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Tiny pieces of plastic are infiltrating the large arteries in the neck that carry blood from the heart to the head, with the highest amounts found in fatty buildup in the arteries of stroke survivors, a small study suggests.

The concentration of so-called micronanoplastics in carotid arteries was 51 times higher in plaque from people who'd had a stroke, mini-stroke or temporary blindness compared to amounts found in the walls of plaque-free carotid arteries. Even people with carotid artery plaque who had not experienced any of those conditions still had 16 times more micronanoplastics in their plaque.

"It's not just that diseased arteries have more plastics," said the study's lead researcher, Dr. Ross Clark, a vascular surgeon and an assistant professor of vascular surgery at the University of New Mexico in Albuquerque. "That is clear. But those with diseased arteries causing symptoms have far more plastics."

The , considered preliminary until full findings are published in a peer-reviewed journal, were presented April 22 at the ·¬ÇÑÊÓƵ's Vascular Discovery Scientific Sessions conference in Baltimore.

Microplastics and nanoplastics mainly result from larger plastic consumer products degrading in the ocean, soil, rivers, lakes or air. Microplastics are less than 5 millimeters in size – about the size of a pencil's eraser – while nanoplastics are microscopic at less than 1,000 nanometers. By comparison, a human hair is about 80,000 to 100,000 nanometers wide.

Micronanoplastics are omnipresent in the environment and enter the human body when people inhale or ingest them. Previous studies have shown that they are present in the lungs, liver, placenta, breast milk, urine and blood.

The new research comes on the heels of a study published in February in the journal revealing the presence of microplastics in brain tissue and a 2024 study in the that found people whose carotid artery plaque contained microplastics had a higher likelihood of having a stroke, heart attack or dying within three years.

"These new findings add another small piece of data to the growing pile of evidence to guide our thinking on what is the current state of microplastics and nanoplastics in human tissue and give the first glimpse as to what they could be associated with," Clark said.

In the study, researchers looked at carotid artery tissue samples from 48 people: 35 deceased tissue donors with no plaque; six people whose arteries were more than 80% filled with plaque and who had surgery to clear it but never had symptoms; and seven people whose carotid arteries were more than 50% filled with plaque who had surgery to remove the buildup and also had symptoms, which the researchers defined as a stroke, mini-stroke or temporary loss of vision caused by clogged neck arteries.

People with plaque but no symptoms had an average 895 micrograms of micronanoplastics for every gram of plaque analyzed, compared to 57 micrograms of micronanoplastics for every gram of healthy carotid artery tissue. People who'd had symptoms had 2,888 micrograms of micronanoplastics per gram of plaque.

Among people with a high concentration of plastics in their plaque, researchers noted differences in gene activity in plaque-stabilizing stem cells and less activity in anti-inflammatory genes of macrophages, a type of white blood cell, compared to people with low plastic levels.

"Not only do we see the plastic concentrations correlate with how dangerous the plaque is for the patient, but these findings may give some insight into why," said Dr. Kimberly Kicielinski, a cerebrovascular neurosurgeon and an associate professor in the department of neurosurgery at the Medical University of South Carolina in Charleston.

"The findings hint that the white blood cells respond differently in the presence of plastics," said Kicielinski, who was not involved in the study. "This suggests that the immune process is out of whack."

Clark said more research is needed before drawing any conclusions about whether the micronanoplastics were destabilizing or accelerating carotid artery plaque formations or affecting the immune system.

"It is far too early to really understand what role these things are playing, if any," he said. "The microplastics might be inert and simply attracted to areas where other biological things are going on."

But the fact that micronanoplastics are so pervasive in what we eat and drink that people cannot prevent them from penetrating human tissue is troubling on its own, Clark said.

"And it's getting worse," he said. "Even if we stopped creating plastics today, these substances continue to break down and bioaccumulate. That in and of itself should give us some concern. But we don't have any idea what they are doing when they get into our bodies. We are just discovering that they are there."