"Previous studies have shown that hexavalent chromium causes lung cancer in humans in certain occupational settings as a result of inhalation exposure," said Michelle Hooth, Ph.D., NTP study scientist for the technical report. "We now know that it can also cause cancer in animals when administered orally."

The study findings were announced at the National Institute of Environmental Health Sciences (NIEHS) after the NTP Board of Scientific Counselors Technical Reports Review Subcommittee completed its independent peer review of the sodium dichromate dihydrate research report. Sodium dichromate dihydrate is an inorganic compound containing hexavalent chromium that was used in the NTP studies. The NTP is located at the NIEHS, part of the National Institutes of Health.

Hexavalent chromium compounds are often used in electroplating, leather tanning, and textile manufacturing and have been found in some drinking water sources.

Male and female rats and mice were given four different doses of sodium dichromate dihydrate in their drinking water ranging from 14.3 mg/l to 516 mg/l for two years.

The lowest doses given to the animals in the study were ten times higher than what humans could consume from the most highly contaminated water sources identified in California.

The researchers report finding significant increases in tumors at sites where tumors are rarely seen in laboratory animals. Male and female rats had malignant tumors in the oral cavity. The studies conducted in mice found increases in the number of benign and malignant tumors in the small intestine, which increased with dose in both males and females.

"We found that hexavalent chromium is absorbed from the gastrointestinal tract," said Hooth. "After it is orally administered, it is taken up by the cells in many tissues and organs."

Hexavalent chromium has been brought to the public's attention in many ways, most notably in the movie "Erin Brockovich." Eleven members from the California Congressional Delegation sent a letter to the NTP Director requesting the NTP conduct the studies. Nominations for studying this compound also came from the California Environmental Protection Agency and the California Department of Health Services. The NTP began work on this compound after gaining input from the public and a panel of scientific experts about the study design.

The two-year study is one of several studies that NTP has completed on this chemical. A series of three-month toxicity tests in rats and different mouse strains was published in January 2007 in the "NTP Toxicity Report Series" at http://ntp.niehs.nih.gov/go/29184.

Details about the meeting, subcommittee roster and draft technical reports are available at http://ntp.niehs.nih.gov/go/15833.

The National Toxicology Program is an interagency program coordinated by the U.S. Department of Health and Human Services. It is located at the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park. For more information about the NTP, visit http://ntp.niehs.nih.gov.

The National Institute of Environmental Health Sciences (NIEHS), a component of the National Institutes of Health, supports research to understand the effects of the environment on human health. For more information on environmental health topics, visit http://www.niehs.nih.gov/home.htm.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.