Researchers find microplastics in testicular tissue of dogs and humans

Researchers at the University of New Mexico have discovered significant concentrations of microplastics in the testicular tissue of both humans and dogs, adding to growing concerns about their potential effect on human reproductive health.

In a new paper published in the news Toxicological Sciencesa team led by Xiaozhong “John” Yu, MD, Ph.D., MPH, a professor at the UNM College of Nursing, reported finding 12 types of microplastics in 47 dog and 23 human testicles.

“Our study revealed the presence of microplastics in all testicles of humans and dogs,” Yu said. The team was also able to quantify the amount of microplastics in the tissue samples using a new analytical method that revealed correlations between certain types of plastic and reduced sperm counts in the dog samples.

Yu, who studies the impact of various environmental factors on the human reproductive system, said heavy metals, pesticides and endocrine-disrupting chemicals have all been involved in a global decline in sperm count and quality in recent years. A conversation with his colleague Matthew Campen, Ph.D., a professor at the UNM College of Pharmacy who has documented the presence of microplastics in human placentas, led him to wonder if something else might be going on.

“He said, ‘Have you thought about why there is this decline (in reproductive potential) recently? There must be something new,'” Yu said. That led Yu to set up a study using the same experimental method that Campen’s laboratory had used in the placenta study.

His team obtained deidentified human tissue from the New Mexico Office of the Medical Investigator, which collects tissue during autopsies and stores it for seven years before discarding it. The dog tissue came from animal shelters in the city of Albuquerque and private veterinary clinics that perform spay-neuter surgeries.

The team chemically treated the samples to dissolve the fat and proteins and spun each sample in an ultracentrifuge, leaving a clump of plastic at the bottom of a tube. They then heat the plastic pellet in a metal cup to 600 degrees Celsius. They used a mass spectrometer to analyze gas emissions as different types of plastic burned at specific temperatures.

In dogs, the average concentration of microplastics in testicular tissue was 122.63 micrograms per gram of tissue (a microgram is one millionth of a gram). In human tissue, the average concentration was 329.44 micrograms per gram – almost three times higher than in dogs and significantly higher than the average concentration found by Campen in placental tissue.

“At first, I doubted whether microplastics could enter the reproductive system,” Yu said. “When I first received the results for dogs, I was surprised. I was even more surprised when I received the results for humans.”

The researchers found that the most abundant polymer in both human and dog tissue was polyethylene (PE), which is used to make plastic bags and bottles. In dogs, this was followed by PVC, which is used in industrial, municipal and household plumbing and many other applications.

The team was able to count the sperm in the dog samples (but not in the human samples, which had been chemically preserved) and found that higher PVC levels in the tissue correlated with lower sperm counts, Yu said. However, there was no correlation with the tissue concentration of PE.

“The plastic makes a difference: which type of plastic can be correlated with the potential function,” he said. “PVC can release many chemicals that disrupt spermatogenesis and it contains chemicals that disrupt hormone balance.”

The study compared human and dog tissue for a number of reasons, one of which is that dogs live next to humans and share their environment. They also share some biological characteristics.

“Compared to rats and other animals, dogs are closer to people,” he said. “Physically, their spermatogenesis is closer to that of humans and the concentration is more similar to that of humans.” Sperm counts in dogs also appear to be declining, he added. “We believe that dogs and humans share common environmental factors that contribute to their decline.”

Microplastics are created when plastic is exposed to ultraviolet radiation in sunlight and breaks down in landfills. It can be blown around by the wind or transported to nearby waterways, and some pieces are so small they are measured in nanometers (one billionth of a meter). They are now ubiquitous in the environment, even as global plastic use continues to grow. Yu noted that the average age of the men in the OMI autopsy samples was 35 years old, meaning their exposure to plastic began decades ago, when there was less plastic in circulation.

“The impact on the younger generation may be more concerning” with more plastic in the environment than ever, he said.

The findings point the way for additional research to understand how microplastics may affect sperm production in the testicles, he said: “We have a lot of unknowns. We really need to look at what the potential long-term effect is. Are microplastics one of the factors contributing to this decline?”

In spreading his findings, Yu doesn’t want anyone to panic.

“We don’t want to scare people,” he said. “We want to provide the data scientifically and make people aware that there are many microplastics. We can make our own choices to better avoid exposure, change our lifestyle and change our behavior.”