I don't know if this is totally true or not, but what about the use of polonium-210 and lead-210 in the fertilizer. Those substances are radioactive, which could be causing the cancer.

Erowid Tobacco Vaults : General Info
NothingMoreThenTruth Reviewed by NothingMoreThenTruth on . Does Nicotine really vaporize? Okay, well yesterday I made one of those retarded lightbulb vapes. Having no weed, I decided I would see if it was airtight using some pipe tobacco I had lying around. I held my zippo under it for about 30 seconds, and a swirly mist filled the bulb. I sucked in (it seemed pretty airtight btw) and felt nothing at all, all I got was the vanilla-y taste from the flavored tobacco. So I'm wondering if the nicotine actually vaporizes, or if I need to keep the lighter going for longer to Rating: 5