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Since I'm burdened with dial-up internet speed, I don't have the patience to track down the exact info. A while back a study from a university came out stating that from the years 1998 to 2002 the amount of nicotine in cigarettes increased 10%. The tobacco companies blamed it on the tobacco crops they were using.
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I found the article on "The Official Website of the Commonwealth of Massachusetts":
http://www.mass.gov/Eeohhs2/docs/dph..._factsheet.pdf
.... and it has been used / picked up by a ton of other agencies and organizations including the Washington Post...