12.3 Chemicals and contaminants in tobacco products

Last updated: January 2022
Suggested citation: Winnall, WR. 12.3 Chemicals in and contaminants in tobacco products. In Greenhalgh EM, Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2022. Available from https://www.tobaccoinaustralia.org.au/chapter-12-tobacco-products/12-3-chemicals-and-contaminants-in-tobacco-products  

 

Many people who use tobacco products may be surprised to learn that they contain thousands of chemicals. The processing of tobacco plants and manufacture of cigarettes and other tobacco products involves multiple steps in which chemicals are added or formed anew in chemical reactions. Raw tobacco plants themselves contain naturally occurring chemicals, some of which are highly toxic. The tobacco products made from these plants contains thousands of natural and synthetic chemicals, many of which are toxic and are known causes of cancer and other diseases.

This section describes the routes by which chemicals enter tobacco products and the types of chemicals present. The focus of this section is on the chemicals present before a tobacco product is used – before emissions are produced by burning, heating or chewing. Section 12.4 describes the chemicals detected in tobacco emissions and provides greater detail on the chemicals that are of most concern. Chemicals in tobacco are described further in Section 12.6 (additives and flavours) and Section 12.7 (menthol).

Harmful chemicals follow many different routes of entry into the final tobacco product. Some are naturally produced by the plant; others are added in fertilisers and pesticides; some are produced in chemical reactions that occur during the curing and aging of tobacco; others are additives and chemicals that produce flavours. Some are present in the filter, dyes or paper wrapper (see Section 12.8).

Although much of the research and rhetoric on the chemicals in tobacco centres on those that cause harm, there are other types of chemicals that are pertinent to tobacco control. Specific chemicals in tobacco contribute to the attractiveness of the product (such as flavours and aromas) as well as the addictiveness of the product (such as nicotine).

12.3.1 Chemicals from the tobacco plant

Tobacco plants naturally produce biological chemicals and absorb substances from the soil and air. These chemicals contribute to the attractiveness (through flavour compounds such as polyphenols), addictiveness (through nicotine and other alkaloids) and toxicity (such as toxic metals) of tobacco products. Therefore, tobacco products that are labelled ‘natural’, ‘organic’ or ‘free from additives’ still contain many harmful substances that come from the plants themselves, as well as from the manufacturing process and from the burning of tobacco products.

Nicotine, the main addictive chemical in tobacco products, is naturally produced by the tobacco plant. Nicotine acts as a natural pesticide in these plants due to its toxicity to many insects and other pests. Nicotine has been used as an agricultural pesticide in the past.1 It is mainly produced in the leaves of the plant, and the amount of nicotine in tobacco leaves depends on factors such as the position of the leaf on the stalk, the degree of ripening and the fertiliser treatments used.2 ,3

Nicotine is an alkaloid— a naturally occurring basic (i.e. non-acidic) compound containing nitrogen atoms.4 Similar alkaloids are also made by tobacco plants, including anatabine, anabasine, and nornicotine. These other alkaloids may also have pharmacological effects on humans and may contribute to the addictiveness of tobacco products, depending on their concentration in the final product.2 Nicotine itself is not a carcinogen—a compound that mutates genes to cause cancer. However, nicotine, and other alkaloids in tobacco plants, serve as precursors for the production of carcinogenic nitrosamines that are present in tobacco products and their emissions2 (see below Section 12.3.3 and Section 12.4.3.7). See Section 12.4.3.1 for more information on how nicotine causes addiction.

Tobacco plants contain natural compounds such as polyphenols that may contribute to the flavour of the tobacco. Polyphenols found in tobacco include rutin, chlorogenic acid, caffeic acid and scopoletin.5

Tobacco plants also contain toxic metals. Cadmium and lead are found at relatively high levels in tobacco leaves because the plants readily absorb them from soil. They may also be absorbed from the air around the tobacco plants.2 ,6 Radioactive polonium-210 is found in tobacco leaves, entering via the soil and possibly through the air.7 ,8 Despite knowing about the presence of polonium-210 for decades, tobacco companies suppressed publication of their internal research demonstrating this, to avoid public awareness of the issue.9

Arsenic, beryllium, cadmium, chromium, manganese, cobalt, nickel and mercury are all detectable in cigarettes.10 ,11 Cadmium, lead, nickel, arsenic and chromium have also been found in smokeless tobacco products.12 ,13 Tobacco products such as cigarettes, smokeless tobacco products, roll-your-own and pipe tobacco and little cigars in the US have detectable levels of aluminium.14 Unfortunately, there is little information on the routes of entry of these chemicals into tobacco products. However, soils in which tobacco plants are grown in China have been shown to contain arsenic, cadmium, chromium, mercury, nickel and lead that may have come from fertilisers or from the atmosphere.15 Some illicit tobacco has been shown to contain even higher levels of toxic metals, coming from overuse of fertilisers.16

The maturity of a tobacco plant when harvested and the geographical location of its growth may affect the chemical composition of the plant, such as the nicotine content, the polyphenols content, such as rutin and quercetin (that contribute to the taste of the smoke) and proportion of fat-soluble compounds.17 The geographical region where a tobacco plant is grown may also affect the levels of various sugar molecules, amino acids and other types of acids in the plant.18

12.3.2 Chemicals from fertilisers and pesticides

Tobacco is a crop that requires intensive use of pesticides such as insecticides, herbicides and fungicides.19 ,20

Tobacco crops require standard agricultural fertilisers that deliver nitrates, phosphates and potassium to promote growth.21 Nitrates added from fertilisers affect the amount of nitrosamines produced during later stages of tobacco processing (curing, aging and storage of tobacco).2 Nitrogen from fertilisers can also affect the amount of aromatic amines present in the tobacco.2 Many nitrosamines and some aromatic amines from tobacco are carcinogenic2 (see Section 12.4.3.3 and 12.4.3.7).

