Additives and contaminants are often components of commercially grown, prepared, or packaged foods. Noncommercially grown food can also become contaminated due to pollution or pesticides.
Substances, such as preservatives, emulsifiers, antioxidants, and stabilizers, are often added to a food to do the following:
Enable it to be processed more easily
Preserve it longer and reduce spoilage
Prevent contamination by microorganisms and thus prevent food-borne disorders
Improve taste, add color, or enhance its aroma, making it more appealing
In commercially prepared foods, the amount of additives that can be included is limited to that shown to be safe by laboratory tests. However, weighing the benefits of additives against the risks is often complex. For example, nitrite, which is used in cured meats, not only improves flavor but also inhibits the growth of bacteria that cause botulism. However, nitrite converts to nitrosamines, which can cause cancer in animals. On the other hand, the amount of nitrite added to cured meat is small compared with the amount of nitrates that occurs naturally in food and that is converted to nitrite by the salivary glands.
Rarely, some additives (such as sulfites) may cause allergic reactions. Sulfites, which occur naturally in wines, are added to such foods as dried fruit and dried potatoes as a preservative.
Foods may be contaminated because the air, water, and soil are polluted, for example, by heavy metals (such as lead, cadmium, and mercury) or PCBs (polychlorinated biphenyls). PCBs used to be used as coolants and in many other products and are now present in the air, soil, and water in many places.
Foods may be contaminated by pesticides or packaging materials or during cooking or processing. In addition, so-called endocrine-disrupting chemicals in the environment (such as some insecticides, petrochemicals, and industrial solvents) can affect the body's endocrine system and alter hormone levels, causing alterations in sex organs, immune function, nervous system function, growth and development, and certain cancers; they may also promote obesity.
Foods may also be contaminated by drugs (such as antibiotics and growth hormone) that are given to animals.
Sometimes limited amounts of contaminants are allowed in foods because the contaminants cannot be completely eliminated without damaging the foods. Common contaminants include
Nitrates (in green leafy vegetables)
Aflatoxins, produced by molds (in nuts and milk)
Growth-promoting hormones (in dairy products and meat)
Levels that have not caused illness or other problems in people are considered safe. However, determining whether a small amount of a contaminant has caused a problem is very difficult. Thus, safe levels are often determined by general agreement rather than by hard evidence. Whether problems can result from consuming a small amount of some contaminants over a long time is unclear, although with very tiny amounts, such problems are unlikely.
Foods may contain animal hairs, animal feces, and insect parts in such tiny amounts that removal is impossible.