Hexavalent chromium, the chemical made famous by the 2000 film "Erin Brockovich," is once again in the news after an environmental organization released a report indicating that the chemical has contaminated drinking water in more than 30 cities nationwide.
The Environmental Working Group tested tap water in 35 cities and found hexavalent chromium, or chromium-6, in 31 of the cities.
Chromium-6 was the same chemical that had seeped into the groundwater of Hinkley, Calif., where Erin Brockovich waged her fight, and whose residents were awarded a $333 million settlement from Pacific Gas and Electric Co. The movie drew attention to the potential dangers of hexavalent chromium, and scientists at the Environmental Working Group say previous research found the chemical can cause cancer, and that its presence in drinking water is much more widespread than originally believed.
But as the Environmental Working Group stresses the potential dangers of chromium-6, other scientists say there's no good science on just how much of an impact the chemical can have on public health.
"The National Toxicology Program has found that hexavalent chromium in drinking water shows clear evidence of carcinogenic activity in laboratory animals, increasing the risk of otherwise rare gastrointestinal tumors," reads the report's executive summary. The National Toxicology Program is a branch of the U.S. National Institutes of Health, and considers hexavalent chromium a "probable carcinogen."
"There have also been some other health effects seen in animal studies, such as anemia and damage to the lymph nodes, liver and gastrointestinal tract," said Rebecca Sutton, the report's lead researcher.
Sutton also said she was surprised by the number of cities that had contaminated water.
"I expected to find it in some cities, but had no indication I would find it in others," she said.
Regulations set by the Environmental Protection Agency set a total chromium limit of 100 ppb, or parts per billion, for drinking water. However, there is no set limit for chromium-6, and water utility companies are not required to test for it. California is the only state that mandates testing, and that state's legal limit for chromium-6 in drinking water is .06 ppb. Sutton and her colleagues found that 25 of the 31 cities with chromium-6 contaminated water had levels higher than that amount.
Norman, Okla., the city with the highest concentration of chromium-6, measured about 200 times that level, with a concentration of about 12 ppb.
But other scientists say that's an extremely small amount. One part per billion is equivalent to about a drop in 250 gallon drums of water, or three seconds in a century. Even if a city such as Norman has the highest concentration of chromium-6 of all the cities tested, that doesn't mean it places the residents at a higher risk for developing cancer than in other cities.
Dangers of Chromium-6 in Drinking Water Unknown
Toxicology experts say inhaling chromium-6 can cause cancer, but there isn't much data on the dangers of drinking it.
"The evidence is fairly good that it's carcinogenic in people in occupational settings who inhale it and get a good dose," said Dr. Shan Yin, assistant medical director of the Cincinnati Drug and Poison Information Center.
"No one has really established what is a carcinogenic level for drinking water," said Alfred Aleguas, managing director at the Northern Ohio Poison Control Center in Cleveland. "We need to establish what is a limit we have to be concerned about."
Aleguas also said that the levels of exposure in Hinkley were much higher -- 580 ppb -- than the 31 ppb the Environmental Working Group found in Norman, Okla., the city with the highest concentration of chromium-6 in the group's report.
Most unintentional chromium exposure comes from industrial processes, such as leather tanning and metal plating. It's also a naturally occurring substance.
Chromium-3 is a nontoxic form of chromium that is vital to the body's glucose metabolism. But while there's still debate over how much chromium-6 is too much, the EPA said in a statement that it's currently assessing the impact of chromium-6 on public health. The final scientific review will be available sometime next year, and the EPA will determine if a new level needs to be set.