A new small-scale study builds on evidence that male fertility is at risk from environmental toxics.
A new pilot study shows that microplastics — plastic particles that are smaller than five millimeters or close to the size of a short rice grain – can be found in human testis and semen, according to the paper published last month in Science of The Total Environment.
While experts believe more data are needed
to confirm the findings, this study sheds light on the possible penetration of
microplastics into the human reproductive system and the urgency for
understanding their potential health impact.
Led by researchers from Peking University
in China, the small-scale study analyzed six testis and 30 semen samples for
the presence of microplastics using two different laboratory techniques.
Microplastics were detected in both human testis and semen, with the abundance
in the testis significantly higher than that in semen.
The researchers found differences in the types of microplastics predominating in either testis or semen.
While
polystyrene, a main ingredient for plastic foams, was the most abundant polymer
in the testis samples; polyethylene, which is commonly used for packaging, and
polyvinyl chloride, which makes PVC pipes, were predominant in the semen.
Additionally, they concluded that microplastics ranging from 20 micrometers to
100 micrometers, which is the average diameter of human hair, were the most
common in testis, while those in semen had bigger sizes.
The fact that tiny plastic particles were found in human testis and semen is "no surprise", Dick Vethaak, an ecotoxicologist and emeritus professor at Vrije Universiteit in Amsterdam who has been investigating microplastics but is not involved with this study, told Environmental Health News (EHN).
However, whether it is true
that the larger microplastics can penetrate the male reproductive organs, as
reported in this study, still presents "quite a question mark."
"It's a pilot study that, in my
opinion, provides preliminary evidence that microplastics are present in human
testis," Vethaak said. "But before we can draw any definite
conclusions, I think we need more data."
The paper's lead authors did not respond to
the interview requests by EHN.
How widespread are microplastics?
Typically derived from plastic breakdowns
or used as an ingredient in commercial products, microplastics can be as
ubiquitous as plastic products are. As microplastics transverse through the
global environment — from the French Pyrenees to
Arctic sea ice — these particles also permeate our daily lives,
with traces found in drinking
water, food and air.
Previously, Vethaak and his collaborators
have identified microplastics in human blood.
"If it's in the blood, it can in fact go everywhere in your body," he
said, adding that mounting scientific evidence has also indicated that
microplastics can enter the human gut, lungs and placenta. Despite their
omnipresence, the health impact of microplastics still remains unclear due to
scant scientific evidence.
"An important first step"
"I do think it's an important first
step," Douglas Walker, an environmental health professor at Emory
University who is not involved in this study, told EHN about
the new paper. "I think [the researchers] are establishing a foundation to
show that they're being detected in different types of tissues."
Walker, whose lab has been trying to develop a scalable and reliable exposure assessment method for microplastics, said the authors in this study "did take acceptable steps" to ensure the microplastics measured in the analysis were actually present in the samples versus contaminations introduced during the experiment.
"One of the challenges that we face in
developing methods to measure microplastics — and one of the reasons that they
are so difficult to quantify — is that microplastics are everywhere,"
Walker said. "If you go into a research laboratory, one of the first
things you'll notice is that just about everything is plastic there."
Still, echoing Vethaak's point, Walker said
the study's results on the larger microplastics can be "a little
concerning," especially given that previous evidence has typically linked
smaller particles to the human body uptake.
In addition, given the small sample size of
this study, Walker warned against drawing conclusions on the potential health
impact. "It shows the potential for microplastics to exert some effects on
the male reproductive organs," he said. "What that effect is, we
can't say at this point."
Microplastics' unknown health impact
Shanna Swan, who is a leading reproductive
epidemiologist from Icahn School of Medicine at Mount Sinai and is not involved
in the study, told EHN that, at this point, scientists
"can only speculate" the impact of microplastics on human health
based on the chemicals that have been studied in plastics — such as phthalates
and polychlorinated biphenyls (PCBs). Swan is also an adjunct scientist with Environmental
Health Sciences, the publisher of EHN.
"We know a lot about what those
[chemicals] do individually, but what they do in the form of a microplastic or
nanoplastic, we don't know yet," said Swan, whose research helped underpin
that global human sperm count and quality are declining at an alarming rate.
In addition, emerging studies in animal models, such
as mice, also pointed to microplastic exposures to the potential adverse
outcomes in spermatogenesis and sperm quality, hinting at the possible risk of
these particles for male fertility health in mammalian organisms.
"We know testosterone levels are
decreasing worldwide," she said. "Is that related to the presence of
microplastics in their organs? I don't know — that is an open question."
Huanjia Zhang is a science journalist based
in Baltimore. Follow him on Twitter at @huanjia_zhang.
