Chewing gum can shed microplastics into saliva, research finds

A new study quantifies the amount of microplastics in chewing gum. (Delmaine Donson/E+/Getty Images via CNN Newsource)

Are you keeping a mental list of all the sources of microplastics finding their way into your daily life? You may have another culprit to consider: It’s gum, according to a new pilot study that found chewing just one piece can release hundreds to thousands of microplastics into saliva.

The study is currently being peer-reviewed and will be presented at the biannual meeting of the American Chemical Society in San Diego Tuesday. Once the review is complete, the authors hope the report will be published in the Journal of Hazardous Materials Letters later this year.

“Our goal is not to alarm anybody,” said senior study author Dr. Sanjay Mohanty, associate professor at the Samueli School of Engineering at the University of California, Los Angeles. “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.”

Microplastics are fragments of polymers that range in size from less than 0.2 inch (5 millimetres) to 1/25,000th of an inch (one micrometre). Plastics smaller than that are considered nanoplastics, which are measured in billionths of a meter.

Polymers are chemical compounds with long chains of large and repetitive molecular units called monomers, which are known for durability and flexibility. Most plastics are synthetic polymers, whereas natural polymers include cellulose from plants. Chewing gum typically contains synthetic or natural polymers for better texture, elasticity and flavor retention, the authors said.

Microplastics enter the body via ingestion and inhalation, according to previous research, and scientists have discovered their presence in various body parts or fluids including the blood, lungs, placenta, brain and testicles. That’s why the authors said they wanted to identify other possible sources of microplastic ingestion and their concentrations.

“Chewing gum is one of the foods we chose because it is the only food where plastic polymer is used as an ingredient,” Mohanty told CNN via email. “Other foods are contaminated with microplastics because of how they are processed and packaged.”

To the authors’ knowledge, their study is the first “that examined or compared microplastics in chewing gums available commercially,” Mohanty added.

Isolating microplastics from gum

The team’s findings are based on 10 gums popular in the United States. Half of the samples were synthetic, and the other half were made with natural ingredients.

Most, if not all, gum product labels and websites do not disclose what their gum base includes nor how they are processed. This lack of transparency also leaves researchers “no way to know where and how microplastics came into the gums we tested,” Mohanty said — and no way for consumers to know the full composition of the gums they are buying.

One human participant would chew a gum for four minutes; during that time frame, every 30 seconds a researcher collected the secreted saliva in a centrifuge tube.

The participant then rinsed their mouth three to five times with highly purified water, and the researchers mixed the rinse sample with the saliva sample to ensure all microplastics in the mouth were captured. This entire process was repeated seven times for each gum.

Some gums were chewed for 20 minutes total with saliva collected every two minutes, so the team could determine how the number of microplastics shed depended on the chewing time.

To identify the types and amounts of microplastics in gum, the authors used various methods of filtration and chemical analysis such as microscopy. The research team also subtracted microplastics found in an initial rinse sample from those in the chewing gum saliva samples to accurately estimate the number of microplastics released from chewing gum.

Analysis revealed that just one gram of chewing gum released approximately 100 microplastics on average, with one gram of some gums releasing as many as 637 microplastics. A typical stick of gum can weigh anywhere from one gram to several grams, according to various reports.

Additionally, 94 per cent of microplastics were released within the first eight minutes of chewing.

The authors were surprised to find that chewing natural gums didn’t really make a difference. The average number of microplastics in one gram of synthetic gum was 104, and in natural gum it was 96.

Both types also predominantly released four types of synthetic polymers: polyolefins, polyterephthalates (or polyethylene terephthalate), polyacrylamides and polystyrenes. These are some of the same plastics used in everyday plastic consumer products, Dr. Tasha Stoiber, senior scientist at the Environmental Working Group, a nonprofit environmental health organization, said via email. Stoiber wasn’t involved in the research.

“That microplastics were released is not unexpected,” said Dr. David Jones, a teaching fellow in the School of the Environment and Life Sciences at the University of Portsmouth in England, via email. Jones wasn’t involved in the study.

“If we subject any type of plastic to stress, be it heat, friction, sunlight, seawater, or in this case vigorous mastication, we know that microplastics will be released from the plastic material,” Jones, also founder and CEO of the marine conservation charity Just One Ocean, added. “We inhale, ingest and drink something like 250,000 plastic particles a year without trying. … But at least we now have some robust data and it is a good starting point for further research.”

“Gum is safe to enjoy as it has been for more than 100 years,” the National Confectioners Association said via email. The trade group has member companies that make and sell gum. “Food safety is the number one priority for U.S. confectionery companies, and our member companies use only FDA-permitted ingredients.”

What’s unknown about gum microplastics

The average size of gum microplastics was 82.6 micrometers — think the thickness of paper, or the diameter of some human hairs. The chemical analysis tools used in the study can’t identify particles smaller than 20 micrometers, Mohanty said.

This constraint means the findings missed any smaller microplastics and nanoplastics and therefore may be underestimates, said Dr. Leonardo Trasande, director of the New York University Center for the Investigation of Environmental Hazards, via email. Trasande wasn’t involved in the study.

Why synthetic polymers were found in the natural gums, too, is also questionable, experts said. But polyolefins are commonly used in the food industry for packaging, so this could be a reason why, the authors said.

The unexpected finding may also occur if manufacturers use polymers when they shouldn’t, if there was a lab contaminant or if there was a measurement error, Dr. Oliver Jones, a professor of chemistry at RMIT University in Australia, said in a statement released by the Science Media Centre. Jones wasn’t involved in the study.

“As producers rarely report the composition of gums, it is difficult to ascertain the source of microplastics found in natural chewing gums,” they added.

Also, some of the polymers — such as polyterephthalates, often found in water bottles — identified in the synthetic gums aren’t known to be present in synthetic gums in general, Dr. David Jones of the University of Portsmouth said.

Some regulatory agencies have taken the stance that there is no need to be concerned about microplastics in food and water since there isn’t evidence that they cause harm, he said.

“This is totally the wrong approach. We should be taking the precautionary approach and assume that they do,” he added. “We need to be investing in research to understand how this will impact on our health now so that we can start to mitigate the consequences.”

Even if any potential effects on the human body are unknown, the study does put into perspective the other ways chewing gum can contribute to environmental pollution when inappropriately discarded, experts said.