Microplastics have been found in the testicles of men and dogs
US medical researchers have conducted a first-of-its-kind study in which they examined the prevalence of microplastics and their levels in the testes of men and dogs using advanced pyrolytic gas chromatography. The results are not encouraging - according to the authors, the ubiquitous presence of microplastics may be contributing to the decline in male fertility.
The trend of declining sperm count and quality in men, along with the increasing prevalence of testicular dysgenesis syndrome, has long concerned experts. They continue to look for possible causes, including environmental factors such as exposure to plastic particles less than five millimetres in diameter and their entry into the circulatory system.
Despite the interest in the topic, there is not much data on the impact of microplastics on the human reproductive system. New information was obtained by a team of doctors from the University of New Mexico (USA), whose article was published in the journal Toxicological Sciences. The researchers aimed to quantify the prevalence and composition of microplastic in the testes - not just of men, but also of male dogs.
"Addressing the gaps [in knowledge] is critical to fully understand the potential risks posed by microplastics. Companion animals face similar anthropogenic environmental contaminants. In addition, dogs share similarities with humans in terms of spermatogenesis and hormonal signalling pathways. These similarities emphasise the decreased sperm count and motility observed in both species in different regions, practically making dogs 'bioindicators' of environmental exposures," explained the authors of the new work.
Using pyrolytic gas chromatography-mass spectrometry (Py-GC/MS), the medics identified and characterised 12 types of micro- and nanoplastics contained in 47 dog testicular samples and 23 human samples. The material for the study was formalin-stored testes from deceased men who were between 16 and 88 years old at the time of death. The dogs' reproductive organs were donated by veterinary clinics from Albuquerque that performed the castration procedure. Specialists took into account the health condition, sex, age, breed and type of nutrition of the animals, and analysed the number of sperm.
Microplastics were found in all samples, emphasised the authors of the article. The list included polyethylene, polyvinyl chloride (PVC), nylon 66 (polyamide 66), nylon 6, butadiene styrene rubber, polyurethane, polypropylene, polymethyl methacrylate, acrylonitrile butadiene styrene (ABS plastic), polyethylene terephthalate, polycarbonate and polystyrene. However, their levels varied significantly, from a minimum concentration of 2.36 micrograms per gram of tissue studied to the highest concentration of 485.77 micrograms per gram. The average was 122.63 micrograms per gram in dogs and 328.44 micrograms per gram in humans (i.e. 2.67 times higher).
Polyethylene, polyvinyl chloride, and ABS plastic (in humans) were predominant in the percentage of samples from both groups. The breed and age of the dogs did not affect the concentrations of microplastics in the testes, but it was possible to detect a correlation between the weight of the testes and the content of PVC and PET. In addition, particle levels were higher in animals operated on in public shelters rather than in private clinics. Sperm counts decreased significantly as the concentrations of ABS plastic and polystyrene increased.
As for humans, in their case, lower concentrations of microplastic were found in those over 55 years of age. According to the scientists, this can be explained by unique physiological and biological processes, in particular spermatogenesis and age-related changes in the seminal tubules. For example, the constant renewal and release of sperm during spermatogenesis likely contributes to the regular removal of plastic particles from the seminal tubules, reducing overall levels of such "contamination" over time.
"Our results showed how ubiquitous microplastics are in the reproductive system of both dogs and humans. This could have global implications for male fertility in the future. The association between levels of certain polymers and normalised testicular weight suggests a role for microplastics in the observed decline in sperm count and quality," the medics stressed.
They called for follow-up studies on a larger sample to raise awareness of the possible harmful effects of microplastics and to take measures to protect men's reproductive health.