Chromium-6 in Drinking Water:  MCL Update

Last Update: November 2, 2009

Chromium-6 is currently regulated under the 50-micrograms per liter (µg/L) maximum contaminant level (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.

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 Environmental Protection Agency (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.

In 1999, as part of the process of reviewing maximum contaminant levels (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 1999-2001and 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 Office of Environmental Health Hazard Assessment (OEHHA).  

In the absence of a PHG, CDPH cannot propose an MCL for chromium-6.

In August 2009, OEHHA released a draft PHG for chromium-6 of 0.06 µg/L .  

Once the chromium-6 PHG is final, CDPH can proceed with the MCL process.