It has been estimated that every year, 4.5 trillion cigarette butts are added to the world’s ecosystem. That would be bad enough if they were simply disgusting, but when they’re left on beaches or washed down storm sewers, they can be lethal to fish. Unfortunately, there’s nothing that can be done with the butts, other than throwing them out... until now, perhaps. Researchers from China’s Xi’an Jiaotong University claim that cigarette butts can be used to make an excellent rust inhibitor.

The scientists collected butts from garbage bins and roadways, and soaked them in distilled water - the ideal combination was five butts aged in 100 mL of water for 24 hours. The cigarette butt water extract was then added to a hydrochloric acid solution, and applied to discs made from N80 steel, a type commonly used in the oil industry. The treated discs, it turned out, were remarkably resistant to rust. Depending on the extract concentration, rust inhibition of up to 94.6% could be achieved.

So just what is it about cigarette butt water that rust doesn’t like? Nine chemicals in the extract were identified as possibilities, nicotine being the most prominent. It’s possible, the researchers say, that the oxidants in the extract could react with the steel’s iron atoms, creating an insoluble “oxidation film” on the steel’s surface.

The Xi’an Jiaotong teams' complete report was recently published in Industrial & Engineering Chemistry Research.