Aqueous extract makes a nifty corrosion inhibitor

By Janet Raloff

Web edition: May 12, 2010

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Butts wanted

Usually considered trash, these look like an untapped resource to some chemists.

Credit: iStockPhoto

People smoke a lot of cigarettes, which leads to a lot of trash. Tom Novotny has done the math: An estimated 5.6 trillion butts each year end up littering the global environment. But a group of Chinese researchers has a solution: recycling. Their new data indicate that an aqueous extract of stinky butts makes a great corrosion inhibitor for steel.

Jun Zhao and Ningsheng Zhang of Xi’an Jiaotong University and their colleagues soaked cigarette butts that they had retrieved from trash or along the side of roads in distilled water for 24 hours. Each 100 milliliters got five butts. Then they added some of this cigarette extract to a 10 percent solution of hydrochloric acid, which would ordinarily pit and corrode the steel. But the amount of corrosion dropped by almost 95 percent when another 5 percent  of the solution consisted of the butt extract.

If the researchers upped the strength of the acid, they needed to also increase the amount of added cigarette extract. For instance, with a 20 percent hydrochloric acid solution, the researchers needed to increase the butt leachate to 10 percent of the liquid to keep damage to the steel low: at less than 12 percent of the corrosion seen with the unamended acid solution. The researchers shared their findings last month in Industrial & Engineering Chemistry Research.

In the paper, they describe a series of chemical tests to home in on some likely contributors to the corrosion inhibition. Nine stood out. They included (in descending order) nicotine, continine, N-nitroso-nornicotine and other compounds that tended to have very long, unwieldy monikers.

Novotny, an epidemiologist at San Diego State University's School of Public Health, has heard lots of putative uses for cigarette butts. Like using them as filler for construction bricks. But what he’d prefer to see would be vastly fewer smokers. Or at least a ban on cigarette filters.

“I realize that might sound strange,” he says, but filters don’t protect the smoker from toxic constituents of a burning cigarette. “On a population basis,” he says, data show that “the filter has no effect on lung cancer or heart disease.” What these little cellulose-acetate caps do is persist in the environment. And they tend to show up where people are. Like on streets and the beach.

“We did a cleanup on our campus, a couple weeks ago,” Novotny says. “And in one hour, 60 volunteers picked up 24,000 cigarette butts.” Each with its own nondegrading filter, he says. During beach cleanup programs, butts account for 23 to 30 percent, by number, of the pieces of litter collected each year, he says.

One study in San Francisco tallied the cost of cleaning up butts and cigarette packaging from city streets. It averaged 20 cents per pack of cigarettes that had been sold in the city. Last summer, San Francisco passed a litter-fee surcharge of 20 cents per pack of cigarettes (although it is currently being challenged in the courts by the cigarette industry).

But these butts constitute far more than litter, Novotny argues. They’re actually toxic waste, he says, a share of which invariably enters streams. A study that his team conducted last year showed that all it took was a single cigarette butt to kill half of the fish in a liter of water. The toxicity held for both a freshwater species (fathead minnow) and saltwater fish (top smelt).

The tobacco appeared responsible because when the researchers snapped the filters off and just incubated fish with these caps, it took four filters to kill half of the fish in that liter of water. In this case, the filters apparently served as tiny toxic reservoirs for some of the tobacco's combustion residues that had passed through them.

Details of the study, reported last November in Philadelphia at the American Public Health Association annual meeting, are due to be published later this year in a special supplement of Tobacco Control.

“We did not have the funding to do sophisticated testing of the [butt] leachates during that study and find out what precisely was killing the fish,” Novotny says. “But we’re now planning that in our next round of research.”

Fine. But I still like the Chinese idea of turning a toxic waste into a valuable raw ingredient. At a minimum, it might encourage more organizations to collect those butts, rather than ignoring them on the street where they almost certainly will leach some of their toxic chemicals and heavy metals.