Note that they obviously don't have 50-100 rads in them (enough to burn your skin) but they do have enough to cause irregular cell growth. And even though the tobacco itself may be chemically unaltered, the only commercial fertilizer used for tobacco (note that ALL American tobacco companies use this fertilizer as it is the only thing that can put enough nitrogen in the soil to grow proper tobacco) is a Phosphate based on apatite, apatite rock has a couple nasty radioactive isotopes floating around in it's composition including radium, polonium, and radioactive lead (Lead-210). Since tobacco kills soil and depletes it quickly, most N enhancing fertilizers simply won't do the trick and inferior (or dead) tobacco is the result. Even though the radioactivity in cigarettes is only a bit higher than the levels of background radiation in your everyday life, but since it is being exposed to the soft, fragile tissue in your lungs and possibly bloodstream due to smoke related lesions (which cannabis smoke also causes) you are put at a very high risk for developing cancer.