Microplastics are everywhere in our environment: oceans, soils, the air, the bodies of animals. It’s hardly surprising, then, that the tiny fragments have also been found in humans. But a new study is shining troubling light on the quantity of microplastics Americans are consuming each year—as many as 121,000 particles, per a conservative estimate.

Measuring less than five millimeters in length, microplastics derive from a variety of sources, including large plastics that break down into smaller and smaller pieces. Many studies have looked at microplastics in the marine environment, but much remains unknown about the prevalence of these materials within the human body, as well as their impact on human health.

Hoping to fill in some of these gaps, a research team led by Kieran Cox, a PhD candidate at the University of Victoria and a former Link Fellow at the Smithsonian Institute, looked at 26 papers assessing the amount of microplastics in commonly consumed food items, among them seafood, sugars, salts, honey, alcohol and water. The team also evaluated the potential consumption of microplastics through inhalation using previously reported data on microplastic concentrations in the air and the Environmental Protection Agency’s reported respiration rates. To account for factors like age and sex, the researchers consulted dietary intakes recommended by the U.S. Health Department.

Based on this data, the researchers calculated that our annual consumption of microplastics via food and drink ranges between 39,000 and 52,000 particles, depending on age and sex. Female children consume the least and male adults consume the most, the team reveals in the journal Environmental Science & Technology. When microplastics ingested through inhalation are taken into account, the range jumps from 74,000 to 121,000 particles per year.

Speaking to Anne Gaviola of Vice, Cox said he was surprised to discover the extent to which drinking water from plastic bottles impacted total microplastic consumption. The study authors found that people who drink exclusively from plastic water bottles ingest an additional 90,000 microplastics each year, compared to 4,000 among those who only consume tap water. “This shows that small decisions, over the course of a year, really matter and have an impact,” Cox tells Gaviola.

The new study, according to its authors, was the first to investigate “the cumulative human exposure” to microplastics. But in all likelihood, the research tells only a fraction of the entire story. Collectively, the food and drink that the researchers analyzed represent 15 percent of Americans’ caloric intake. The team could not account for food groups like fruits, vegetables, meat and grains because there simply is not enough data on their microplastic content.

“Our estimates of American consumption of microplastics are likely drastic underestimates overall,” the study authors write.

Just what this means for human health is not clear. According to the study authors, there is evidence to suggest that microplastics can penetrate the human body through “cellular uptake in the lungs or gut.” Once in the gut, microplastic particles may release harmful toxins. They can also enter tissue and the bloodstream.

“We’re at the point where we know microplastics at some dose could be harmful,” study co-author Garth Covernton of the University of Victoria tells Michelle Ghoussoub of CBC News, “but we’re not at the point where we can say whether what the average person is encountering is the equivalent of one cigarette in a lifetime, or [through] chronic exposure, like a pack a day.”

For those worried about microplastic consumption, cutting out bottled water is a good place to start, the study authors say. But to really get to the heart of the problem, we have to stop producing and using so much plastic.

“We need to reassess our reliance on synthetic materials,” Cox says, “and alter how we manage them to change our relationship with plastics.”