Chromium-6 in Drinking Water: MCL Update
Last Update: July 9, 2012
Current MCL for Total Chromium
Chromium-6 is currently regulated under the 50-micrograms per liter (µg/L) 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, which is considered to be the more toxic form of chromium. The US EPA adopted the same standard, but in 1991 raised the federal MCL to 100 µg/L. California did not follow US EPA's lead and stayed with its 50-µg/L MCL for total chromium.
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.
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. [PHGs are contaminant concentrations in drinking water that do not pose a significant risk to health. PHGs are developed by Cal/EPA's OEHHA].
On July 27, 2011, OEHHA established its PHG for chromium-6 at a concentration 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, as presented in OEHHA's technical support document. OEHHA has also prepared a PHG fact sheet.
The availability of a final PHG enables CDPH to proceed with setting a primary drinking water standard (see the MCL process). Based on past experience, CDPH estimates the MCL development process will take approximately 18-24 months and is working to have an MCL developed and available for public comment by July 2013. The rulemaking process may then take an additional 12-24 months. Assuming the process moves along without any major delays, an enforceable MCL would be established between July 2014 and July 2015.
Additional information is available from CDPH's chromium-6 fact sheet (PDF).