Street Science: The Gum We Step In

Gum ball machine on 24th Street.

Gum ball machine on 24th Street.

En Español

More than a ton of gum is stuck to the ground in the Mission District. Millions of pieces of chewing gum. Or more.

That’s actual pieces, not the shadowy stains left behind after someone steams them off. And it’s a low estimate. See below for my back-of-the-envelope math.

Used gum is gross; we could do without knowing it was once in someone’s mouth before making its sidewalk debut. However, it may be better to leave it stuck to the ground instead of cleaning it off. Compared to other litter, it’s fairly innocuous if left alone.

Consider this. Most litter flits around untethered and then ends up in landfill or flushed down the sewer and treated by the Public Utilities Commission’s Southeast Wastewater Treatment Plant.

Gum, however, hangs out for a long time, whether it’s naturally or artificially derived. And it’s definitely cheaper to let it linger than to clean it up.

Made of natural or synthetic polymers, a.k.a. plastic, gum quickly becomes nonstick – after the first few unfortunate pedestrians step in it. Moreover, the saliva germs in the gum are neutralized by time and the elements.

Removing it may be more trouble than it’s worth.

The quickest gum remover companies claim it takes six seconds to remove one piece gum. That doesn’t include the time to wipe the sweat out of your eyes, walk to the next piece of gum, move your vehicle, eat lunch, fix equipment, or any number of things. Let’s just say it’s 12 seconds per piece of gum, still a low estimate.

If we assume two million pieces of sidewalk gum that need to be cleaned from the Mission District, at 12 seconds per piece, we get 830 days. Assuming eight hours of gum removal per day and a five-day workweek, no vacation or sick time, that’s more than three years of gum removal. Oh yeah, that excludes gum in the street, on BART plazas, or in parks.

We’re not even talking about the gallons of water,  cleaning solution and electricity. Or the cash.

Maybe it’s better to leave gum on the ground as a reminder of all the trash we discard that gets whisked out of sight. Or to see it as abstract gum art.

The Stuff Left on the Sidewalk.

Pretty much everything gets chewed out of gum and swallowed except the “gum base.” That’s unless the gum chewer swallows the gum, in which case the gum base passes through unchanged and moves on to waste-water treatment. Or so the gum companies and FDA tell us. Hence, gum base is not a food, and companies are free to keep us in the dark on its actual components.

In fact, gum base is proprietary. Gum makers originally used natural rubbery substances like chicle to make the base, but now they employ any number and proportion of natural or synthetic latexes and rubbers.

Maurice’s Corner Liquor Store on 24th Street sells an average selection –  more than 40 kinds of gum. Almost all contain a smattering of the following: gum base, sorbitol, corn syrup, mannitol, natural and artifical flavors – whatever that means – colors, BHT, sucralose, soy lecithin, glycerin, xylitol, acesulfame potassium, hydrogenated starch hydrosylate.

What these do:

BHT – butylhydroxytoluene: a synthetic food additive used as a preservative. It’s unclear whether or not this compound increases your risk for cancer. The Center for Science in the Public Interest suggests avoiding it.

Xylitol, mannitol, sorbitol, hydrogenated starch hydrosylate: these are sugar alcohols – no relation to the kind we drink. They taste sweet but have fewer calories because they aren’t absorbed well. Bacteria don’t generally eat them, so the compounds don’t promote teeth decay or bad breath. Because they’re hard to absorb, these compounds can cause diarrhea if consumed in large quantities.

Acesulfame potassium (acesulfame-K) 200x sweeter than sugar. May be toxic or carcinogenic in large amounts. It’s mixed with other faux sugar to balance the less delightful flavors each chemical has.

Dextrose and corn syrup: corn syrup is made mostly of dextrose, a sugar. It has calories comparable to cane sugar.

Sucralose: (Brand name Splenda) made by reacting sucrose, a natural sugar, with chlorine gas. It’s a low-calorie sweetener. Even though it’s from a natural source, it’s not natural.

Aspartame: some researchers think it probably increases cancer risk. It’s the sweet-tasting, low-cal chemical that makes up Equal and Nutrasweet.

Glycerol: naturally occurring in humans, it tastes sweet and has a viscous texture. It can be used to improve texture and consistency.

Colors and flavors: Proprietary.

A back-of-the-envelope calculation:

I made this estimate by counting the gum blobs in each square of sidewalk I stepped on, measuring every 20 steps. If someone’s done a more scientific calculation, let us know.

So on an average block of Harrison, which has little foot traffic compared to the rest of the Mission, I estimate 5,277 pieces of gum (not gum stains) per block, on the sidewalks of both sides of the street.

Along 24th Street, where many of the sidewalk squares host more than 20 pieces of gum, the numbers are gonna be much higher. Some streets are less traveled than Harrison, so I used the Harrison numbers as a reasonable average. Its blocks are about a tenth of a mile long.

Let’s say 53,000 pieces per mile of street.

53,000 pieces/mile   x   37 miles of street = 1.96 million pieces.

One piece of Wrigley’s Doublemint gum weighs about three grams. It’s maybe 20-30 percent gum base. If Mission Loc@l had a good quality scale, I could estimate by weighing the gum before and after chewing. But we don’t. Feel free to write in though, if you do.

Let’s say one quarter of the weight is gum base and we have 2 million pieces of Wrigley’s gum. I know – we don’t know if they the gum is a big stick or the smaller rectangle or if it has more or less gum base.

But let’s just pretend. That’s 3,300 pounds of gum base on the ground –  more than a ton.

4 Comments

  1. jgregory1

    I fail to understand the attraction of chewing cud like a cow, especially for anybody over 8 years old. More than once I have seen an attractive woman that I was ready to approach at an event, but veered off in another direction that she was working on a piece of gum, making her look like the latest arrival from the trailer park.

  2. jgregory1

    Sorry, bad copying an pasting in first comment. I meant: I fail to understand the attraction of chewing cud like a cow, especially for anybody over 8 years old. More than once I have seen an attractive woman that I was ready to approach at an event, but veered off in another direction when I saw that she was working on a piece of gum, making her look like the latest arrival from the trailer park.

  3. Aida N

    Based on the time it takes to repair potholes in this city, it might be better to just leave the gum in place. At least with gum you have some elasticity in the turf!

    Oh and jgregory, this is not the place to hear about why you are still single.

  4. sfmissionman

    Interesting article. Still, the reporter seems to simply accept that gum is going to be discarded on the sidewalks, as if it came from the sky, as if the chewers had no responsibility to dispose of their used gum appropriately. As if, since it appears to be a cultural norm to chew and toss, it’s OK. Like graffiti, trash, and all the rest of the behaviors which keep the Mission down. Our neighborhood is what we and our neighbors make it, and gum on the sidewalks is emblematic of the larger issue of a relatively low level of civic responsibility.

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