We are riddled with microplastics. It is in our bloodstream, in our lungs, in our liver - pretty much anywhere you look in the human body, you will find minuscule bits of plastic.
Authors
- Michael Richardson
Professor of Animal Development, Leiden University
- Meiru Wang
Postdoctoral Researcher at Leiden University, Associate Scientist II at Stowers Institute, Developmental Biology, Molecular Biology and Nanotoxicology, Leiden University
And there are many ways for us to ingest, inhale or otherwise absorb these tiny fragments. For example, a single plastic teabag sheds over 10 billion microplastic particles into a cup of tea.
And if you redecorate your home and sand down the old paintwork, the plastic binders in the paint can release microplastics into the air , which you might then inhale. You could swallow them when you drink from single-use plastic water bottles . Now another source of microplastics in the body has been discovered: chewing gum.
Chewing gum contains long molecules called polymers. Some brands of gum contain natural polymers from tree sap. Others contain synthetic polymers derived from the petroleum industry. These various polymers are similar to plastics - and some actually are plastics. Chewing gum polymers, both natural and synthetic, can release microparticles when they are worn down by chewing.
In the chewing gum study - which was presented at the American Chemical Society meeting 25 March - a single volunteer chewed ten brands of chewing gum - five natural and five synthetic. Saliva samples were taken from the volunteer's mouth and put under the microscope. Surprisingly, microplastics were found in both the natural and synthetic chewing gums.
The researchers, from the University of California, Los Angeles, calculated that one piece of gum could shed hundreds or a few thousand microplastic particles into the mouth, where they probably ended up being swallowed.
The types of plastics found in the gums were polystyrenes (used for things like takeaway food containers), polyethylenes (such as those used to make plastic grocery bags) and polypropylenes (which are used to make, among other things, car bumpers and medicine bottles).
But, before we start worrying about the microplastics liberated by chewing gum, we need to know how large they were.
Size matters
The microplastics found in the saliva of the gum-chewing volunteer were 20 micrometres or more in size. That is about the diameter of the thinnest human hair. But from the perspective of a cell in the human body, 20 microns is huge (a red blood cell, for instance, is about seven microns in diameter).
This is important because the microplastics that are known to be capable of harming cells and embryos are 500 to 1,000 times smaller than that (20 to 500 nanometers). These super-small microplastics are called nanoplastics.
Nanoplastics are bad news because they are small enough to be engulfed by living cells via a process called endocytosis. When nanoplastics are absorbed into cells, they can cause all sorts of trouble, such as triggering the cell to produce toxic molecules called reactive oxygen species. These toxins may not kill the cell outright, but they can weaken it.
Likewise, the plastic particles that have been shown to cause birth defects in animal embryos are also the very small ones (the nanoplastics), not the much larger microplastics that were found in the saliva of the gum chewer.
The chewing gum study is fascinating. It shows how easily we can unwittingly expose ourselves to hundreds of microplastics. However, we cannot confidently assign any kind of health risk to chewing gum.
The microplastics that are liberated by the chewing of gum are relatively huge, and we know nothing about the effects - if any - of such large particles in the human body. And we don't know if chewing gum releases nanoplastics at all. The trouble is that nanoplastics are so tiny that they require specialised apparatus to detect them. For that reason, the researchers in the US who studied chewing gum decided not to look for them.
Some commentators think that the potential health risks of microplastics have been exaggerated , while others criticise the quality of some of the scientific studies on microplastics. We are inclined to agree with these criticisms. Hopefully, it will not be too long before we truly understand whether the microplastic scare will turn out to be justified - or just hype.
Michael Richardson receives funding from The Dutch Government.
Meiru Wang does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
