Chromium-6 in Drinking Water
Chris Wiant, M.P.H., Ph.D.

The Environmental Working Group (EWG) recently raised alarm over the presence of chromium-6 in single samples of drinking water from 31 of 35 U.S. cities tested.  The group’s report notes the average level of chromium-6 in the 35 samples (0.18 parts per billion, or “ppb”) is higher than the 2009 draft California health goal of 0.06 ppb, which was reissued in December 2010 with a revised goal of 0.02 ppb, for another round of public comment.

Environmental Protection Agency (EPA) Administrator, Lisa Jackson stated that all US drinking water systems are required to test for and meet the national drinking water limit of 100 ppb for total chromium.  At the moment, EPA does not require testing to distinguish what percentage of the total chromium is chromium-6 versus other forms such as chromium-3, so EPA’s total chromium standard assumes that the sample is 100 percent chromium-6. This means the current chromium-6 standard has been as protective and precautionary as the science of the time of its setting allowed. EPA notes that it is difficult to test drinking water for the two forms of chromium separately.  On January 11, 2011, EPA released guidance materials and recommended drinking water systems continue testing for total chromium and start testing for chromium-6.

Chromium is a naturally-occurring element in rocks, animals, plants, soil, and volcanic dust and gases that occurs in water in two chemical states:  chromium-3 (trivalent chromium) and chromium-6 (hexavalent chromium).  According to an EPA website, chromium-3 is “an essential element in humans.” Chromium-6 is of greater health concern.  Inhaling chromium-6 is a known cancer risk in occupational settings such as leather tanning and metal plating facilities.  Risks from ingesting chromium-6 in drinking water, however, are much less certain.  Research conducted in 2003, for example, found that chromium-6 ingested with drinking water at levels below 2000 ppb is rapidly converted to chromium-3 in the human stomach and that even trace amounts of chromium-6 are not systemically circulated.

A December 21, 2010 EPA News Release notes that based on new science on chromium-6, the Agency is “undertaking a rigorous and comprehensive review” of its health effects:  “In September, we released a draft of that scientific review for public comment. When this human health assessment is finalized in 2011, EPA will carefully review the conclusions and consider all relevant information, including the Environmental Working Group’s study, to determine if a new standard needs to be set.”  Ongoing research that investigates the way chromium-6 in drinking water moves through the body and the processes and levels that ingested chromium cause tumors will provide valuable (currently missing) data about chromium-6 at drinking water levels.  These new data at current drinking water levels can inform EPA’s risk assessment.  According to EPA,  it plans to complete the final risk assessment on chromium-6 in 2011.  Once the chromium-6 risk assessment is finalized, EPA says it will work quickly to determine if new standards are needed. According to an Agency Fact Sheet, EPA is proposing to classify chromium-6 as ‘likely to cause cancer’ in humans when ingested over a lifetime.

Addressing the chromium-6 issue, EPA Administrator, Lisa Jackson has said, “It is clear that the first step is to understand the prevalence of this problem….While the EWG study was informative, it only provided a snapshot in time. EPA will work with local and state officials to get a better picture of exactly how widespread this problem is.”

As with all drinking water contaminants it is important to balance the risk the chemical presents with the potential for human exposure and the availability of technology and policy solutions to manage the risk.  The Federal Safe Drinking Water Act guidance that EPA has used successfully to regulate other drinking water contaminants provides the basis for developing a standard for chromium-6 that will also protect human health.

EPA guidance materials for hexavalent chromium, January 11, 2011 available at:  http://www.epa.gov/aging/press/epanews/2011/2011_0111_1.htm

(Chris Wiant, M.P.H., Ph.D., is president and CEO of the Caring for Colorado Foundation. He is also chair of the Water Quality & Health Council.)

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