Where do all the 4000 chemicals in tobacco smoke come from? 

The chemicals in cigarette smoke are from:

i) the tobacco plant

ii) the soil and environment

iii) the manufacturing process

iv) additives

v) burning the tobacco

The tobacco plant

Nicotine is part of the tobacco plant. 

The soil and environment

Tobacco plants absorb various chemicals from the soil and from fertilisers. The chemicals are stored in the leaves and released when the leaves are burned.

These chemicals include cadmium, arsenic and chromium. The leaves can also absorb and concentrate chemicals used in pesticides.

Tobacco plants have large leaves with sticky hairs which can capture chemicals such as radioactive polonium-210 from the atmosphere.  Tobacco builds up higher concentrations of polonium -210 than other plants.

Manufacturing process

Some toxic chemicals derive from the processing of the tobacco and manufacturing of the cigarettes.   When tobacco is cured to remove moisture from the leaves, bacteria produce nitrites that react with chemicals in the leaves. This produces most of the nitrosamines, which are highly carcinogenic, in the end product. Many of these chemicals are only found in tobacco plants. 

Additives

Hundreds of chemicals are added to cigarettes to make them taste better and easier to smoke. This includes, ammonia, an irritating gas which increases the addictive power of nicotine.

Burning the tobacco

Many of the harmful chemicals in tobacco smoke result from the chemical reactions that happen as the cigarette burns. Burning organic material such as tobacco produces polycyclic aromatic hydrocarbons.

Sugars added to cigarettes produce formaldehyde when burned.