Your Spice Cabinet Needs to Quit Smoking

Smoking is bad for you. This is not a secret.

Nor is it news that smoking can be just as bad for people who happen to breathe in the vicinity of a smoker's toxic exhalations. And recently, scientists have become increasingly concerned about another form of passive smoking, known as third-hand smoke: the collection of carcinogenic byproducts of smoking that stick to walls, upholstery, and even the dashboard of your car.

But people and plush chairs aren't the only things that absorb smoke. Plants meant for food do, too.

The problem is, no one's exactly sure how it gets there in the first place. While nicotine was once used as a pesticide, it has since been banned in both the EU and the US. Recently, a study published in the journal Agronomy for Sustainable Development sought to discover the origins of nicotine that has increasingly been found in food crops such as spices and herbal teas.

The researchers, led by Dirk Selmar at the Technical University of Braunschweig, Germany, sought to figure out why so many food plants contain high levels of nicotine, even when pesticides containing them have been out of use for a number of years. While some people simply assumed that farmers were using illegal, nicotine-based pesticides, they thought the nicotine could be coming from somewhere else.

To begin, they needed to pick their crops. The researchers ruled out plants that have naturally naturally high levels of nicotine (though much, much lower than tobacco), like potatoes, tomatoes, and eggplants.

Selmar and his team decided to experiment with peppermint plants, which naturally contain only trace levels of nicotine. They grew one group of plants in nicotine-enriched soil—that is, soil mulched with commercial cigarette tobacco. (It was even that fancy American Spirit tobacco that smokers tell themselves is healthier than typical coffin nails.) The other plants were raised in a greenhouse in which 11 cigarettes were smoked over the course of two hours.

When the researchers sacrificed the plants and analyzed their nicotine content, they found that they had all absorbed massive amounts of nicotine compared to their control groups. Plants mulched with tobacco had "a tremendous increase in nicotine concentration," the authors wrote. The uptake was dose-dependent, too—meaning that the more tobacco there was in the soil, the more nicotine the plants sucked up. Worryingly, they also discovered that dead plants can transfer alkaloids like nicotine to living plants.

The fumigated plants fared just as poorly. After being exposed to a half-pack's worth of smoke in a short time, the plants contained nearly 1,000 times the "maximum residue level" set by EU food authorities.

The good news is that the nicotine concentration in the plants decreased—but did not disappear—over time. The researchers were able to rule out evaporation, hypothesizing instead that the plants had simply metabolized some of the nicotine. That would make some sense, since peppermint already produces small amounts of nicotine on its own.

The study authors don't suggest possible sources of nicotine-laden soil or cigarette smoke, though one could guess that a lack of outdoor smoking regulations on farms—such as in Minnesota—certainly doesn't keep farm workers from lighting up around the crops. And if there's at least one takeaway for green thumbs at home, it's this: Don't use your herb garden as an ashtray.