In a startling discovery, researchers in China found microplastics in every human semen sample tested, raising urgent questions about the potential impact of plastic pollution on male fertility and human health.

Widespread Contamination and Declining Sperm Counts

Over recent years, researchers have uncovered a disturbing trend: men’s sperm counts have been steadily dropping. The rate has been about 1.6% yearly since 1963. In 2018, men’s sperm counts were half those recorded only five decades earlier. The trend is accelerating — sperm counts have been dropping at a rate of 2.6% yearly since 2000.

These developments are shocking. Professor Hagai Levine from the Hebrew University of Jerusalem’s Hadassah Braun School of Public Health, one of the researchers who published these results in 2018, did not mince words. He calls these findings a “canary in a coal mine” and, if not mitigated, “could threaten mankind’s survival”.

Levine argues that declining sperm counts may be pegged to epigenetic changes, that is changes in the way our genes work due to environmental or lifestyle factors.

Some of these factors that contribute to declining sperm, and hence poor fertility, include bad diet, sedentary lifestyles, stress, and alcohol and drug use.

However, environmental factors — things we’re all unwilling exposed to — seem to be the more likely culprit. A 2023 meta-analysis that reviewed the results of 25 studies found that men who had been exposed to certain classes of pesticides had significantly lower sperm concentrations. Studies have also linked damage to fertility with chemicals found in household medications, in the air, and in plastics.

In this context, the new findings may add another piece to the male infertility puzzle. Researchers at the Qingdao University in China detected microplastic in every semen sample from 40 healthy men. Although they didn’t reach the same 100% rate, previous studies in Italy and China found microplastics in 60% and 50% of sperm samples, respectively.

Microplastics are tiny plastic particles, often less than five millimeters in size, that result from the breakdown of larger plastic waste. They’re literally everywhere. They’ve been found inside human organs, feces, breast milk, placentas, blood, and — as these studies show — sperm. It’s not clear how these tiny and invisible plastic fragments are affecting human health, although studies in the lab show that they can affect human cells in a petri dish.

A Rising Reproductive Concern

Concerning fertility, study author Ning Li of Qingdao University told The Guardian that “[mouse studies] demonstrate a significant decrease in viable sperm count and an uptick in sperm deformities, indicating that microplastic exposure may pose a chronic, cumulative risk to male reproductive health.”

The research identified eight different types of plastics in the samples. Polystyrene, used in packaging, was the most common, followed by polyethylene from plastic bags, and PVC.

If microplastics are indeed impacting the reproductive process, the consequences for human populations could be dire soon. More than 180 nations are negotiating a UN treaty to regulate plastic pollution.

The findings appeared in the journal Science of the Total Environment.