Officials stressed that the listings do not mean that any exposure to the substances will cause cancer. Instead, it means that the latest scientific evidence indicates that the agents can cause cancer in some people exposed to enough of the compounds under the right circumstances. Most of the evidence for a cancer risk came from people exposed to relatively high levels in industrial settings.
“A listing . . . does not by itself mean that a substance will cause cancer,” John Bucher, associate director of the National Toxicology Program, which issues the list, said during a briefing for reporters. “Many factors, including the amount and duration of exposure and an individual’s susceptibility to a substance, affect whether a person will develop cancer.”
The listings do not trigger any immediate new restrictions on the substances, but other government agencies may use the information in the future as part of their regulatory decisions, Bucher said. In the meantime, individuals can use the list to make personal choices, he said.
“We’re exposed to carcinogens every day all the time, from sunlight to alcoholic beverages,” Bucher said, noting that most people’s routine exposure to the newly listed substances was probably low. “The purpose is to give people information to allow them to make choices. You can avoid using products that might contain these materials if you think there will be a hazard.”
The listings were immediately denounced by industry groups, which has lobbied against the styrene and formaldehyde listings.
“Exposure to styrene does not cause cancer in humans,” a statement from the American Composites Manufacturers Association said. The association charged that the process used to evaluate the substance was flawed and that the report threatened thousands of jobs in industries that use the chemical.
The report is a congressionally mandated list prepared by the National Institute of Environmental Health Sciences, which is part of the National Institutes of Health.
With the additions in the 12th version of the report, 240 substances are now listed as either “known human carcinogen” or “reasonably anticipated to be a human carcinogen.”
Formaldehyde had been listed in the “reasonably anticipated” category since the second report, based on studies showing it caused nasal cancer in rats.
In addition to being used as a preservative in medical laboratories, formaldehyde is widely added to make resins for household items, such as composite wood products, plastics and coatings for paper products. It also is in some consumer products, such as hair-straighteners.
The substance was moved into the “known carcinogen” category based on additional research that found those with higher exposure were at increased risk for certain types of rare cancers, including cancer of the throat and a cancer of white blood cells known as myeloid leukemia, officials said.
Aristolochic acids, a family of compounds that occur naturally in some plants and are found in some herbal remedies, was also listed as a known carcinogen. The Food and Drug Administration in 2001 warned against using any products containing the acids, but they are still sold on the Internet and are found in herbal products used to treat a variety of conditions, including arthritis, gout and inflammation. The acids can cause bladder and urinary tract cancer in people with kidney or liver disease, the agency said.
Styrene was among six new substances “reasonably anticipated” to be carcinogenic. Styrene is a synthetic chemical used to make products such as rubber, plastic, insulation, pipes, car parts, food containers and carpet backing. It is found in cigarette smoke.
The average person can be exposed to styrene by indoor air containing vapors from building materials and other products. Workers can also be exposed in industrial settings. Low levels can also leach out of coffee cups and other food containers.
Studies involving people and animals indicate it can cause genetic damage to white blood cells.
Other additions to the list of substances ““reasonably anticipated” to be human carcinogens were:
l Captafol, which is a fungicide used to control fungal diseases in fruits, vegetables, plants and grasses. It has been banned in the United States since 1999, but past exposures may still affect people. It has been linked to various types of tumors.
l Cobalt-tungsten carbide, which is used to make cutting and grinding tools and other products used in many industries, including oil and gas drilling and mining.
l Inhalable glass wool fibers found in home and building insulation.
l O-Nitrotoluene, which is used to make dyes for fabrics, leather and paper as well as agricultural chemicals, rubber chemicals, pesticides and explosives.
l Riddelliine, which is also found in some herbal medicines, including teas. It has been found to cause cancer of the blood vessels in rats and mice, leukemia and liver cancer in rats and lung tumors in mice.