Researchers have detected microplastics in human testicles.
Volodymyr Zakharov/Getty Images
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Volodymyr Zakharov/Getty Images
Researchers have detected microplastics in human testicles.
Volodymyr Zakharov/Getty Images
Whether it’s our bloodstream, our brains, or our lungs, microscopic fragments of plastic seem to appear every time scientists explore a new part of the human body.
The male reproductive organs are no exception.
New research published this month finds that microplastics can accumulate in the testicles of humans and dogs, raising more questions about the potential health impacts of these particles.
Animal studies have shown that exposure to microplastics can impact sperm quality and male fertility, but scientists are still in the early stages of applying this work to human health.
“Microplastics are everywhere,” says Dr. John Yu, a toxicologist at the University of New Mexico College of Nursing and lead author of the study. “Quantifying these microplastics in humans is the first step to understanding its potential adverse effects.”
When he undertook this study, Yu did not expect that microplastics would penetrate so widely into the male reproductive system, given the tight barrier of blood tissue around these organs. To their surprise, the research team discovered a wide range and high concentration of microplastics in the testicles of about two dozen men and nearly 50 dogs.
The findings may also be relevant to a well-documented global decline in sperm counts and other issues related to male fertility. This trend is linked to a multitude of environmental and lifestyle factors, including certain endocrine disruptors present in plastics.
The growing number of studies like this one are “compelling and should be a wake-up call to policymakers,” says Tracey Woodruff, director of the Center for Environmental Research and Translation for Health at the University of California at San Francisco.
How much and what type of plastic was in the testicles?
This is the largest study to measure the amount of these microplastics that permeate water, food and even the air and end up in the most intimate recesses of male reproductive physiology.
This follows a smaller analysis, published last year by a Chinese team, which detected microplastics in about half a dozen human testicles and in semen.
For the current study, researchers at the University of New Mexico collected testicles from necropsies of people ages 16 to 88 and nearly 50 dogs after they were sterilized at local veterinary clinics.
Dogs can function as “sentinel” animals for disease and exposure to harmful chemicals because they are deeply ingrained in the human environment. Additionally, canine spermatogenesis is more similar to the human process of sperm production than it is to lab rats, Yu says.
Instead of trying to count each microplastic particle, the researchers were able to quantify the total amount of plastic by dissolving all biological tissue and separating the solids.
About 75% of what was left was plastic.
Polyethylene, or PE, made up a large part of it. It is the most used plastic in the world, it is found in packaging, bags and many products.
Matthew Campen, who has examined these tiny particles closely, describes them as “splinter-like and stab-like pieces” because of how “old, brittle and fragmented” they have become.
“We don’t know what they do in the body,” says Campen, a professor at the UNM College of Pharmacy and one of the study’s authors. “Clearly, small, tiny particles can disrupt cell behavior.”
Polyvinyl chloride – what’s found in PVC pipes – emerged as another major culprit and was the second most common microplastic in dogs’ testicles. Vinyl chloride is classified as a carcinogen and long-term exposure, for example in drinking water, may increase the risk of cancer.
Additionally, Yu and his team discovered a correlation between a decrease in the number of sperm in the dog’s testicles and the presence of PVC (the analysis could not be performed on the human samples due to the way they had been preserved).
There is also an association between higher PVC levels and decreased testicular weight. The same thing has been observed with polyethylene terephthalate, or PET, another common source of plastic, which recent research suggests could be harmful.
Woodruff says weight is a somewhat “crude” marker of testicular health effects, although it is frequently used by regulatory agencies to assess the impacts of chemicals.
Consequences ?
The research has many caveats and cannot prove microplastics directly cause male fertility problems. Nonetheless, Yu says the findings are “concerning” and lay the groundwork for more focused studies on the “relationship between microplastic exposure and its potential impact on sperm.”
Emerging evidence suggests that microplastics may have toxic effects on reproductive health.
In a 2022 California state review of evidence, Woodruff and colleagues concluded that microplastics were “suspected” of harming sperm quality and testicular health, but she says that could soon shift from “suspected” to “probable” as more high-quality studies are published.
“In the history of studying chemical or environmental health issues, at the beginning you see these indicators of health harm, and then those that rely on a certain type of evidence tend to grow,” says Woodruff . “I guess we’re just these microplastics are going to cause more harm to health.”
In the University of New Mexico study, the concentration of microplastics in human testicles was on average three times higher than in dogs.
Campen says there are still many unknowns, like what specific concentration would pose a health threat, or how it might vary depending on the type of microplastic or where they accumulate in the body.
“We’re just at the tip of the iceberg,” says Campen, who has used this same technique to quantify microplastic levels in other tissues and organs.
The amount in the testicles is considerably higher than that found in the placenta and that seen in the brain, Yu says.
Exactly how microplastics enter the testicles requires further study. Campen suspects they might hitch a ride through the gut via tiny fat particles that are metabolized and then dispersed throughout the body.
It is plausible that the accumulation of microplastics in the testes may affect reproductive health in several ways. Yu says microplastics could physically disrupt spermatogenesis, disrupt the barrier between the testicles, or carry harmful chemicals.
They could lead to inflammation and cause oxidative stress, which could ultimately affect fertility, says Dr. Sarah Krzastek, a urologist at Virginia Commonwealth University.
“It’s probably another piece of the puzzle that contributes to the decline in male fertility over the years, as these environmental exposures continue to accumulate,” she says. “We don’t yet know the clinical ramifications.”
Richard Lea, a reproductive biologist at the University of Nottingham, calls the findings “alarming.”
“Having something abnormal like that in the testicles is not particularly good news for good reproductive health,” says Léa.
In her lab, Lea has discovered that exposure to phthalates, which are chemicals that can leach from plastics, can reduce sperm’s ability to swim and increase DNA fragmentation in the sperm head. This is likely one of the factors contributing to the decline in sperm quality in domestic dogs in recent decades, a trend that mirrors that seen in humans.
Of course, the testes are only part of the male reproductive system.
Lea says research now shows that these chemical contaminants can affect the hormonal control of reproduction, at different levels of the body, including in the brain.
How to study a ubiquitous substance
Dr. Shanna Swan, a reproductive epidemiologist who has documented the global decline in sperm counts, says she is concerned about the buildup of microplastics. But it’s not yet clear whether finding them in the testicles rather than other parts of the body is more worrisome from a reproductive health perspective.
For example, in her work she has studied how prenatal exposure to endocrine disruptors such as phthalates can affect male reproductive function and “lead to lifelong reproductive harm.”
Swan says a limitation present in many recent studies of microplastics is that samples may be inadvertently exposed to microplastics present in the environment, leading to distorted impressions of what was actually present in the person.
She notes that similar quality control issues arose nearly a quarter-century ago, when scientists began measuring phthalates in human tissues.
“I think there has to be a lot of caveat to say that this is really just the beginning,” she says. “It’s suggestive, it’s important and it’s preliminary.”
Researchers at the University of New Mexico developed a quality control process to protect samples as much as possible from accidental exposure to microplastics. Campen says there is so much plastic in the human body that the amount that could contaminate samples is “insignificant.”
More broadly, however, he acknowledges that the field faces enormous challenges in the future – particularly when it comes to establishing a stronger link between these tiny particles and a decline in health or disease. reproductive.
“A lot of the problem is that they’re ubiquitous. There are no proper controls anymore. Right? Everyone is exposed,” he says.
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