Microscopic Menace — Scientists Discover Plastic Nanoparticles in Men’s Testicles

The average person eats about 5 grams of plastic per week — about the amount found in one credit card.¹ So it’s no wonder that tiny pieces of plastic are turning up throughout the human body, including in places you might not expect. Following research that found plastic particles in the human bloodstream,² and another study that found them in the human heart,³ scientists have now discovered microplastics in men’s testicles.⁴

The study’s lead author, Dr. John Yu, a toxicologist in the College of Nursing at the University of New Mexico, wasn’t expecting microplastics to have infiltrated the testicles, given the tight blood-tissue barrier in the male reproductive system, known as the blood-testis barrier.

As noted in Pharmacological Reviews, “The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body.”⁵ The presence of microplastics in the testes suggests that microplastics can bypass or penetrate the BTB, raising concerns about their ability to infiltrate other protected and sensitive tissues in the body, as well as their potential impact on reproductive health.

Microplastics Found in Human and Dog Testicles

For the study, researchers from the University of New Mexico measured 12 types of microplastics in 47 canine and 23 human testes.⁶ Microplastics are small plastic particles that are less than 5 millimeters in size. They may be intentionally manufactured for use in products like cosmetics, personal care items (such as exfoliating beads in face scrubs) and industrial applications. They also include microfibers shed from synthetic clothing during washing.

Microplastics also include small plastic fragments that result from the breakdown of larger plastic items, such as bottles, bags and other plastic debris. This breakdown can occur due to environmental exposure, such as sunlight (photodegradation), ocean waves and weathering.

The study involved both human and dog testicles, as dogs share many physiological and anatomical similarities with humans, making them a valuable model for studying human diseases and conditions.

Further, because dogs share the same living environment as humans, they are exposed to similar pollutants, chemicals and other potential hazards. As such, they’re often considered sentinel animals,⁷ meaning they can serve as early warning indicators of potential health risks and environmental hazards that might also affect humans.

The study found microplastics in all the canine and human testes examined, with significant differences between individuals. On average, total microplastic levels were 122.63 µg (micrograms) per gram (g) in dogs and 328.44 µg/g in humans.⁸ Both humans and canines had similar proportions of the main types of microplastics, with polyethylene (PE) being the most common.

Polyvinyl chloride (PVC) was also detected and linked with lower sperm count in dog testicles. Higher levels of PVC were also associated with decreased weight of the testicles, as was polyethylene terephthalate (PET).⁹ A 2023 study similarly found microplastics in the male reproductive system, including the testis and semen.¹⁰

Are Microplastics Involved in Male Infertility?

It’s estimated that 11 million tons of plastic waste enter the world’s oceans annually — an amount that could nearly triple by 2040.¹¹ What’s the end result of a plastic world? An impending fertility crisis is upon us. Men experienced a 50% to 60% decline in sperm counts from 1973 to 2011, according to a 2017 study published in Human Reproduction Update.¹²

An update to the study, which includes data from 53 countries and an additional seven years¹³ — 2011 to 2018 — found sperm concentration declined “appreciably” by 51.6% from 1973 to 2018. The percent decline per year doubled, increasing from 1.16% after 1972 to 2.64% after 2000.¹⁴

Total sperm count also declined at an alarming level — 62.3% from 1973 to 2018. A class of plastic chemicals called phthalates, which are so ubiquitous that the U.S. Centers for Disease Control and Prevention has stated “phthalate exposure is widespread in the U.S. population,”¹⁵ may be particularly to blame.

An estimated 8.4 million metric tons of plasticizers, including phthalates, are used worldwide each year,¹⁶ with phthalate production amounting to about 4.9 million metric tons annually.¹⁷ Microplastics often contain phthalates, which can leach out of the material¹⁸ causing endocrine-disrupting effects.