Radioactive Polonium-210 is the most potent carcinogen within tobacco, and it is not intrinsic to the plant. It is a result of past use of phosphate fertilizer

Radioactive Polonium-210 is the most potent carcinogen within tobacco, and it is not intrinsic to the plant. It is a result of past use of phosphate fertilizer [0]. [0] https://www.epa.gov/radtown/radioactivity-tobacco https://www.epa.gov/radtown/radioactivity-tobacco