RoC Review of Antimony Trioxide

Q: If I am exposed to antimony trioxide, will I get cancer?
A: U.S. residents should take steps to reduce exposure to antimony trioxide to decrease cancer risk. A listing in the RoC identifies a substance or exposure circumstance as known or reasonably anticipated to be a human carcinogen and thus indicates that it can cause cancer under certain circumstances. Many factors affect whether a person will or will not develop cancer, including the carcinogenic potency of the substance, the level and duration of exposure, and an individual’s susceptibility to the carcinogenic action of the substance.

Q: How could a person be exposed to antimony trioxide?
A: Scientists can infer antimony trioxide exposure by testing blood and urine. Exposure can occur through multiple ways. People who work in industries that use antimony trioxide may have higher levels of exposure than the U.S. population at large.

The most common exposure is through inhaling air contaminated with antimony trioxide, for which likelihood is greatly increased in workplaces that use or process antimony trioxide. Indoor air might contain fine dust from the wear and tear of flame-retardant-treated products containing antimony trioxide.

Exposure can also occur from converting other forms of antimony to antimony trioxide, such as through burning coal and petroleum, incinerating waste containing antimony, or abrasion from vehicle brake pads made with antimony. Chemical and transportation workers or residents who live near plants using antimony are more likely affected. Exposure can also happen through skin contact, which typically only concerns certain workers.

Q: Is there guidance or regulation for people who work in industries that use antimony trioxide?

A: Decreasing or eliminating workplace exposure is the main prevention method. Several agencies, such as the Environmental Protection Agency, the Department of Transportation, the Occupational Safety and Health Administration, the National Institute for Occupational Safety and Health, and American Conference of Governmental Industrial Hygienists have regulations and guidelines to limit exposure to antimony trioxide in the workplace and the environment. The European Union Risk Assessment Report also contains information on antimony trioxide, which is also known as diantimony trioxide.

Q: Why is reviewing antimony trioxide important for public health?
A: NTP selected antimony trioxide for review for the RoC based on potential for widespread occupational exposure and an adequate database of cancer studies in experimental animals, including the recently completed NTP inhalation studies of antimony trioxide in mice and rats. Workers at more than 273 companies in the U.S. have potential to be exposed to antimony trioxide. People in their everyday lives may also be exposed to low levels of antimony trioxide.

NTP received two nominations to study the potential carcinogenicity of antimony trioxide. The U.S. Consumer Product Safety Commission nominated it for carcinogenicity testing in experimental animals based on concerns for workers and consumer products. Based on concerns for occupational exposure, the National Institute for Occupational Safety and Health nominated antimony trioxide for review for the RoC.

Q: What studies did NTP use to determine antimony trioxide’s listing status?
A: NTP used three types of studies: animal, mechanistic, and human. The RoC evaluation considered the carcinogenicity testing results from the Division of the National Toxicology Program at NIEHS as well as other studies. In experimental animals, inhalation exposure to antimony trioxide caused lung tumors in rats and mice of both sexes, adrenal gland tumors in female rats, skin tumors in male mice, and tumors of the lymphatic system in female mice. These data fulfill the listing criteria for reasonably anticipated as a human carcinogen.

The data available from studies in humans were inadequate to evaluate the relationship between human cancer and exposure specifically to antimony trioxide. In cultured cells, whole animals, and humans, antimony trioxide induced several biological effects that are characteristics of carcinogens and provided supporting evidence to antimony carcinogenicity.

Q: How are conclusions drawn?
A: Substances are listed in the RoC as known or reasonably anticipated to be a carcinogen using established listing criteria. Conclusions are based on scientific judgment, using systematic review methods, with consideration given to all relevant information.

For a substance to have the status of known to be a human carcinogen, there must be sufficient evidence of carcinogenicity from studies in humans, showing a cause-and-effect relationship between exposure to the substance and human cancer. Occasionally, substances are listed in this category based on human studies showing that the substance causes biological effects known to lead to the development of cancer.

For a substance to have the status of reasonably anticipated to be a human carcinogen, at least one of the following three situations must occur:

• Limited evidence of carcinogenicity from studies in humans, which indicates that causal interpretation is credible but that alternative explanations, such as chance, bias, or confounding factors, could not adequately be excluded. 
• Sufficient evidence in experimental animals showing a cause-and-effect relationship between exposure to the substance and cancer. 
• Member of a class of substances already listed in the RoC, or the substance acts through mechanisms indicating it would likely cause cancer in humans.

Q: What were the results of the peer review of antimony trioxide?
A: On August 12, 2014, a panel of experts reviewed the Draft Report on Carcinogens Monograph on Antimony Trioxide and unanimously agreed with NTP’s recommended listing, reasonably anticipated to be a human carcinogen. The panel included experts in public health, toxicology, pathology, and other fields.