Think you’re avoiding microplastics when you drink from a glass bottle rather than a plastic one? New research found that may not be the case.
A new study, published this month in the Journal of Food Composition and Analysis, found that beverages packaged in glass bottles actually contained far more microplastics than those packaged in plastic bottles and cans. The researchers believe caps may be the culprit.
Microplastics—tiny pieces of plastic less than 5 millimeters long—are pervasive throughout our oceans, soil, food, and air. They can enter our bodies in a number of ways and have been linked to health issues such as infertility, hormone disruptions, cardiovascular disease, and cancer.
“This study challenges the common assumption that glass packaging is automatically safer,” said Nicole Sparks, PhD, assistant professor of environmental and occupational health at the UC Irvine Joe C. Wen School of Population and Public Health. “Components like caps can be a major source of microplastic exposure.”
To determine how packaging affects the amount of microplastics in various beverages, French researchers used a special microscope and chemical analysis to examine water, soda, iced tea, lemonade, wine, and beer sold in France.
All of the samples contained microplastics, the data showed. But the concentrations differed based on the packaging for each beverage:
- Cola, iced tea, lemonade, and beer: These drinks contained significantly more microplastics when packaged in glass bottles—in some cases, the amount of microplastics was nearly 50 times more than in plastic bottles and cans.
- Water: Glass bottles of water had slightly higher microplastic content, but water was the least-contaminated beverage across the board.
- Wine: Quarter-liter “brick” carton packaging was associated with more microplastics in wine, though the level of microplastic contamination for all of the wines tested was relatively low.
Essentially, the amount of microplastics a person is exposed to may differ widely based on what they’re drinking and from which container. An average plastic bottle of water may contain about 1.6 microplastics per liter (MPs/L), for example, while a glass bottle of lemonade may contain over 100 MPs/L.
It’s worth noting that the researchers only tested for microplastics, not nanoplastics. These much tinier particles “may have gone undetected, reinforcing the need for further investigation,” added Rene Caballero, PhD, research toxicologist at NSF, a public health and safety organization based in Michigan.
If you find it strange that glass-bottled beverages were more contaminated than plastic ones, you’re not alone. “We were expecting the opposite result,” study author Iseline Chaïb, a PhD student with the French Agency for Food, Environmental and Occupational Health & Safety, said in a press release.
But there’s a theory as to why: the cap.
Manufacturers often use paints to cover metal caps on glass bottles—and those chemicals may leach microplastics into the beverages, researchers said.
In their testing, the team noted that the microplastics found in glass-bottled drinks usually had the same color, shape, and polymer composition as the paint used on the caps. Plus, researchers found tiny scratches on many of the caps.
“These caps shed polyester-based particles during manufacturing, storage, or sealing, likely due to friction and abrasion,” Sparks told Health.
Once researchers cleaned the caps, the amount of microplastics significantly dropped. Microplastic contamination fell from 287 MPs/L to 106 MPs/L when researchers blew air onto the caps, and further dropped to 87 MPs/L when the caps were also rinsed with a water and alcohol mixture.
Another piece of evidence? Even though wines are usually packaged in glass bottles, the use of a cork instead of a cap likely explains why the amount of microplastic contamination was so much lower.
Cleaning caps or getting rid of them doesn’t completely solve the issue—airborne particles, contaminated water and ingredients, and plastic factory equipment can also add microplastics into beverages, Caballero told Health.
However, researchers and experts agree the findings should encourage beverage manufacturers to change their processes to protect consumers.
“The elevated levels detected in beverages from glass bottles are concerning, as they suggest that glass with painted caps isn’t a safe alternative to plastic, prompting a reevaluation of packaging choices,” Amelia Meyer, MSc, a research program manager studying environmentally mediated infectious diseases at Stanford Medicine, told Health.
Microplastics have been detected throughout the human body—in blood, breast milk, the digestive tract, lung tissue, and more. Oral ingestion is thought to be the main way that these particles get into our bodies, said Caballero.
Growing evidence suggests microplastics may be linked to inflammation, oxidative stress, and gut microbiome issues. “These particles may interfere with critical biological systems, including metabolism, reproduction, and development,” said Sparks.
Over time, the microplastics—and the damage they cause—can accumulate and potentially contribute to the development of chronic disease and other health issues, though their effect seems to depend on particle size, shape, chemical composition, and other factors, Sparks explained.
“More research is needed to understand how these findings translate to chronic human exposure,” she said.
People, on average, are exposed to between 39,000 and 52,000 microplastic particles per year—and that’s just through food, estimates suggest.
When it comes to beverages, glass bottles may not be the safe alternative people assume they are. And even though this new study suggested plastic bottled water may be safer, U.S. research from 2024 found that bottled water contains an average of about 240,000 plastic pieces, the majority of which are nanoplastics. Researchers have even found microplastics in tap water, albeit at lower concentrations.
So is it even possible to avoid microplastics when they are so ubiquitous? Probably not, experts agreed. “No container is risk-free,” said Sparks.
But there are various steps that can help you reduce your exposure.
At home, keep your drinks in glassware, stainless steel, or bamboo cups. When you do use plastic containers, avoid putting them in the dishwasher and microwave, Caballero advised, so they don’t leach microplastics into your food or beverages.
When you’re out and about or drinking a store-bought beverage, you don’t need to completely avoid glass bottles—instead, consider rotating between types of packaging, Sparks said.
When in doubt, opt for fresh, unprocessed drinks and snacks—the goal, according to Meyer, is to reduce our overall reliance on packaged beverages in general.