Safety questions remain on chromium 6

Lab studies show extreme amounts of the metallic element caused cancer in mice and rats, but how much does it take to be harmful to humans?
BY JAMES S. TYREE jtyree@opubco.com Published: December 26, 2010
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— University of Oklahoma associate professor Robert Nairn, an expert on water quality, became popular among friends and colleagues when a report came out Monday that questioned the safety of Norman's water.


“I got a lot of e-mails from people wondering what's going on,” said Nairn, who directs OU's Center for Restoration of Ecosystems and Watersheds.

The concern is about hexavalent chromium, often called chromium 6. Norman had a chromium 6 reading of 12.9 parts per billion, which was highest among one-time samplings from 35 cities tested for a project commissioned by the Environmental Working Group.

Chromium 6 was proved decades ago to cause cancer or respiratory ailments when inhaled, and animal tests conducted in recent years by the National Toxicology Program show evidence that it also can be carcinogenic when ingested orally.

While Norman easily topped the new report's list of cities, the level was thousands times less than that given to lab animals that developed cancer.

It pales when compared to Hinkley, Calif., the city on which the movie “Erin Brockovich” was based, which had up to 580 parts per billion in its drinking water in the 1990s.

In spring 2009, Nairn was involved in the cleaning of shallow groundwater for Tinker Air Force Base, where he said the chemical's content ranged from 5,800 to 7,900 parts per billion.

“I think (the report) opened some eyes and said we should keep our eyes open for chrome 6,” Nairn said. “But I don't have a feel for chrome 6. What I can say is 6,000 (parts per billion) is something to worry about; 500 is something to worry about. But 12.9, I don't know. We don't know.”

Below the limit

What is known is that total chromium in Norman's ground wells consistently has tested below the federal and state limit of 100 parts per billion. Total chromium combines chromium 6 and the nutrient chromium 3.

According to a Norman Utilities Department statement, the most recent tests for total chromium had results ranging from 11 to 86 parts per billion in its ground water wells, while samples from the water treatment plant had levels that were not detectable.

Rebecca Sutton, an environmental chemist who worked on the Environmental Working Group study, said chromium 6 often is discharged by steel and pulp mills, and by metal plating and leather tanning facilities.

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