# Why is chewing gum so hard to get off pavements?

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## Summary

Gum bonds to pavements and shoe soles because they are made of similar polymers. Removing it needs steam and scrapers, and costs cities a fortune.

## Description

Those dark round spots all over the pavement are not stains or paint. They are chewing gum, dropped, trodden flat and slowly blackened by dirt. They are also remarkably hard to get rid of.
Why gum sticks so well
The chewy part of gum, the gum base, is made of polymers. They repel water, which is why gum survives being chewed and is not washed away by rain. But they are attracted to oily surfaces, and they form strong bonds with them. Tarmac and the rubber soles of shoes are also made of polymeric hydrocarbons, so gum bonds to them particularly well. It bonds strongly to concrete paving too.
Once gum has been walked in and left to dry, it becomes part of the pavement. And because its long polymers stretch rather than break, you cannot simply flick it off.
Why it costs so much to remove
Getting gum off pavements usually means steam jets and scrapers, working one blob at a time. It is slow, labour intensive and expensive. In Rome, about 15,000 pieces of chewed gum are dropped every day, and removing each one costs the city about one euro.
How much gum is out there?
A lot. In 2000, a study of Oxford Street, one of London's busiest shopping streets, counted about a quarter of a million black and white blobs of gum stuck to its pavement. In 2018 the BBC reported that chewing gum was the second most common form of litter, after cigarette ends.
The city with no gum
Singapore is the exception. It banned the sale of chewing gum in 1992, largely because gum was being stuck on the door sensors of its new underground trains, and its pavements are said to be almost uniquely free of gum. See why chewing gum is banned in Singapore.
Turning gum into something useful
In Britain, a designer called Anna Bullus came up with a way of recycling chewing gum into plastic. Collected gum goes to a recycling plant in Worcester and is turned into material that can be moulded into new things, including shoe soles, cups and the bins used to collect more gum, which her company calls Gumdrops.
What you can do
Wrap your gum in paper or a tissue and put it in a bin. Never drop it. And if it ends up on your clothes rather than the pavement, see how to get chewing gum out of clothes.

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