this is what I found. i copy and pasted it from my yahoo search.
Often hobbyists are worried about the effects of nicotine and tar that enter the air as a by-product of cigarette, pipe and cigar smoking, and transfer to the water, as we have seen in the airborne pollution section.
The dangers associated with such compounds are real, but are completely neutralized by the use of Poly Filters and/or activated carbon. They should not be a cause for concern if chemical filtration is used, especially if you also pre-filter the air that your pump blows into the filter and into the water.
Cigarette butts thrown in your tank, for example while you have guests, will however do considerable damage