The different types of potential carcinogens cover a wide range and include both organic and inorganic compounds, radiation exposure from natural or man-made source materials, and living organisms. Any agent that can contribute to cell mutation has the potential to lead to cancer and can be classified as a carcinogen. This often includes many materials that may be harmless in small concentrations, or harmless in the absence of other chemicals that act as triggering agents.
Among synthetic chemicals, dioxins have been called the most toxic chemical compound ever produced by man, and are a byproduct of bleaching in paper mills, from the production of agricultural fertilizers and insecticides, and from incineration. The single smallest, microscopically detectable levels of dioxin have been shown to cause cancer in laboratory animals. Modern industrial processes in the US produce 1,200 pounds (544 kilograms) of dioxin each year, where 12 pounds (5.4 kilograms) alone is enough to count as a lifetime dose for 500 million people. Estimates are that the average American, European, or Canadian already has enough dioxin in his or her body to equal levels that have demonstrated adverse health effects in laboratory animals. Dioxins also act as a cancer enhancer, increasing the intensity of other carcinogens, and are known to contribute to dozens of types of cancer, from skin and liver cancers to Hodgkin's disease.
The most potent natural carcinogen is thought to be Aflatoxin B1, which is produced by the fungus Aspergillus flavus that often grows on grains and nuts such as peanuts stored in hot, humid environments. Found in rice, soybeans, corn, and wheat as well, it is a potent liver carcinogen causing Heptocellular carcinoma, which will kill almost every patient that contracts it within one year. It causes cancer by attacking the p53 gene in humans, which works as a tumor-suppressing gene.
Radionuclide and radiation sources are also carcinogens. One of the most common, widespread carcinogens in this category is radon gas, which is naturally emitted from trace elements of uranium in soil. Radon gas is the second leading cause of lung cancer in the United States after cigarette smoking, killing an estimated 15,000-22,000 people per year. The World Health Organization estimates that radon gas exposure accounts for 6%-15% of all cases of lung cancer worldwide.
Thousands of other potential carcinogens exist in nature and as a direct and indirect result of human industrial processes. Tobacco smoke is known to contain 43 carcinogenic agents, and benzene vapors in gasoline can lead to immune system breakdowns causing leukemia. Dozens of potent carcinogens exist as organic compounds in the average turkey dinner Americans eat for the Thanksgiving holiday. Carcinogens are also found in many cosmetics, as well as in synthetic food preservatives, additives, and coloring agents in the food supply. It is essentially impossible to avoid contact with all carcinogenic agents, but, with thoughtful effort and planning, exposure can be greatly minimized.