Chromium-6 in Drinking Water: MCL Update
Last Update: April 15, 2014
Current MCL for Total Chromium
Chromium-6 (hexavalent chromium) is currently regulated under the 50-micrograms per liter (µg/L) primary drinking water standard (maximum contaminant level, MCL} for total chromium. California's MCL for total chromium was established in 1977, when we adopted what was then a "National Interim Drinking Water Standard" for chromium. The total chromium MCL was established to address exposures to chromium-6, the more toxic form of chromium. Chromium-3 (trivalent chromium) is a required nutrient.
The US Environmental Protection Agency (EPA) adopted the same 50-µg/L standard tor total chromium, but in 1991 raised the federal MCL to 100 µg/L. California did not follow US EPA's change and stayed with its 50-µg/L standard.
A Specific MCL for Chromium-6
In 1999, as part of the process of reviewing MCLs in response to public health goals (PHGs), CDPH's precursor, the California Department of Health Services (CDHS), identified the chromium MCL as one for review. In particular, we sought to determine whether or not an MCL that is specific for chromium-6 would be appropriate. Subsequently, events primarily between 1999-2001 and concerns about chromium-6's potential carcinogenicity when ingested resulted in a state law that requires CDPH to adopt a chromium-6-specific MCL (see chromium-6 timeline).
California's Health and Safety Code guides the development of an MCL for chromium-6: §116365.5 requires the adoption of an MCL for chromium-6 by January 1, 2004. In addition, Health and Safety Code §116365(a) requires CDPH to establish an MCL at a level as close as is technically and economically feasible to the contaminant's PHG, which is the concentration of a contaminant in drinking water that does not pose a significant risk to health. PHGs are developed by Cal/EPA's Office of Environmental Health Hazard Assessment (OEHHA).
In July 2011 OEHHA established a PHG for chromium-6 of 0.02 µg/L. The PHG represents a de minimis lifetime cancer risk from exposure to chromium-6 in drinking water, based on studies in laboratory animals. OEHHA has also prepared a PHG fact sheet.
The availability of the chromium-6 PHG enabled CDPH to proceed with setting a primary drinking water standard (see the MCL process).
As part of the rulemaking process, on August 23, 2013, CDPH proposed an MCL for chromium-6 of 0.010 milligram per liter (equivalent to 10 µg/L) and announced the availability of the proposed MCL for public comment (see the CDPH press release). The comment period closed on October 11, 2013.
The Office of Regulations' webpage includes the proposed regulations and other related materials and information.
Completion of the rulemaking process may take up to 12 months after the proposal. In the absence of any major delays, an enforceable MCL is anticipated to be established in 2014.
Information about chromium-6 in drinking water and its regulation is available in our Fact Sheet (PDF)
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Readers interested in the levels of chromium in their drinking water should refer to their water systems' annual Consumer Confidence Reports (CCRs). Many CCRs for California water systems are available on the US EPA's CCR website.