Microplastics are produced when plastic breaks down in landfills and is exposed to UV light in the sun. Certain parts are so minute that they are measured in nanometers (a billionth of a meter). They can be taken into neighboring waterways or blown about by the wind. Despite rising plastic consumption, they are increasingly ubiquitous in the environment.
According to University of New Mexico researchers, significant amounts of microplastics have been found in the testicular tissue of both humans and dogs. This finding raises more concerns over the potential impact of microplastics on human reproductive health.
In a recent investigation, scientists discovered 12 different microplastics in the testes of 23 people and 47 dogs.
According to their research, all tests in dogs and humans have microplastics. Using a unique analytical method, the team also quantified the number of microplastics in the tissue samples and found associations between specific forms of plastic and lower sperm counts in the canine samples.
Xiaozhong “John” Yu, MD, PhD, MPH, UNM College of Nursing, said, “Heavy metals, pesticides, and endocrine-disrupting chemicals have all been implicated in a global decline in sperm count and quality in recent years.”
After speaking with his colleague Matthew Campen, PhD, a professor at the UNM College of Pharmacy who has found microplastics in human placentas, he wondered if there might be another factor at play.
Yu said, “Have you considered why there is this decline (in reproductive potential) more recently? There must be something new.”
This prompted Yu to plan a study utilizing the identical experimental setup that Campen’s lab had employed for the placenta investigation.
The New Mexico Office of the Medical Investigator, which gathers tissue after autopsies and keeps it for seven years before discarding it, provided his team with anonymized human tissue. Canine tissue was obtained from private veterinarian clinics offering spay-neuter procedures and animal shelters in the City of Albuquerque.
After chemically dissolving the lipids and proteins from the samples, the scientists spun each in an ultracentrifuge, leaving a plastic nugget at the tube’s bottom. The plastic pellet was heated to 600 degrees Celsius in a metal cup. Using a mass spectrometer, they examined gas emissions when different kinds of plastic were produced.
A microgram is one-millionth of a gram, and the average concentration of microplastics in canine testicular tissue was found to be 122.63 micrograms per gram of tissue. The average concentration in human tissue was 329.44 micrograms per gram, which is considerably more significant than the average value Campen reported in placental tissue and almost three times higher than that in dogs.
Yu said, “At the beginning, I doubted whether microplastics could penetrate the reproductive system. I was surprised when I first received the results for dogs, and I was even more surprised when I received the results for humans.”
Scientists discovered that polyethylene (PE), the polymer used to produce plastic bottles and bags, is the most common polymer in human and canine tissues. PVC, utilized for many different purposes, such as residential, municipal, and industrial plumbing, came next in dogs.
According to Yu, higher amounts of PVC in the tissue were linked with a lower sperm count. However, the research could only count the sperm in the canine samples—not the human ones, which had been chemically preserved. There was no association with the PE content in the tissue.
Yu said, “The plastic makes a difference—what type of plastic might be correlated with potential function. PVC can release many chemicals that interfere with spermatogenesis and contains chemicals that cause endocrine disruption.”
Dogs and humans share an environment and coexist, which is one reason the study studied the tissue of the two species. They also have certain biological traits in common.
He claimed that dogs are more closely related to humans than rats and animals. “Their spermatogenesis and concentration are more similar to humans in terms of physical characteristics.” He continued, “Canine sperm counts also appear to be declining.” “We think that environmental factors that are common to both humans and dogs are contributing to their decline.”
Yu noted that the average age of the men in the OMI autopsy samples was 35, meaning their plastic exposure began decades ago when there was less plastic in circulation. “The impact on the younger generation might be more concerning now that there is more plastic than ever in the environment.”
The findings point the way for additional research to understand how microplastics might affect sperm production in the testes, he said. “We have a lot of unknowns. We need to really look at the potential long-term effects. Are microplastics one of the factors contributing to this decline?”
Journal Reference:
- Chelin Jamie Hu, Marcus A Garcia, Alexander Nihart, Rui Liu, Lei Yin, Natalie Adolphi, Daniel F Gallego, Huining Kang, Matthew J Campen, Xiaozhong Yu. Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis. Toxicological Sciences. DOI: 10.1093/toxsci/kfae060