climate and come mostly from Turkey, Greece, Yugoslavia, Bulgaria, and Russia. They are cultivated with little fertilizer. Oriental tobaccos have mild, aromatic smoke and low nicotine content.

Cigarettes, cigars, and smokeless products use blended tobaccos. The largest component of most cigarette blends in the United States is Bright tobacco (Browne, 1990). Blends are made to achieve specific pH, taste, burning characteristics, and nicotine content. The type of tobacco blend found in cigarettes significantly affects the pH, nicotine content, and toxicity of the smoke produced. The blend can be manipulated by a choice of 60 species and 100 varieties of tobacco. Almost all commercial tobacco products, however, use N. tabacum species and a small amount of N. rustica in some specialized tobacco products. Cured tobacco lines can contain between 0.2 and 4.75% nicotine (depending on plant genetics, growing conditions, and place of harvest from the stalk; NIH, 1996).

In addition to tobacco leaf, reconstituted sheet tobacco is also used in most commercial products. Cigarettes primarily made with reconstituted tobacco deliver lower smoke yields of tar, phenols, and benzo [a] pyrene (NIH, 1996). Reconstituted tobacco sheet is also used for economic reasons and for the introduction of additives that change various characteristics of the cigarette. Reconstituted tobacco results from a process that combines stems, leaves, and tobacco scrap into a slurry or from making a tobacco “paper,” which is cut (Browne, 1990).

Another alternative to leaf tobacco is puffed, expanded, or freeze-dried tobacco (Hoffman and Hoffman, 1997; NIH, 1996). Less tobacco is therefore needed to fill a cigarette while still providing a sensation of fullness and substance in the smoke. While tobacco is being cured, it loses some of its integrity through water loss. Expanding tobacco increases its filling capacity in the final tobacco column of the cigarette by primarily restoring the original cellular structure. This process is performed by expanding the cells with water, steam, and various organic or inorganic fluids depending on the manufacturers patent (David and Nielsen, 1999; NIH, 1996).

The pH strongly influences the concentration of free nicotine in tobacco smoke. The pH is influenced by the type of tobacco used, as well as by the addition of ammonia to the manufacturing process. Free nicotine has a greater effect on the sensory nerves in the mouth and throat than protonated nicotine, which contributes to the impact or strength of the cigarette. Free nicotine is absorbed more rapidly than protonated nicotine across mucous membranes. The phenomenon of more rapid absorption of nicotine at higher pH has been documented in people using different brands of smokeless tobacco. Free nicotine is absorbed through the mouth from alkaline pipe, cigar, and dark cigarette smoke, but not from acidic smoke of blonde tobacco cigarettes. Free nicotine may be absorbed more



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