An expert panel, which met Jan. 24 via webcast, was unanimous in agreeing with National Toxicology Program (NTP) scientists that antimony trioxide should be classified as reasonably anticipated to be a human carcinogen in the Report on Carcinogens (RoC). Antimony trioxide is a compound used in the production of certain flame retardants and other industrial processes.
NTP presented a draft report that is known as a monograph, because it focuses on a specific subject. The monograph includes the NTP conclusion and the relevant research on which it is was based. Summarized studies included those in experimental animals and mechanistic information related to carcinogenicity.
Rebecca Fry, Ph.D., from the University of North Carolina at Chapel Hill (UNC), chaired the peer review meeting.
The panel agreed unanimously that studies in experimental animals, including 2-year NTP inhalation studies, provided sufficient evidence of carcinogenicity. The experts reviewed the experimental animal studies, human cancer studies, mechanistic studies, and the overall evaluation of the substance.
Panel member Richard Peterson, D.V.M., Ph.D., from AbbVie, commented on the overall evaluation. “It is well-written, integrated, and sums up the monograph well,” he said.
“This has been a very thorough review,” said NTP Senior Scientist John Bucher, Ph.D. Noting that peer review is a crucial part of the NTP listing process, Bucher thanked the panel for their attention to detail.
NTP selected antimony trioxide for review for the RoC for two reasons — the potential for substantial human exposure in workplaces, and an adequate database of cancer studies in experimental animals.
Antimony trioxide is primarily used as a chemical agent in halogenated flame retardants for canvas and textiles, so it is present in some furniture, draperies, and carpets. The substance is also used in the production of polyethylene terephthalate plastic, enamel and paint pigments, ceramics, and optical and art glass.
Occupational exposure via inhalation is the major concern, due to widespread use in industrial processes. NTP cited data that suggests 273 companies in the United States may process or use flame retardants that contain antimony trioxide.
The general population may be exposed through the wear and tear of consumer products treated with flame retardants, such as textiles, carpets, and upholstered furniture. Additional exposures occur through air emissions from facilities using antimony trioxide and from automobile braking. Antimony trioxide is produced when brake pads and brake lubricants that contain antimony are oxidized.
NTP will revise the monograph based upon consideration of comments received. The peer review outcome will be shared with the NTP Board of Scientific Counselors at its June meeting.
(Ernie Hood is a contract writer for the NIEHS Office of Communications and Public Liaison.)