A recent report from the Environmental Working Group revealed the presence of hexavalent chromium in the tap water of 31 of 35 cities. Norman, Okla., had the highest level of all the cities tested. Water Quality Products (WQP) spoke with Dr. Robert Nairn of the University of Oklahoma (OU) to learn more about chromium-6.
Rebecca Wilhelm: What is chromium-6?
Robert Nairn: Chromium-6 is one form of the element chromium. In water, depending on pH and oxidation conditions, dissolved chromium may be present as the trivalent cation (Cr+3) or as hexavalent anions, in which chromium has an oxidation state of Cr+6.
Cr+3 is an essential micronutrient and is sometimes added to vitamins as a supplement. Cr+6 is currently being evaluated for its possible human carcinogenicity via ingestion (it is a known inhalation hazard).
Wilhelm: While Norman’s level of chromium-6 tops the list, is this amount really dangerous?
Nairn: The reported results are apparently for a single water sample (collected from a single random tap
on a single date) and although measurable concentrations were found, a thorough sampling and analysis program would be required to draw defensible conclusions.
Also, at this time, federal and state drinking water quality standards for chromium-6 do not exist.
Total chromium is regulated, and analyses of Norman’s water supply show it to be well below the
regulated concentration.
Although chromium-6 has been determined to be an inhalation hazard in occupational settings (and is regulated as such), its carcinogenic level in drinking water has not been definitively determined.
However, the U.S. Environmental Protection Agency (EPA) did issue guidance for enhanced monitoring of chromium-6 in drinking water on Jan. 11, 2011.
Wilhelm: Is there any way to tell if the chromium-6 detected occurs naturally or is present due to manmade causes?
Nairn: Chromium-6 may be present due to both natural processes (e.g., erosion) and anthropogenic activities (e.g., industrial processes).
Determination of source would depend on site-specific conditions.In most cases, chromium-6 levels in natural waters unaffected by pollution are quite low.
Wilhelm: Are most water supplies currently tested for chromium-6, or just total chromium? Is there a way to separate these?
Nairn: At this time, concentrations of total chromium are regulated and are therefore typically determined.
Because chromium-6 is not regulated, it is typically not included in a common suite of analyses designed to meet regulatory needs.
Measurement of chromium-6 and total chromium are both possible, although via different analytical techniques.
Wilhelm: Is there a way for the public to test their water at home for chromium-6?
Nairn: Because of the analyses required, it would be most appropriate to contract with a private laboratory for chromium-6 analysis.
Wilhelm: Do you expect the EPA to set a new, stricter regulation for chromium? If so, when do you predict that would happen?
Nairn: The U.S. EPA already regulates total chromium under the Safe Drinking Water Act and, prior to the recent report, had already begun a review of the health effects of chromium-6 in drinking water, which was released in draft form in September 2010. A final determination of whether to modify or add regulations is scheduled for 2011.
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