Credit: Trevor MacInnis
The US Department of Health and Human Services (HHS) has identified 1 chemical substance as a known human carcinogen and 3 additional substances as likely carcinogens.
Ortho-toluidine, which is used to make rubber chemicals, pesticides, and dyes, has been shown to cause urinary bladder cancer and is now listed as a known human carcinogen.
The 3 substances that are likely to be human carcinogens are 1-bromopropane, cumene, and pentachlorophenol.
1-bromopropane is used as a cleaning solvent and spray adhesive. Cumene is used to make phenol and acetone, and it is found in fuel products and tobacco smoke. Pentachlorophenol is a mixture used to preserve wood.
Exposure to pentachlorophenol is associated with an increased risk of non-Hodgkin lymphoma in humans and solid tumor malignancies in mice. Cumene and 1-bromopropane have been linked to solid tumor malignancies in mice as well.
All 4 substances are listed in the HHS’s 13th Report on Carcinogens, a science-based document prepared by the National Toxicology Program (NTP) that identifies chemical, biological, and physical agents considered to be cancer hazards for people living in the US.
The new report has a total of 243 listings, which includes known carcinogens and substances “reasonably anticipated” to be carcinogens.
“Identifying substances in our environment that can make people vulnerable to cancer will help in prevention efforts,” said Linda Birnbaum, PhD, director of the National Institute of Environmental Health Sciences and the NTP.
“This report provides a valuable resource for health regulatory and research agencies, and it empowers the public with information people can use to reduce exposure to cancer-causing substances.”
New known carcinogen
Since 1983, ortho-toluidine has been listed in the HHS’s Report on Carcinogens as reasonably anticipated to be a human carcinogen. However, new cancer studies led the NTP to reevaluate and reclassify ortho-toluidine. It is now classified as a known human carcinogen, based on clinical studies showing it causes urinary bladder cancer.
Ortho-toluidine is a synthetic chemical produced in other countries and imported into the US by several companies in high volumes. It is primarily used to make rubber chemicals, pesticides, and dyes. It is also used in some consumer and medical products.
People are mainly exposed through the workplace, by skin contact and/or inhalation when using ortho-toluidine. They can also be exposed outside the workplace through sources such as tobacco smoke.
Three new substances likely to be carcinogenic
Pentachlorophenol
Pentachlorophenol and byproducts of its synthesis are complex mixtures of chemicals used as wood preservatives. Because virtually everyone exposed to pentachlorophenol is also exposed to its synthesis byproducts, they were evaluated together.
In the US, pentachlorophenol has been regulated since the 1980s as a restricted-use pesticide. It is used industrially for treating utility poles, wood pilings, fence posts, and lumber or timber for construction.
Most exposure has occurred in settings where workers treat lumber or come in contact with treated lumber. People may also be exposed to this mixture from breathing contaminated air or dust, or from contact with contaminated soil.
Exposure to this mixture was associated with an increased risk of non-Hodgkin lymphoma in clinical studies. In mice, it has been shown to cause tumors in the liver and other organs.
1-bromopropane
1-bromopropane is a liquid used as a solvent in many commercial industries. It is used as a cleaner for optics, electronics, and metals, as well as a solvent for aerosol-applied adhesives such as those used in foam cushion manufacturing.
It is also used in dry cleaning and in solvent sprays for aircraft maintenance. Workers in certain occupations may be more exposed to 1-bromopropane than the general population.
The NTP did not identify any clinical studies that evaluated the relationship between human cancer and exposure to 1-bromopropane. However, inhalation exposure to 1-bromopropane in rodents caused tumors in several organs, including the skin, lungs, and large intestine.
Cumene
Cumene is a flammable and volatile liquid with a gasoline-like odor. It is a natural component of coal tar and petroleum, and is found in tobacco smoke. It is used primarily to make acetone and phenol.
People are mainly exposed to cumene through the environment and in workplaces that use or produce cumene. It can be found in emissions from petroleum products.
Inhalation exposure to cumene caused lung tumors in male and female mice, and liver tumors in female mice. The NTP did not identify any clinical studies evaluating the relationship between cancer and exposure to cumene.
