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Chromium-6 Drinking Water MCL


MCL for Hexavalent Chromium

The 0.010-milligram per liter MCL for hexavalent chromium (also referred to as chromium-6), equivalent to 10 micrograms per liter (µg/L), became effective on July 1, 2014. The regulations are included in Drinking Water-Related Regulations, in the Drinking Water Law Book.


In 1999, as part of the process of reviewing MCLs in response to public health goals (PHGs), The California Department of Public Health's (CDPH's) precursor, the California Department of Health Services (CDHS), identified the total chromium MCL (see below) as one for review. (CDPH’s Drinking Water Program is now the State Water Board’s Division of Drinking Water.)

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) required 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 also prepared a PHG fact sheet. The availability of the chromium-6 PHG enabled CDPH to proceed with setting a primary drinking water standard.

As part of the rulemaking process, in August 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. The public comment period closed in October 2013. CDPH reviewed the comments submitted by interested parties and responded to them in the final statement of reasons, which is part of the final hexavalent MCL regulations package. The CDPH Office of Regulations' webpage includes the regulations, the initial statement of reasons, the final statement of reasons, and other information.

On April 15, 2014, CDPH submitted the hexavalent chromium MCL regulations package to the Office of Administrative Law (OAL) for its review for compliance with the Administrative Procedure Act. On May 28, OAL approved the regulations, which were effective on July 1, 2014.

Readers interested in the levels of hexavalent 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.

MCL for Total Chromium

Chromium-6 has been regulated under the 50-µg/L primary drinking water standard (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.


(Updated 3/23/16)