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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 Published: December 26, 2010

But Sutton, Nairn and Norman Utilities Director Ken Komiske all said chromium in the Norman area most likely occurs naturally because of heavy metal content in the area's groundwater.

Nairn said Norman's level of chromium 6 struck him as “pretty low, and we've got naturally occurring concentrations in our groundwater.”

Reason for concern

Scientists are not sure how much chromium 6 ingested orally constitutes a cancer risk.

California legislators and health officials wanted to find out, so they asked the National Toxicology Program, headquartered at the National Institute of Environmental Health Sciences to conduct tests on the toxicity of chromium 6 in drinking water.

A compound that contained extremely high levels chromium 6, ranging from five to 180 milligrams per liter, was given to mice and rats over a two-year period. The rats had malignant tumors in their mouths while the mice had benign and malignant tumors in their small intestines that increased according to the dose they received.

Meanwhile, the EPA is assessing the risk of chromium 6 and will determine what new standards may be required.

Some states already have lowered the total chromium limit of 50 parts per billion for their water systems; and a proposal in California calls for limiting chromium 6 to 0.06 parts per billion.

Most cities in Monday's report had levels that exceed the proposed California limit, but that may not be an automatic cause for concern.

“The report I saw compared everything to a number that's not approved by the EPA and is not fully vetted,” said David Sabatini, an OU civil engineering professor and director of Water Technologies for Emerging Regions (WaTER).

“They're failing to point out that (Norman) is much lower than the EPA standard,” Sabatini said, “and just comparing the 12 to 0.06 creates a panic.”

Sabatini and Nairn both brought up the EPA's science-based decision to lower the acceptable levels of arsenic, which forced Norman to close wells to meet compliance. They said the same could happen someday with chromium 6.

“There's good data that it is carcinogenic, but what the ‘quote unquote' safe level is still being explored; that's the big debate,” Nairn said.