Nicotine: Chemical | Organic composition
Last modified: Saturday, 20. June 2009 - 1:13 pm
Nicotine (C10 H14 N2, beta-pyridyl-alpha-N methylpyrrolidine) is a very poisonous, water- and lipid-soluble, liquid alkaloid with a burning taste. It is colorless, but turns brown and takes on the odor of tobacco upon exposure to air. First isolated in 1828, it is used as an insecticide in agriculture, and as a killer of parasites in veterinary medicine.
Tobacco plant leaves of two species, Nicotiana tobacum and the milder flavored Nicotiana rusticum, generally contain 2-8% nicotine. The average cigarette contains between 8 and 10 mg. Some nicotine is lost from the tobacco leaf during the curing (slow drying in sun, hot air, or smoke), storing, and manufacturing processes. The NCI points out that each can of chewing tobacco holds a lethal dose of nicotine. Also, each tin of snuff delivers as much nicotine as 30-40 cigarettes, with 4.5-6.5 mg nicotine per pinch. Holding a pinch of snuff in the mouth for 20-30 minutes yields nicotine levels two to three times the amount of nicotine delivered by a regular-size cigarette.
Burned tobacco contains some 4,800 distinct chemicals in either gas or particle phases. Many of the compounds in both phases are highly reactive, poisonous, and toxic. Harmful products include oxidants and poisons produced during burning, as well as radioactivity, heavy metals, and pesticides that may have accumulated within the tobacco leaf. Sixty-nine of these substances are known to cause cancer in humans and animals, and many others are known to be strong irritants.
The gaseous phase contains the harmful gases carbon monoxide (CO) and nitrogen oxide, along with carbon dioxide, ammonia, hydrogen cyanide, benzene, toluene, formaldehyde, acetone, acetaldehyde, methanol, and vinyl chloride. CO is a byproduct of the incomplete burning of tobacco and is thought to be a major culprit in causing cardiovascular (heart) disease.
The compounds of the particle phase are collectively called tar, or total particulate matter (TPM). Tar is the oily residue left behind when moisture evaporates from burned tobacco. It contains thousands of compounds, including cancer-causing aromatic amines, nitrosamines, and polycyclic aromatic hydrocarbons that are present in both smoking and smokeless tobacco. Other harmful constituents include radioactive lead and polonium as well as arsenic, among others.
The manufacturers of tobacco products add fillers, flavor enhancers, preservatives, and other additives to make the product more desirable to consumers, especially low-tar brands. Each company’s list of additives was a closely guarded trade secret until 1984, when the lists were submitted to the government. The public was barred from seeing the lists until 1994. The initial list contained 700 potential additives, of which 13 are not allowed in food. One additive, ammonia, may be included to boost the absorption of nicotine and enhance the addictive “kick.” Sweeteners and chocolate may help make cigarettes more attractive to children and first-time users.
Menthol is commonly added to certain brands as it numbs the throat to the irritating effects of smoke. Menthol opens up the lung passages and allows more smoke to be inhaled deeper into the lungs. It makes the lungs more permeable to tars and carcinogens (cancer-causing agents), causing greater disease. These cigarettes also boost nicotine and CO levels. Menthol cigarettes accounted for 26% of the market in 1999.
Low tar and nicotine cigarettes and compensatory smoking
In the 1950s tobacco companies introduced filters on cigarettes to try to remove some of the toxins in smoke. By 1999, 98% of United States smokers used filter-tipped cigarettes. The companies then made other changes to the cigarette to further reduce the amount of tar and nicotine delivered to the smoker. Such changes included altering the composition of the tobacco and adding ventilation holes in the filter to dilute smoke with air. The average tar yield has fallen from 37 mg to 12 mg since 1968. The average nicotine yield fell from 2.7 mg to 0.85 mg.
In theory, filters and other changes to decrease the amount of tar and nicotine in cigarettes should decrease the health hazards of smoking. In fact, the mortality risk among current smokers has risen in the last 40 years even though tar and nicotine levels have fallen. Many smokers of low-yield brands compensate by taking deeper, longer, or more frequent puffs from their cigarettes to get the nicotine their body desires. They may hold the smoke longer in their lungs before exhaling or smoke the cigarette further down. This is referred to as “compensatory smoking.” They may also increase the amount of tar and nicotine taken into the lungs by unintentionally blocking tiny ventilation holes in the filter with their fingers or lips. The smoker may end up inhaling as much or more tar and nicotine as in regular brands. Additionally, low tar products may also have higher levels of CO, and a variety of other toxins.
Kreteks and bidis
Increasing numbers of teens are turning to alternative cigarettes called bidis, tiny flavored cigarettes from India, and kreteks or clove cigarettes from Indonesia. Bidis (or beedies) are small, unfiltered cigarettes, handrolled in leaves. Flavorings such as chocolate, strawberry, and vanilla are added to the American versions of bidis to make them more appealing to minors. Bidis contain more than three times the amount of nicotine and five times the amount of tar than regular cigarette smoke. They are also puffed more frequently than regular cigarettes to prevent them from going out.
Kreteks contain tobacco and 40% shredded clove buds. They have a pleasant, sweet aroma of cloves, but have such high levels of tar, nicotine, and CO, that smoking one is equivalent to smoking 20 light American cigarettes. Eugenol, the local anesthetic in cloves, permits the inhalation of the harsh smoke.
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