Chromium 6

Chromium-6 Final MCL

The California Department of Public Health (CDPH) has finalized the nation’s first drinking water standard for chromium-6. The standard – known as the maximum contaminant level, or MCL – is 10 parts per billion (ppb).

The MCL has been finalized by CDPH but will take effect only after it has been reviewed and approved by the Office of Administrative law in compliance with the Administrative Procedures Act. This review can take up to 30 working days to complete. Once approved, the regulation is then filed with the Secretary of State and will become effective the first day of the following quarter.

Once effective, the MCL will be an enforceable regulatory standard for chromium-6 in California drinking water.

In August 2013, CDPH published the nation's first draft maximum contaminant level (MCL) for hexavalent chromium, or chromium-6, proposing a standard of 10 parts per billion. ACWA remains actively engaged on this issue and is pleased to provide the following resources for use by our member agencies in communciating with the public about this proposed new standard. If you have questions about the content on this site, please contact Adam Walukiewicz, ACWA regulatory advocate, at or call 916-441-4545.  


Chromium is an inorganic chemical that is used in many industrial processes including electroplating, wood treatment, pigments manufacture and cooling tower treatment for corrosion control. However, chromium is also a naturally occurring element. In fact, chromium is the 11th most common element in the earth's crust.

Since the 1970s, California has enforced a drinking water standard for total chromium, which includes chromium-3 and chromium-6. That standard of 50 ppb is more stringent than the federal standard for total chromium of 100 ppb.

Recent California Developments

California's Office of Environmental Health Hazard Assessment (OEHHA) in July 2011 published a final chromium-6 public health goal (PHG) of 0.02 parts per billion (20 parts per trillion). At this level, it is estimated that not more than one person in 1 million who consumes a half-gallon of water daily for 70 years would be expected to develop cancer as a result of exposure.

A PHG is not an enforceable standard. State law requires the California Department of Public Health (CDPH) to use a PHG as guidance in developing a maximum contaminant level (MCL), which is the enforceable state standard for drinking water that public water systems must meet. CDPH used the PHG as a starting point and has been working for the past two years on the many technical and cost issues associated with chromium-6 treatment.

Background on OEHHA’s chromium 6 public health goal is available here.

On August 22, 2013, CDPH released a draft MCL for chromium-6 of 10 pbb. To get the latest information on the status of CDPH’s efforts including a timeline for the PHG and MCL development, visit the Department’s chromium-6 website.  

Communications Toolkit

ACWA has prepared updated talking points and FAQs for member agencies to use when discussing the final MCL. The tools are available here. (NOTE: Member log-in required to access tools. Don't have a log-in? Get one here.)

Recent Federal Developments

The U.S. Environmental Protection Agency is currently reviewing the current standards for total chromium and chromium-6.

EPA reviewed total chromium as part of the second six-year review that was announced in March 2010. The Agency noted in March 2010 that it had initiated a reassessment of the health risks associated with chromium exposure and that the Agency did not believe it was appropriate to revise the national primary drinking water regulation while that effort was in process.

In 2008, EPA began a rigorous and comprehensive review of chromium-6 health effects through its Integrated Risk Information System (IRIS) based on new science. When this human health assessment is finalized EPA will carefully review the conclusions and consider all relevant information to determine if the current chromium standard should be revised. See below for an update on those efforts on the health effects research.

In 2011, EPA asked water agencies to enhance their chromium monitoring through additional sampling and analysis specifically for chromium-6. EPA provided recommendations to water agencies through a memo available here. In addition, total chromium and chromium-6 were included in EPA’s third Unregulated Contaminant Monitoring Rule. EPA has asked water agencies to report detections of total chromium above 0.2 µg/L (parts per billion or ppb) and chromium-6 above 0.03 ppb between 2013 and 2015.

This process will add significant amounts of occurrence data that can be used by EPA and California to inform future efforts regarding the regulation of chromium-6 in drinking water.

To learn more about EPA’s chromium-6 activities, please visit EPA’s website.