High phosphate fertilisers used for tobacco plants are also a source of radioactive polonium-210 and lead-210. These fertilisers contain radium-226, which breaks down into lead and polonium isotopes.9 Fertiliser may be a source of toxic metals in the soil that are taken up into growing tobacco plants (see Section 12.3.1).

Pesticides used for tobacco crops in low- and middle-income countries include organic pesticides such as dichlorodiphenyltrichloroethane (DDT) and 11 other persistent organic pollutants that are banned in high-income countries.20 Pesticides such as phosphine and methyl bromide may also be used to protect stored tobacco (raw or processed) from moths and beetles.19 ,22 Trace amounts of pesticides remain on tobacco leaves and can be found in the final tobacco products.19 ,23-25 The process of burning tobacco does not completely destroy these chemicals, as pesticide residues are also found in cigarette smoke, leading to human exposure when the smoke is inhaled.25 ,26  

The tobacco industry has actively avoided disclosing information to consumers regarding pesticide levels in cigarettes and other tobacco products.19 ,26 Industry documents show that, despite knowing its tobacco was contaminated with pesticides such as high levels of organochlorine, between 1972 and 1994, Philip Morris Australia did not advise Australian consumers of this contamination.26 The tobacco industry does not disclose the range of pesticides to which Australian tobacco consumers are being exposed.

12.3.3 Chemicals and contaminants from the curing and aging of tobacco

After harvest, tobacco plants are cured and aged. Curing refers to drying, which can be achieved in a variety of ways (see Section 12.1.1). Aging, either after harvest or after curing, may occur over months or years, leading to further changes in the chemical composition of the tobacco plants (see Section 12.1.2).

Nitrosamines, including tobacco-specific nitrosamines (TSNAs), in tobacco products are of particular concern due to their carcinogenic (cancer-causing) activity. These compounds are not present in raw tobacco leaves. Nitrosamines are formed by modification of alkaloids, such as nicotine, during the curing and aging of tobacco, and may also be formed during tobacco combustion.2 ,27 The amount of nitrogen fertiliser used for plant growth is associated with the levels of nitrosamines in the tobacco smoke.2 The variety of tobacco plants is also associated with the amount of nitrosamines in the final tobacco product. Oriental variety tobacco contains the lowest levels of TSNAs whereas Burley tobacco contains the highest levels.2

Specific flue-curing methods also contribute to TSNA levels in tobacco.28 From the 1970s until the early 2000s, most producers in the US and Canada cured tobacco using direct heating, where the tobacco was directly exposed to exhaust gases from natural gas and propane fires. This practice led to an increase in the TSNAs in the tobacco. Smokers were therefore exposed to unnecessarily high levels of TSNAs for 30 to 40 years. Since the start of the 21 st Century, tobacco producers have been changing their curing methods to reduce the amount of TSNAs in tobacco products. However, they have demanded public money to offset their costs of modifying kilns to reverse the damaging changes they made in the past.28

The types of microorganisms growing on air-cured Burley tobacco may affect the levels of TSNAs produced during the curing process. Researchers have shown that with increasing humidity during the curing of Burley tobacco, there are higher proportions of bacteria in the Firmicutes and Actinobacteria phyla and increased levels of TSNAs in the cured tobacco.11

12.3.4 Contamination of tobacco products with microorganisms

Tobacco plants harbour numerous microorganisms during their growth, such as bacteria and fungi (moulds and yeasts). Microorganisms also grow in tobacco during curing and storage.29 At least 89 bacterial genera and 19 fungal genera have been isolated from the tobacco in cigarettes and other tobacco products. These include the bacteria genera Bacillus, Pseudomonas, and Staphylococcus, and the fungi Aspergillus, Penicillium and Candida.29 Living bacteria have also been detected inside the filters of smoked cigarettes.30 Chemicals released from bacteria that have been found in tobacco smoke, such as lipopolysaccharides and peptidoglycans, can be harmful to human health. Further research is required to determine whether viable bacteria or fungi from tobacco products enter the lungs of smokers, and the health consequences of these microorganisms for consumers.29

The types of microorganisms growing on tobacco leaves during curing may affect the levels of TSNAs produced during the curing process (see Section 12.3.3).

12.3.5 Additives and flavours

A range of chemicals are added to tobacco during the manufacture of tobacco products for a variety of reasons. Additives and flavours are described in Section 12.6 and menthol in Section 12.7.

 

Relevant news and research

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References

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