Chewing gum can shed potentially harmful microplastics into saliva, warns new research. A pilot study found that the popular product can release hundreds to thousands of microplastics per piece into saliva and potentially be ingested.
Previous research has shown that people are exposed to the tiny fragments - linked to cancer and heart disease - through everyday items including chopping boards, clothes and cleaning sponges. Principal investigator Sanjay Mohanty, an engineering Professor at the University of California, Los Angeles (UCLA), said: “Our goal is not to alarm anybody.Scientists don’t know if microplastics are unsafe to us or not.
"There are no human trials. But we know we are exposed to plastics in everyday life, and that’s what we wanted to examine here.”
Scientists estimate that humans consume tens of thousands of microplastics every year through food, drinks, plastic packaging, coatings, and production or manufacturing processes. But, until now, chewing gum hadn't been studied as a potential source of microplastics.
Prof Mohanty and a graduate student in his lab, Lisa Lowe, wanted to identify how many microplastics a person could potentially ingest from chewing natural and synthetic gums. They explained that chewing gums are made from a rubbery base, sweetener, flavourings and other ingredients.
Natural gum products use a plant-based polymer, such as chicle or other tree sap, to achieve the right chewiness, while other products use synthetic rubber bases from petroleum-based polymers. Ms Lowe said: “Our initial hypothesis was that the synthetic gums would have a lot more microplastics because the base is a type of plastic."
The team tested five brands of commercially available synthetic gum and five brands of natural gum. Prof Mohanty said they wanted to reduce the human factor of varied chewing patterns and saliva, so they had seven pieces from each brand all chewed by one person.
In the lab, the person chewed the piece of gum for four minutes, producing samples of saliva every 30 seconds, then a final mouth rinse with clean water, all of which got combined into a single sample. In another experiment, saliva samples were collected periodically over 20 minutes to look at the release rate of microplastics from each piece of gum.
The research team then measured the number of microplastics present in each saliva sample. Plastic particles were either stained red and counted under a microscope or analysed by Fourier-transform infrared spectroscopy, which also provided the polymer composition.
Ms Lowe measured an average of 100 microplastics released per gram of gum, though some individual gum pieces released as many as 600 microplastics per gram. A typical piece of gum weighs between two and six grams, meaning a large piece of gum could release up to 3,000 plastic particles.
If the average person chews 160 to 180 small sticks of gum per year, the researchers estimated that could result in the ingestion of around 30,000 microplastics. If the average person consumes tens of thousands of microplastics per year, gum chewing could greatly increase the ingested amount.
Ms Lowe said: “Surprisingly, both synthetic and natural gums had similar amounts of microplastics released when we chewed them."
She added that they also contained the same polymers: polyolefins, polyethylene terephthalates, polyacrylamides and polystyrene. The most common polymers for both types of gum were polyolefins, a group of plastics that includes polyethylene and polypropylene.
Most of the microplastics detached from gum within the first two minutes of chewing. But Prof Mohanty says they weren’t released because of enzymes in saliva breaking them down.Instead, the act of chewing is abrasive enough to make pieces flake off.
And after eight minutes of chewing, 94% of the plastic particles collected during the tests had been released. Ms Lowe suggests that if people want to reduce their potential exposure to microplastics from gum, they chew one piece longer instead of popping in a new one.
The study was limited to identifying microplastics 20-micrometers-wide or larger because of the instruments and techniques used. Prof Mohanty says it’s likely that smaller plastic particles were not detected in saliva and that further research is needed to assess the potential release of nano-sized plastics from chewing gum.
He added: “The plastic released into saliva is a small fraction of the plastic that’s in the gum. So, be mindful about the environment and don’t just throw it outside or stick it to a gum wall.”
The team are due to present their findings at the spring meeting of the American Chemical Society (ACS) in San Diego, California.