Chromium-6 Health Effects

The effects of chromium-6 when it is ingested have been the subject of much debate.  It is a known fact that when some forms of chromium-6 are inhaled, they can cause cancer. However, experts have disagreed on its toxicity in drinking water due in part to the possible changes to chromium-6 in the stomach when it is ingested.

The following is some information and resources about past and current research on chromium-6 health effects:

  • EPA currently regulates total chromium based on noncancerous effects of the chemical such as its ability to cause liver damage, harm the kidney, damage nerve tissues, and cause skin irritations. 
  • The National Toxicology Program (NTP) announced in 2007 the results of a study that found chromium-6 caused oral cavity and small intestine cancers in laboratory animals when administered orally. The lowest doses given to the animals in the study were ten times higher than what humans could consume from the most highly contaminated water sources identified in California.  NTP's study resulted from a 2001 petition from California Office of Environmental Health Hazard Assessment (OEHHA) and CDPH. The NTP study results can be accessed at:
  • The Office of Environmental Health Hazard Assessment (OEHHA) relied on the NTP study results when they published their public health goal in 2011.
  • Over the past year, ToxStrategies has released the results of  its research on the toxicity of chromium-6 and its “mode of action” (how it causes cancer in the body). The research was also designed to provide information on the differences between rodents and humans with regard to internal dose and develop the models and data needed to do a state-of-the-art risk assessment using NTP’s 2007 findings. ToxStrategies’ research found that its risk assessment using new mode of action (MOA) study data supports the current MCL (100 ppb) as protective for sensitive human subpopulations. More information is available here:
  • EPA is working on a toxicological review specific to orally ingested chromium-6 through its Integrated Risk Information System (IRIS). Based on the recommendations of an external peer review panel that met in 2011 to review the draft assessment, EPA will consider the results of the ToxStrategies studies before finalizing its assessment. This new draft toxicity assessment will be combined with the inhalation assessment, which is also in draft development. 

Treatment Options

The federal and state approved technologies for removing total chromium from drinking water include coagulation/filtration, anion exchange, reverse osmosis, and lime softening. 

Because of research completed over the past decade by multiple water agencies and the state of California, three chromium-6 technologies have emerged as leading candidates with respect to feasibility and cost. Those are weak base anion exchange (WBA), strong base anion exchange (SBA), and reduction with ferrous iron/coagulation/filtration (RCF). 

In 2002, the City of Glendale embarked upon a four-phase research campaign to identify and install the most effective treatment technologies for removing chromium-6 from drinking water supplies. Funding for various parts of the research was provided by the U.S. EPA, Cities of Los Angeles, Burbank, and San Fernando, along with the Water Research Foundation, ACWA and the state of California through Proposition 50. To review Glendale Water and Power’s final report, please click here. Other water agencies in both northern and southern California continue to look at health-protective and cost-effective options for chromium-6 treatment.

Occurrence of Chromium-6 in California Water Supplies

CDPH worked with water systems in 2001-2002 to collect occurrence data for chromium-6 in California’s drinking water.  This sampling was mandatory for most systems since CDPH placed chromium-6 on the UCMR list in January 2001.

A map is available here with the locations of active community water system wells that had two or more detections above the DLR of 1 ppb between 2002-2010. DLR refers to detection limit for the purposes of reporting. The map defines "active community water systems" and does not include private wells, very small systems or water sources such as schoolsm which are considered non-transient, non-community water systems.

The availability of this data, along with the data from EPA’s UCMR3, will inform efforts to continue developing effective treatment options for the removal of chromium-6 in water sources throughout the state.

Comment Letters Needed on Draft Chromium-6 MCL

ACWA is encouraging its member agencies to prepare and submit comment letters to CDPH to help demonstrate the impact of the MCL on public water systems. To help facilitate that process, ACWA sent an alert to members on Sept. 18 with several suggested steps and resources.

View the alert here (member log-in required)

Map from AB 2222 report-detections above DLR.pdf579.46 KB
ACWA Comment Letter on Cr(VI) MCL (DPH-11-005).pdf5.34 MB