Plants Apparently Suffer Risks of Secondhand Smoke Too
Secondhand smoke—which, sometime after I stopped taking health class in my public high school, began to be called “passive smoke”—is a confirmed risk for the loved ones of smokers. A new study from the Technical University of Braunschweig in Germany, however, indicates that it’s not just people who are at risk of absorbing dangerous chemical compounds from nearby smoke. Bizarrely, plants, including the crops we eat, can absorb nicotine from cigarette smoke.
The study, published by the journal Agronomy for Sustainable Development, is singularly odd. Willing souls smoked 11 cigarettes within a two-hour period inside a greenhouse in which peppermint plants were growing. The plants, said Dirk Selmar, the study’s lead author, appeared, at first, to be unchanged. “As far as we have seen, there have been no negative effects on the growth,” he wrote in an email. Yet, tests for nicotine, conducted at various stages in the plants’ life, found that they had “tremendously elevated nicotine levels,” Selmar said.
“In principle, also other compounds could be taken up in the same manner,” he continued. “However, as most components are not volatile, an uptake via the soil is much more likely. We are just looking for the uptake of other alkaloids.”
Tobacco may be the plant most strongly associated with nicotine, but the compound is found elsewhere in the plant world. Eggplant and other nightshades, such as tomatoes and potatoes, contain measurable amounts of nicotine, as does peppermint. But the amounts contained in these plants are significantly less than what’s found in a cigarette. A 1993 study published in The New England Journal of Medicine found that 10 grams of raw eggplant contains the same amount of nicotine as a person would be exposed to by spending three hours in a smoky environment. But unlike tomatoes or peppermint, which both contain less nicotine, eggplant is rarely eaten raw.
Selmar believes the effect of nicotine absorption isn’t limited to plants that already have some level of nicotine naturally. “I am convinced that any plant will take up nicotine, since nicotine will cross the biological membranes,” he said. The team also found that secondhand smoke isn’t the only potential elevator of nicotine levels: Mulching soil with cigarette tobacco, a pest-control measure, also wildly increased nicotine levels in the peppermint plant’s edible leaves.
Nicotine in the soil is less likely now that nicotine-based pesticides, once common in organic farming, have been banned in both the EU and the U.S. But a synthetic version, imidacloprid, is still commonly used and still quite dangerous (it’s considered moderately toxic by the EPA). This study isn’t the first to note that plants can absorb and hold certain toxic materials, but it does drive home that this process can happen in more ways than expected.
Selmar is careful to note that none of the tested peppermint plants had what he considers a level of nicotine dangerous to consumers. The concentration of nicotine is somewhere between 200 and 1,000 times lower in the cigarette-perfumed peppermint than in tobacco. “These values are so low that there is no harm or danger for the consumers,” he said.
But even if it’s not immediately of worry to consumers, it is certainly of interest to anyone who wants to understand how plants work. This is the first time, according to Selmar, that anyone has shown that a compound leached from a decomposing plant (in this case, tobacco) can be absorbed by another plant. That’s the kind of discovery that may not make headlines but will be carefully watched by biologists and more scientifically minded growers, because it could have huge implications for understanding basic traditional methods such as crop rotation. If you plant sorghum after corn, will the rotting corn husks provide beneficial chemicals for the sorghum? Or would it be better to try soybeans or hay instead? Those are the kinds of questions that farmers would love to answer, and the answers could end up providing all of us with more or better foods.