Maybe you saw them. In the summer of 2024—the year before last—volunteers collected signatures on sidewalks and in parking lots across Bozeman. It was hot (except when it wasn’t), windy (except when it wasn’t), and very sunny.

The goal was modest: to place a measure on the city ballot limiting the free distribution of single-use plastic bags at downtown businesses. But the determination was strong, fueled by a growing understanding that plastic isn’t just a waste problem—it’s a human health issue.

We’ve seen the headlines: microplastics have been found in breast milk, lungs, intestines, and nearly everywhere else scientists have looked. In March 2024, researchers reported plastic in carotid plaque, associated with a 450% increase in heart attack, stroke, and death over the subsequent three years. That summer, studies in New Mexico and Brazil identified micro- and nano-plastics in different parts of human brains, likely arriving there via general blood circulation or the olfactory nerve.

Whether residents read the science or the headlines, the campaign gathered 10,482 signatures—impressive in a town of 62,963 voters. In November, a 63% majority voted it into law—a landslide. Bozeman became the first city in Montana to pass a plastic bag ban, and the first in the nation to do so via citizen initiative.
But can plastics really threaten health?

The answer is sprawling. Plastic bags litter landscapes, clog sewers, and harm wildlife. In Montana, they can be eaten by grazing animals, causing fatal intestinal blockages. These are the visible harms of macro-plastics. But as plastics fragment, their risks become more widespread, and less visible.

Plastics don’t break down; they break up into microplastics and even smaller nano-plastics—some comparable in size to smoke particles, viruses, or proteins. These particles travel widely through air, water, and soil, ending up in food and the human body.
What are they doing there? Nothing good.

Early research shows MNPs cause inflammation and cellular damage. Studies suggest they may disrupt brain processes, including the protein-folding linked to dementia. Even if plastic were inert, the rate of accumulation would be concerning. A New Mexico study found a 50% increase in brain plastic levels from 2016 to 2024.

But plastic isn’t inert. It continuously leaches chemicals. Made from fossil fuels and additives, plastics can contain over 16,000 chemicals that migrate out based on heat, acidity, and other conditions. When particles lodge in tissue, they act like tiny Trojan horses, releasing chemicals inside the body.

Many of these chemicals are hazardous—carcinogens, neurotoxicants, and endocrine disruptors that interfere with hormone signaling. These disruptions are linked to obesity, diabetes, reproductive harms, neurodevelopmental conditions, and more.
Exposure is universal. From food packaging to synthetic clothing, from tires to cutting boards, we encounter microplastics daily. Smaller particles are especially concerning, as they can cross into the bloodstream and travel throughout the body.

Where is the hope?

While we cannot remove microplastics from the body, our organs may help clear them. The liver, kidneys, and even the brain’s glymphatic system appear to play roles. In animal studies, reduced exposure led to lower brain plastic levels—suggesting partial recovery is possible.

Reducing exposure matters. Use stainless steel bottles and filtered tap water. Choose glass, ceramic, or metal for storage. Avoid heating food in plastic. Opt for wood or metal utensils, and avoid nonstick coatings.

And what of the Bozeman bag ban?

After passing in November 2024, it was challenged by state attorneys, who argued that citizens lack authority to bring such initiatives. The state prevailed initially, but a second question remains: does blocking local action violate Montanans’ constitutional right to a clean and healthy environment? That case is set for trial in December 2026.

That’s a long way off. In the meantime, Americans will use millions of plastic bags. In four visits to the supermarket, an average American family will use 60 plastic bags. But Bozeman residents have already shown what’s possible. Those who gathered 10,000 signatures are likely already bringing reusable bags—and the 63% who supported them may not be far behind.

The more people learn, the more they act. And that may be the most important shift of all.   

Megan J. Wolff, PhD, MPH is the executive director of the Physician and Scientist Network Addressing Plastics and Health (P-SNAP) and an adjunct instructor at Cooper Medical School of Rowan University, where she teaches a class on Plastics, Microplastics, and Human Health.

 

Elizabeth Ryznar, MD, MSc is a physician in Maryland, Associate Chair of Psychiatry at St. George’s University, and a part-time assistant professor at the Johns Hopkins School of Medicine. The views expressed herein are Dr. Ryznar’s and do not reflect the organizations’ position. She is also an advisory board member of the Physician and Scientist Network Addressing Plastics and Health (P-SNAP)