There’s no question plastic pollution is everywhere. Studies have shown that microplastics are lodged in the lungs and bloodstreams of people and animals. Living things breathe in and eat large amounts of plastic microparticles daily. 

And now, a new report reveals that men may have even more to worry about. Researchers at the University of New Mexico have discovered “significant concentrations” of microplastics in the testicles of both dogs and humans.

Researchers say plastic contamination may be exposing men to chemicals that are directly disrupting their reproductive health, which may explain worrying trends revolving around male fertility. Specifically, the study published in Toxicological Sciences uncovered 12 types of microplastics in 47 dogs and 23 human testes.

“Our study revealed the presence of microplastics in all human and canine testes,” reports Dr. Xiaozhong “John” Yu, a professor at the UNM College of Nursing, in a university release.

Yu’s team examined human tissue from the New Mexico Office of the Medical Investigator, which stores tissue from autopsies for up to seven years after a person’s death. The dog tissue samples came from the City of Albuquerque animal shelters and private veterinary clinics that perform spay-neutering procedures.

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After filtering out the fat and proteins from these testicle samples, the researchers made a chilling discovery — an actual “nugget” of plastic at the bottom of their ultracentrifuge. In dogs, there were 122.63 micrograms per gram of tissue. A microgram is a millionth of a gram.

The team found 329.44 micrograms of plastic per gram in human males. That’s nearly three times more than in dogs, and the concentration of plastic contamination was also higher than what scientists found in women’s placental tissue examinations.

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

As for what scientists are finding in the plastics embedded in human testicles, the most prevalent polymer was polyethene (PE) — an ingredient in making plastic bags and bottles. The team also found PVC in dogs, an ingredient in industrial, municipal, and household plumbing materials.

Although they couldn’t conduct the same tests with human sperm, researchers found that sperm counts in dogs were much lower when the samples contained high levels of PVC. Yu notes that they did not see the same connection with PE. Regardless, Yu says it’s undeniable plastic is affecting reproductive health, and dogs could provide a significant red flag for men’s health.

“The plastic makes a difference – what type of plastic might be correlated with potential function,” Yu explains. “PVC can release a lot of chemicals that interfere with spermatogenesis, and it contains chemicals that cause endocrine disruption.”

“Compared to rats and other animals, dogs are closer to humans,” the research adds. “Physically, their spermatogenesis is closer to humans, and their concentration is more similar to that of humans. We believe dogs and humans share common environmental factors contributing to their decline.”

The study notes that the average age of men in the OMI autopsy samples was 35. With that in mind, Yu says this plastic contamination likely began decades earlier, during childhood. This means the trend towards lower sperm counts among men may start long before men even reach adulthood.

“The impact on the younger generation might be more concerning,” Yu warns now that there is more plastic than ever in the environment. “We have a lot of unknowns. We need to really look at the potential long-term effect. Are microplastics one of the factors contributing to this decline?”