|Hexavalent Chromium in Drinking Water Causes
Cancer in Lab Animals
Researchers announced today 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
“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,
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.