers. The types of microplastics identified included polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), polycarbonate (PC), and acrylonitrile butadiene styrene (ABS). PS was detected in 100% of the participants, while other microplastics varied in distribution. The participants were exposed to between two and seven types of microplastics, with more than 80% having three to five types detected. Notably, PTFE was detected in 55% of the participants and was found to be significantly associated with reductions in sperm quality.

Impact on sperm quality

Analysis of the relationship between microplastic exposure and semen parameters showed that exposure to PTFE was associated with a reduction in total sperm count (188.90 ± 163.71 million vs. 207.67 ± 132.36 million, p = 0.091) and progressive motility (40.29% ± 19.06 vs. 34.11% ± 17.02, p = 0.083). A dose-response relationship was observed, where an increase in the number of microplastic types led to a significant decrease in total sperm count, progressive motility, and sperm concentration. Participants exposed to six kinds of microplastics had lower total sperm count and progressive motility compared to those exposed to fewer types.

Potential impact of cookware: PTFE, found in non-stick cookware, emerged as the most harmful type of microplastic for male reproductive health, raising concerns about everyday exposure through common household items.

Further analysis using multi-linear regression revealed that PTFE exposure was significantly associated with reductions in total sperm number and sperm concentration after adjusting for confounding factors such as age, BMI, smoking, alcohol consumption, and regional site. The reduction in total sperm count was β = −15.4 (95% CI: −25.6, −5.2), and for sperm concentration, β = −7.2 (95% CI: −12.4, −2.0). Additionally, each increase in microplastic types was linked to further reductions in sperm parameters. PTFE exposure increased the risk of poor semen quality by 4.32-fold in terms of sperm concentration (p = 0.046).

Biological mechanisms

The underlying biological mechanisms are still being investigated, but oxidative stress and the activation of stress-related pathways such as JNK and p38 MAPK are believed to play critical roles in decreasing sperm metabolism-related enzyme activity. Additionally, microplastics are thought to interfere with the synthesis and secretion of testicular steroid hormones, which can impair spermatogenesis. Increased expression of pro-inflammatory molecules, such as NF-κB and interleukins IL-1β and IL-6, has been linked to higher rates of sperm deformity. Furthermore, microplastics may serve as carriers for endocrine-disrupting chemicals, further aggravating reproductive damage.

Cluster analysis grouped participants based on semen quality, showing that those with higher microplastic exposure, particularly to PTFE, had poorer semen quality. A latent category analysis revealed that exposure to more microplastic types was strongly associated with reduced non-progressive motility (p = 0.007).

Conclusions 

To summarize, eight types of microplastics, including PS, PP, PVC, and PTFE, were identified, with most participants exposed to 3-5 types. PTFE exposure was significantly associated with reduced sperm count and motility, showing a dose-response relationship. Participants exposed to 6 microplastic types showed a significant decrease in total sperm number and progressive motility compared to those exposed to fewer types (p = 0.045). Cluster and latent analyses further linked higher microplastic exposure to poorer semen quality. This study highlights the reproductive risks of microplastic contamination and provides critical epidemiological evidence linking exposure to sperm dysfunction.

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