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BookmarkScienceDaily (May 17, 2007) — Researchers announced recently that there is strong evidence a chemical referred to as hexavalent chromium, or chromium 6, causes cancer in laboratory animals when it is consumed in drinking water. The two-year study conducted by the National Toxicology Program (NTP) shows that animals given hexavalent chromium developed malignant tumors.
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"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.
