March 25, 2025

expert reaction to study looking at the number of microplastics found in chewing gum

A preprint published at the American Chemical Society Spring Meeting looks at microplastics in chewing gum. 

Professor Ted Henry, Heriot-Watt University, said: 

“The manuscript reports on the presence of microplastics in natural and synthetic chewing gums with an average of ~100 microplastic particles per gram and each particle with average size of 45-80 micrometers.  

“This quantity of microplastic particles will weigh < 30 micrograms, which is somewhat higher than some other sources of microplastics to which humans are exposed to daily by ingestion (e.g., bottled water, and most foods that have been tested).  

“Exposure to microplastics by respiration of indoor air is higher by some reports, and is likely the highest single source of exposure in humans.  

“It is important to recognize that the amount of microplastic particles to which humans are exposed is a tiny fraction of the total amount of similar-sized natural particles to which humans are exposed on a daily basis, and the human body is quite good at preventing these particles from accumulating in the body and having negative effects on health.  

“Regarding the methodology used in the study, it is not clear the extent to which procedural controls have been incorporated in the methods for microplastic extraction and analyses.  Because microplastics are everywhere including within laboratories and even in the reagents used in laboratories, extensive control procedures are necessary to reduce the occurrence of false positives or erroneously high levels of microplastic particles found in samples.  As with all such studies independent verification of results is necessary to validate findings.”

Prof Oliver Jones, Professor of Chemistry, RMIT University, said:

“This is an interesting preprint, but it has not undergone peer review, so its content may change before it is published, and I could not access the supplementary information. 
“The idea that chewing gum might be a source of microplastics is not that new in itself, but this is the first study to attempt to quantify the potential problem.

“An interesting finding from this study is that they found very similar microplastics of microplastics in both the synthetic and the natural gums, even though there weren’t supposed to be plastics in the natural gums at all. In fact, the data from both groups is almost identical. Logically, this means either

1. i) There were actually microplastics in the natural gums when there shouldn’t have been.
2. ii) There was another source of microplastics common to both groups that had nothing to do with the gum (e.g., lab contamination of some form).
   iii) There was some form of measurement error common to both groups.

“A potential issue is that the authors used a dye called Nile Red to stain the microplastics to make them easier to see. This is a common approach, but the method has potential issues in that Nile Red can stain a wide variety of natural and synthetic particles (1), and some biological materials can autofluorescence, which makes them look like dyed plastic when they aren’t (2).

“I can’t see from the pre-print how these factors were controlled for, but Nile Red based microplastic data are inconclusive without adequate controls.
“If we assume the figures are accurate, 637, micrometre-sized pieces of plastic per gram of gum is a very small amount indeed. Since the lining of the intestine is fairly thick and well-regulated, any particles you swallowed would likely pass straight through you with no impact.

“In short, while microplastics are something we should definitely be keeping an eye on, I don’t think you have to stop chewing gum just yet – although you should certainly dispose of it appropriately in a bin when you are finished with it.”  

1 – Stanton, T., Johnson, M., Nathanail, P., Gomes, R.L., Needham, T. and Burson, A. (2019) Exploring the efficacy of Nile Red in microplastic quantification: a costaining approach. Environmental Science & Technology Letters 6, 606-611.

 2 – Catarino, A. I.;  Frutos, A.; Henry, T. B., Use of fluorescent-labelled nanoplastics (NPs) to demonstrate NP absorption is inconclusive without adequate controls. Science of The Total Environment 2019, 670, 915-920.”

‘Ingestion Risk of Microplastics from Chewing Gums’ by Mohanty et al. was presented at the American Chemical Society meeting at 09:00 UK time on Tuesday 25th March.

Declared interests

Prof Oliver Jones “I am a professor of Chemistry at RMIT University in Melbourne, Australia. I have no direct conflicts of interest to declare. I have previously published research on microplastics in the environment. I have also received funds from the Environment Protection Authority Victoria and various Australian Water utilities for research into environmental pollution.”

For all other experts, no reply to our request for DOIs was received.