A study by St. Mary’s University researchers found that microplastics can shorten lifespan and disrupt reproduction in microscopic worms, and also act as toxic vehicles, carrying chemicals and plastic additives into the body after ingestion into the organism.
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Jennifer Harr is a biology professor and researcher who specializes in biochemistry, epigenetics and forensic science who has been at St. Mary’s University since 2019. Harr led the study and her team of undergraduate researchers.
Their findings were published in December in Microplastics, an open access, peer-reviewed journal focused on the science behind microplastics, which are tiny fragments of plastic that have become an increasingly important point of research in recent years given their potential impacts on human health.
Scientists already know that these fragments are everywhere in our environment, turning up in the water, soil, atmosphere, marine life and even human tissue. What’s less clear is what kind of health impacts they might be having on us, and whether they can transport toxins from the environment into our bodies.
Microplastics are everywhere
Microplastics are tiny fragments of plastic that break off from larger plastic items. Instead of biodegrading into the environment, most plastics break down into smaller pieces that can persist indefinitely.
Although definitions vary, microplastics can be as large as a grain of salt or as small as bacteria. Nanoplastics are even tinier, and can be even smaller than our cells.
Researchers started looking at the effects of plastic pollution in the ocean in the 1960s, and more focused studies on microplastics came in the mid-2000s. Since then, as researchers have learned more about how ubiquitous microplastics are, the field has quickly expanded.
“People have been interested in microplastics in aquatic environments for a long time,” Harr said. But research into what microplastics may be doing inside animals and humans is newer, accelerating especially in the last few years. “The field is moving fast.”
Humans are exposed to microplastics mainly through drinking water, food, the atmosphere and cosmetics. Although estimates exist, researchers don’t know how much of these tiny fragments we regularly ingest.
Nonetheless, researchers have detected microplastics in many of our organs and tissues, including the brain and blood. They have also been found in urine, breastmilk, semen and meconium — a newborn’s first stool.
In laboratory settings, researchers have tied microplastic exposure in certain animals to inflammation, reproductive issues and hormone disruptions.
But we don’t know whether those impacts transfer to larger organisms like humans. “We don’t have that for humans,” Harr said, “because we can’t experiment on humans.”
The research is also somewhat muddy since labs are often using different microplastic sizes, shapes and varying measurements, making comparisons difficult.
Another problem, researchers have found, is in-lab contamination and its potential to inflate results. A 2026 study found that nitrile and latex gloves can transfer particles that mimic microplastic particles, resulting in false positives and overestimating the presence of microplastics.
An earlier 2024 study found that microplastics were everywhere in the lab, and that contamination was likely in studies without strict handling procedures. That means that exposure levels used in lab experiments may not perfectly mirror what humans and other organisms encounter day to day.
It has also been unclear whether the plastic fragments might be harmful on their own, or if they could also be carrying harmful substances from the environment into organisms that they otherwise wouldn’t have been exposed to.
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In 2024, Harr and her lab — using transparent microscopic worms — set out to get a clearer picture of this potential mechanism.
Microplastics act as vehicles for toxins
Harr’s lab at St. Mary’s University focuses on epigenetics, the study of how the environment can affect gene expression without altering DNA. The field has implications for toxicology and forensic science.
In 2024, Harr and her lab were awarded a $670,000 four-year grant from the National Institutes of Health to research how microplastics might carry toxins, like environmental toxins and plastic additives, into organisms.
Harr’s lab is undergraduate-driven. Harr said she was convinced by an undergraduate environmental studies student in her lab during the grant writing process to focus on microplastics, an area of research she had not yet been involved in.
Harr and her research team chose C. elegans, microscopic roundworms that live in the soil, as their model organism. The worms have been favored by researchers for their translucence — making it easier to track what’s happening inside the organisms – and because they have similar genetic pathways to humans.
The team exposed the worms to microplastics, both with and without additives and chemicals to see what impacts they might have on the organism’s biology.
They found that the tiny plastics alone caused harm after ingestion, decreasing lifespan at high enough exposures and disrupting reproduction. They also found that the health impacts were generally more severe if the plastics were combined with dibutyl phthalate (DBP), a plastic additive that helps with flexibility.
DBP’s use in plastics has been restricted in many consumer products, but it served as a proof-of-concept that plastic additives could be carried from the environment into organisms, Harr explained. “Even if you eliminate it from the plastic, they can be in the environment as contaminants.”
Other researchers have found that organisms digest and clear microplastics without significant accumulation, such as in this 2026 study on earthworms. Harr noted that size may be crucial: larger fragments may remain in the digestive tract and be expelled, while much smaller particles could be more likely to cross into tissue, potentially carrying toxins with them.
“Overall, our results show that chronic [microplastics] exposure has detrimental effects on reproduction and reduces lifespan [of the worms],” the paper concludes. “We demonstrate that co-exposure of [microplastics] and DBP exacerbates the defects observed. [Microplastics] mediate DBP delivery in C. elegans, further decreasing fertility and lifespan and triggering a stress response.”
What comes next
Harr said she and her lab are working on a follow-up study, which will look at differences in the biological impacts depending on how weathered or roughened up the microplastics are compared to more pristine microplastic beads, Harr said, in an effort to more closely mimic what organisms are exposed to in the environment versus lab settings.
She is also working on securing funding to look more closely at the mechanism behind reproductive damage from microplastics and DBP.
“We see that there’s an effect,” Harr said. “But the question is, why? What is happening on the molecular level, on the cellular level, and as I mentioned … what’s happening at the DNA level?”
The U.S. Department of Health and Human Services’ Advanced Research Projects Agency for Health (ARPA-H) is aiming to accelerate microplastics research through its STOMP program.
“In the animal models, I would argue it does have an effect,” Harr said. “In humans, we just don’t have that answer yet.”
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