Every time you chew gum, you’re filling your mouth with plastic

When you pop a piece of gum in your mouth, you might be hoping to freshen your breath, relieve some stress, or just get a bit of flavor. But you could also be getting thousands of microplastics released with every piece you chew.

That’s because most chewing gum itself is made of plastic; gum bases often use synthetic polymers like polyvinyl acetate, a plastic used in adhesives; or styrene-butadiene, a type of plastic rubber used in tires and shoe soles.

Plastic is already everywhere: our bottled water, our soil, even our air. Microplastics can leach into our bodies through all those things, as well as through foods kept or heated up in plastic packaging. But with gum, the exposure is more direct. “Here, the food is the plastic,” says Sanjay Mohanty, an engineering professor at UCLA.

Mohanty is lead investigator on the pilot study that looked at how microplastics from gum can get into our saliva. He conducted the study with Lisa Lowe, a PhD student in his lab, who is presenting their findings at the spring meeting of the American Chemical Society this week.

Mohanty has been studying microplastics for years; he’s done research on how wind can blow microplastics from fertilizers through the air, and how children’s playgrounds can contain more microplastics than other areas of urban parks. Lowe, who grew up in Hawaii and has seen the devastating effects of pollution firsthand, came up with the idea to actually quantify the plastic impact of gum. The topic even surprised some of her classmates. “People don’t really know that gum is plastic,” she says. “It’s just not something that we think about because it’s like food, so we wouldn’t expect it.”

The researchers looked at both synthetic and natural gums, picking five brands of each that are the most readily, commercially available. Lowe herself was the tester: she would rinse her mouth (and take that sample, to see the level of microplastics in her saliva from the start), and then chew a piece of gum for four minutes, spitting out saliva samples every 30 seconds, before a final rinse.

On average, they found that every gram of gum would release 100 microplastics, though some pieces released as many as 600. Most pieces of gum are between 2 and 6 grams, so that means a large piece could release as many as 3,000 microplastics. By some estimates, Americans average one to three pieces a day, but looking at a conservative amount, if someone chewed 160 to 180 small sticks of gum a year, the researchers estimated that could lead to them ingesting 30,000 microplastics.

Before starting the study, Lowe anticipated that the natural gums would have fewer microplastics—but really they released similar amounts. It’s not clear where exactly those plastics are coming from, though; Lowe said it could potentially be from the manufacturing process. 

Their study was also limited in terms of exactly which microplastics they could identify in the saliva: They only looked for pieces of plastic bigger than 20 microns, which are visible under a microscope. That means they didn’t look for nanoplastics—particles smaller than 200 nanometers (a human hair, for contrast, is about 80,000 nanometers wide). Previous research has already found that one bottle of water could contain hundreds of thousands of nanoplastics. “There could be many, many more plastics [released by chewing gum] that are too small to be visible in our sensor,” Mohanty says. 

Lowe also tested chewing the pieces for longer, collecting samples of more than 20 minutes, to see how microplastics were released over time. Most of the microplastics were released within the first two minutes of chewing. After 8 minutes, 94% of the plastic particles collected during the tests had been released. If you’re looking to reduce your microplastic exposure but aren’t quite ready to give up gum, Lowe says this indicates that you could try chewing one piece for longer, rather than starting a fresh piece.

There’s not yet a lot of scientific research on how microplastics affect our health, but there are indications that they’re harming our bodies. “We know it’s not something natural,” Mohanty says. The reserchers hope their study helps people become more aware of another form of microplastic exposure. “When you eat chewing gum, you think you are getting the flavor. You are also getting some plastic with it,” he says. And Lowe also hopes this gets people thinking about how they dispose of their chewed-up gum as well. “It is a source of plastic,” she says, “so it should be disposed of properly.”

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