BERLIN : Passive smoking is not only harmful to humans, it also affects plants which can take up nicotine from cigarette smoke and contaminated soil, according to a new study.
The findings may explain why high concentrations of nicotine are often found in spices, herbal teas and medicinal plants, despite the fact that this alkaloid is no longer permitted in insecticides, researchers said.
Previously, nicotine was frequently used as an insecticide until it was banned by the European Union in 2009 because of its toxicity, researchers said.
However, a large number of food crops and plant-derived products still contain very high levels of nicotine.
Dirk Selmar and colleagues at the Technical University of Braunschweig, Germany, wanted to find out whether there are other reasons at play than the possible illegal use of nicotine-containing insecticides.
They used peppermint plants (Mentha x piperita), which contain minimal traces of nicotine, in a series of mulching and fumigation experiments.
“Tremendously elevated nicotine levels were detected after fumigation with cigarette smoke,” said Selmar.
Selmar’s team is also the first to show that peppermint plants can actually take up high concentrations of nicotine from contaminated soils.
The team analysed plants in soil mulched with cigarette tobacco for more than nine days to find that the resulting nicotine concentrations in them were several times higher than the maximum residue level set by European authorities.
The researchers found a drastic decrease in nicotine concentration as time progressed. This is likely because the nicotine is taken up by the roots of the peppermint plants and processed in their leaves.
“Our results suggest that the widespread occurrence of nicotine in medicinal, spice and food plants may, at least in part, be due to other nicotine sources apart from the illegal use of insecticides,” said Selmar.
Researchers said the results have a tremendous relevance for basic science: they prove that substances, such as alkaloids, can be transferred from one plant, after its death, to another.
Such “horizontal transfer of natural products” sheds light on the hitherto unexplained success behind farming practices such as crop rotation and the co-cultivation of certain vegetables, researchers said. (AGENCIES)
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