There are many environmental factors that contribute to cancer and have been identified as carcinogens. Among these are certain chemicals that are known to potentially increase the risk of cancer. These include:

• Asbestos. A group of naturally occurring fibrous minerals found in soil and rocks in many parts of the world. Because asbestos fibers are resistant to heat, they have been used as an insulating material for centuries. However, it is now recognized that inhaling or ingesting asbestos fibers can trigger diseases such as lung cancer (with added risk from smoking) and mesothelioma, a rare cancer that affects the thin membranes lining the abdomen and chest. It also can result in scarring of the lungs. Evidence suggests that asbestos exposure may contribute to stomach cancer, colon cancer and cancer of the larynx. The IARC has classified asbestos as carcinogenic to humans (Group 1).
  
  
• Arsenic. A naturally occurring toxic chemical used in pesticides, as a wood preserve and in the manufacture of products including dyes, paints, medicines, soaps and semiconductors. Workplace exposures are known as occupational risk factors. Arsenic can also be found in drinking water, soil, air and food. It has been linked to cancers of the bladder, lung, kidney, liver, nasal passages, prostate and skin (Group 1).
  
  
• Benzene. A colorless, flammable liquid with a sweet-smelling odor that is inhaled or is absorbed through the skin. Benzene is primarily used as a solvent, as a starting material in the synthesis of other chemicals and as a gasoline additive. Workplaces are the most common site of exposure to high levels of benzene, especially for people who work in the rubber industry, oil refineries, chemical plants, shoe manufacturing sites and gasoline-related industries.
  
  People are regularly exposed to lower doses in the general environment due to gasoline, automobile exhaust fumes, cigarette smoke and emissions from coke ovens. It canbe found in industrial processes and wastewater from certain industries. Benzene is also found in glues, cleaning products, detergents, art supplies and paint strippers.
  
  Benzene appears to contribute to acute myeloid leukemia (AML). It can be measured in the blood and the breath. Quitting smoking can dramatically reduce the levels of benzene in a person’s blood. People should also avoid gasoline fumes by pumping gasoline carefully and choosing gas stations with vapor recovery systems that capture fumes (Group 1).
  
  
• Vinyl chloride. A chemical used in the manufacture of plastics. According to the American Cancer Society, exposure to vinyl chloride increases the risk of liver cancer, lung cancer and possibly other cancers (Group 1).

Other chemicals have also been associated in cancer. In some cases, the links between the chemicals and cancer are suspected, but not yet confirmed. These chemicals include:

• Lead. A bluish-gray metal found in small amounts in the earth’s crust that is also found in plants, animals, air, water, dust and soil. Lead is an indestructible element that persists once released into the environment. It can move from one medium to another. Exposure to lead can occur from swallowing or inhaling it, with known toxic effects in the human body. Lead is a suspected factor in cancers of the lungs, brain, stomach, kidneys and colon. Although it is not proven that lead contributes to cancer, the IARC classifies it as possibly carcinogenic to humans (Group 2B), and the EPA considers it a probable carcinogen in humans.
  
  
• Methyl tertiary-butyl ether (MTBE). Part of a group of chemicals known as fuel oxygenates, which are added to increase gasoline’s oxygen content. Federal legislation in the early 1990s required oxygenates to be added to gasoline to make it burn better and to decrease carbon monoxide and other vehicle emissions. However, MTBE is more soluble in water than most gasoline components and is more resistant to biodegradation. As a result, it has begun showing up in detectable amounts in the air and drinking water of many communities. It is not known whether or not MTBE causes cancer in humans, but it has been shown to cause lymphomas and leukemias leukemias in laboratory animals. Some of these animals also have developed cancer of the kidneys, liver, testicles and uterus. The IARC considers MTBE to be unclassifiable as to carcinogenicity in humans (Group 3), and use of MTBE is being phased out.
  

There are some chemicals that, although suspected, have not been positively linked to cancers in epidemiological studies, including:

• Aspartame. A low-calorie artificial sweetener about 200 times sweeter than sugar that once was suspected of causing brain cancer. It can be found in tabletop sweeteners, foods and beverages. In the early 1980s, the Food and Drug Administration (FDA) approved aspartame for use in many products, including breakfast cereals, chewing gum, dry beverage mixes, carbonated beverages, instant tea and coffee, gelatins and puddings.
  
  Recent studies appear to have discredited the theory that aspartame causes cancer. The FDA, World Health Organization and other organizations have declared aspartame safe for use for most individuals, with the exception of people with the genetic disorder phenylketonuria. These individuals cannot metabolize the amino acid phenylalanine, which appears in aspartame.