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In the most recent version of the National Toxicology Program’s Report on Carcinogens, two new substances have been classified as “known human carcinogens” and six others have been classified as “reasonably anticipated to be human carcinogens.”

The National Toxicology Program is headquartered at the National Institute of Environmental Health Sciences, part of the National Institutes of Health. The NTP’s Report on Carcinogens—now in its 12thEdition—provides information about substances that are known or reasonably anticipated to cause cancer in humans.

The following two substances were added to the list of known human carcinogens (factors known to cause cancer in humans):

  • Formaldehyde: Formaldehyde was first listed in the 2nd Report on Carcinogens as a substance that was reasonably anticipated to be a human carcinogen. Newer evidence from studies in humans shows that higher levels of exposure are linked with an increased risk of certain types of cancer such as nasopharyngeal cancer, sinonasal cancer, and myeloid leukemia. Formaldehyde is commonly used to make resins for household items, and is also used as a preservative by medical laboratories and mortuaries. Formaldehyde may be found in some consumer products, including some hair-straightening products.
  • Aristolochic acids: Aristolochic acids occur naturally in some plant species. Consumption of botanical products that contain aristolochic acids has been linked with high rates of bladder or upper urinary tract cancer in people with kidney disease. In 2001, the U.S. Food and Drug Administration advised consumers not to use botanical products that contain aristolochic acids, but these products are still available online and in other countries. Aristolochic acids may also be found as a contaminant in some herbal products.
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The following six substances were added to the list of substances that are “reasonably anticipated to be human carcinogens”:

  • Captafol: A fungicide that has been banned in the U.S. since 1999. Past exposures may affect health. Captafol was used to control fungal diseases in fruits, vegetables, ornamental plants, and grasses. Studies in experimental animals suggest that it may case cancer at several different sites.
  • Cobalt-tungsten carbide: Used to make cutting and grinding tools, dies, and wear-resistant products for several types of industry. There is some, limited evidence of a link with lung cancer in workers involved with cobalt-tungsten carbide hard metal manufacturing.
  • Certain inhalable glass wool fibers: Added to the list based on animal studies. Not all glass wool products were found to be carcinogenic. The glass wool fibers referred to in the report are those that can enter the respiratory tract, are highly durable, and remain in the lungs for long periods of time.
  • O-Nitrotoluene: Used in the preparation of some dyes, agricultural chemicals, rubbers chemicals, pesticides, petrochemicals, pharmaceuticals, and explosives. Workers involved in the production or use of o-Nitrotoluene may be exposed through the skin or from breathing it.
  • Riddelliine (not to be confused with Ritalin): Riddelliine is a botanical that is found in certain plants of the genus Senecio (a member of the daisy family). Senecio plants include ragwort and groundsel. In experimental animals, riddelliine has been linked with cancer of the blood vessels, leukemia, liver cancer, and lung tumors. Riddelliine-containing plants have no known commercial uses in the United States, but may be found in herbal medicines in other parts of the world.
  • Styrene: Used in the manufacture of products such as rubber, plastic, insulation, fiberglass, pipes, car parts, food containers, and carpet backing. Workers in certain occupations may have high levels of exposure. In the general population, the greatest exposure to styrene comes from cigarette smoking.

With these additions, the Report on Carcinogens now contains 240 listings. The likelihood of cancer following exposure to a known or possible carcinogen depends on many factors, including the amount of exposure, the duration of exposure, and a person’s underlying susceptibility to cancer.

Reference: NIH news. 10 June 2011: New substances added to HHS Report on Carcinogens.

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