Solving a sticky litter problem

My husband vividly recalls being made to write out ‘the mastication of glutinous substances is obnoxious’ 100 times on the blackboard when caught chewing in class. Although symbolising the anti-social mindlessness of adolescence for many a schoolmaster, the problems associated with chewing gum are, regrettably, not confined to the Just William classrooms of yesteryear.

Naughty girls and boys do not seem to lose the habit of irresponsible gum disposal as they grow older, but their discarded gum does migrate from the undersides of school desks to public pavements where it becomes a serious problem for local authorities. With the Local Government Association (LGA) estimating that gum removal costs councils in England and Wales £60 million annually, chewing gum litter is not just an eyesore but represents an increasingly obnoxious strain on constricted council budgets.

Up a gum tree

There is evidence that chewing gum has been around in some form for as long as 5,000 years, but in modern times it was originally made from chicle, a natural gum harvested by tapping Manilkara trees, and whose name derives from the Aztec for ‘sticky stuff’. However, Aztec cities would not have been covered in unsightly splodges because chicle breaks down after four to six weeks of exposure to the elements.

The story of chicle in the twentieth century makes for interesting reading, involving political and economic relations between North and Central America, but by the 1960s the major chewing gum manufacturers had all switched to cheaper butadiene-based synthetic rubbers: polymeric hydrocarbons with appetising names like styrene-butadiene, isobutylene and isoprene copolymer.

Synthetic butadiene-based gum is not water soluble and retains its malleability indefinitely. It also forms strong bonds with other polymeric hydrocarbons such as asphalt and rubber soled shoes. Together, these properties mean that, unless a piece of gum does hitch a ride on someone’s foot, human traffic will not damage its structure but will only serve to reinforce the bonds between gum and pavement until it’s left clinging there as stubbornly as a sea squirt on a rock. Each piece then has to be individually power washed away, which the LGA tells us costs £1.50 a time.

Chew-sy customers?

If manufacturers have chemically engineered the problem, couldn’t they engineer a solution? One obvious remedy would be to switch back to chicle-based gums; another would be to create a synthetic, biodegradable polymer. The major gum companies have shown no interest in a return to chicle, although both Wrigley and Kraft have patented synthetic, biodegradable alternatives. Whether they have any real appetite for bringing them to market or are simply flapping their gums remains to be seen.

In 2010, Bristol University spin-out company Revolymer released a gum called Rev7, claiming 50% could be removed through conventional street cleaning. If a small research team is capable of creating such a product, why haven’t the major players already done the same? The main barrier seems to be that it is difficult to create a chewing gum that biodegrades but has the properties consumers have come to expect. Similarly, although a number of smaller companies have put natural chicle gums on the market, they don’t seem to be winning over the masticatory masses.

How do these different gums really compare? Is butadiene’s dominance merely a matter of habit? It seemed there was no way to settle this question except through scientific testing, and I am delighted to be able to present the results of Isonomia’s first taste test.

Natural gum to chicle your fancy: a prescient depiction of the Isonomia taste test from Adams, 1919. Public domain, via Wikimedia Commons.

Ideally I would have compared a popular synthetic gum with both the chicle and biodegradable synthetic alternatives, but unfortunately Rev7 doesn’t seem to have fared well commercially and could not be sourced. Thankfully, the chicle counter culture is rather healthier, and I was able to conduct a synthetic-versus-natural blind test with a small group. Participants were asked to rate the two gums from one to five in six areas: immediate intensity of flavour; longevity of flavour; quality of flavour; chewability; mouth feel; and overall masticatory experience. They were also asked to identify which gum was which and describe the main differences between the two.

All were able to identify the two gums, and the synthetic rated higher than the chicle in every area except quality of flavour, for which the scores were equal. While the consensus was that the synthetic gum had longer lasting flavour and was immediately easier to chew, a third of subjects found the chicle gum more pleasant over the long term, as prolonged chewing made the synthetic sample increasingly like, well, a piece of synthetic rubber.

Interestingly, in the averaged results the natural gum was only one point behind the synthetic in almost every category. If chicle’s performance is close to that of the butadiene based gums, shouldn’t it be relatively easy to manufacture a biodegradable synthetic alternative of equal palatability?

In a second phase of the experiment the chewed samples were stuck to a piece of slate, placed outside and weathered for a month. By week three the chicle pieces had hardened to the point where they crumbled on exposure to pressure, while the synthetic pieces still retained their plasticity. This suggests that littered chicle would indeed break up after a few weeks in the urban environment.

Gum as you are: in our test, the chicle gum (A) weathered faster than the synthetic (B). Photo: Steve Watson.

Gum control legislation?

If a change of tack on chicle isn’t in the offing, then perhaps enforcement is the answer. The Clean Neighbourhoods and Environment Act 2005 gave councils new powers by including chewing gum under the definition of ‘litter’, meaning that fixed penalty notices could be issued for dropping gum. In 2013, Milton Keynes Council floated a more radical idea – a city centre chewing gum ban. The proposal received positive feedback on social media and was supported by local businesses; however, like a well-trodden piece of gum, it never got off the ground.

There is a precedent for such a ban. In 1992, Singapore banned the import and sale of gum to prevent the disruption to the public transit system that irresponsible commuters were causing by sticking it on train doors. However, with the UK’s fervour for chewing second only to that of the US, a nationwide ban seems unlikely.

If we can’t change or control gum, perhaps we can make chewers fund the costs of cleaning up, and this is exactly what the LGA called for last November. The Waste Framework Directive allows member states to implement measures under the polluter pays principle to require the producers and distributors of a material to meet the costs of its waste management. However, for the most part the UK prefers a system of council-funded waste collection and street scene services.

The LGA’s statement does seem to have caught the attention of MPs, and this January Wrigley’s Senior Manager for Corporate Affairs, Alex West, gave evidence at a Commons CLG Select Committee enquiry on litter. Unsurprisingly, he argued against the LGA proposal, instead advocating education to eliminate littering behaviour, and trotted out the familiar lines that a levy would:

• pass the clean-up cost on to responsible and irresponsible gum disposers alike, not stopping to consider that the current system is even more unfair, as it means that people who never chew gum also share in the costs; and
• make people more likely to litter their gum because they would feel that they had already paid for the clean-up costs, although he could not cite a study to back this.

It will be interesting to see what the Committee concludes. However, producer responsibility isn’t something the UK Government has previously shown much enthusiasm for sinking their teeth into.

Having the gum-ption

In the absence of a solution from manufacturers or legislators, innovators from the waste sector have taken up the challenge. Gumdrop is a company providing gum recycling bins and collections, and has partnered with universities, shopping centres and Swansea and Herefordshire councils. Their bins are actually made of recycled gum and are easy to spot.

The idea of new, more accommodating bins is an interesting one. Anyone fascinated by constellations on our streets will have noticed that gum concentrations are highest near public bins, suggesting that many people try, but fail, to dispose of gum properly. Maybe open top containers would make it easier to get the sticky stuff off one’s finger and into the bin. Also, while sticks of gum come with their own useful wrappers, the gum pellets which now dominate the market have no such additional packaging to facilitate disposal.

Once you’ve begun to notice gum litter, you realise that it’s practically everywhere. The scale of the problem implies that a combination of solutions is needed. Consumer behaviour is clearly important, but manufacturers and legislators could make it harder for litterers to blight our streets. It will take co-operation between the gum and waste industry, with pressure and support from government, to reach a point where it’s the gum rather than our efforts which becomes unstuck.