Water Tainted with Chromium-6 in Desert Cities, Explained

Creative Commons photo by theducktest

According to a study of utility test results undertaken by the Coachella Valley newspaper the Desert Sun, tap water in Valley cities contains the known human carcinogen hexavalent chromium in concentrations that far exceed maximum levels proposed by the State of California.

Hexavalent chromium, also called Chromium-6, is a highly oxidized form of the metallic element in which the atoms are "missing" six electrons. Known to cause cancer if inhaled over long periods, the health effects of ingesting Chromium-6 in drinking water are less well established, but studies have suggested links to both lung and stomach cancers.

The proposed California drinking water standard is .02 micrograms of Chromium-6 per liter of drinking water, or .02 parts per billion (ppb). The federal limit on chromium in drinking water is 100 ppb, but Federal standards on chromium in drinking water do not distinguish among valences of the element -- thus combining any hexavalent chromium found with the more common Chromium-3, a less-oxidized, more benign form of the element that's actually a vital nutrient. California's overall limit on chromium in drinking water is 50 ppb.

The Desert Sun has not, at this writing, made its report available to readers for examination. However, in his story on the report, Desert Sun writer Keith Matheny said:

Chromium-6 is found at levels ranging from around 1 to 3 parts per billion in portions of the west valley, to more than 20 parts per billion in some east valley areas.

A quick survey of available water quality reports from the Coachella Valley's water agencies supports the Desert Sun's reports. The Mission Springs Water District, which provides water to Desert Hot Springs, Whitewater and adjacent portions of Palm Springs, reported finding hexavalent chromium at levels as high as 17 ppb in Desert Hot Springs' water in tests conducted in 2007. The Coachella Valley Water District, which serves the majority of the rest of the Valley outside of Palm Springs, reported an average of 8.4 ppb in the Rancho Mirage/Palm Desert area, 15 ppb in the Indio Hills/Sky Valley area, and 10 ppb in Thermal and Oasis. Those averages included highs of 18, 19 and 21 ppb, respectively.

Hexavalent chromium levels for drinking water in other cities is harder to find. The Desert Water Agency, which serves Palm Springs, doesn't list tests for hexavalent chromium in its water quality documents. The Indio Water Authority, which serves the city of Indio, lists only Chromium. The Coachella Water Authority, which serves the city limits of Coachella, doesn't offer water quality documents on its website.

Hexavalent chromium has been in the news in other Southern California cities as well. The EPA is ramping up investigation of Chromium-6 contamination of groundwater in Burbank and Glendale. Two weeks ago the utility Pacific Gas and Electric (PG&E) agreed to pay $3.6 million in fines for violating the Lahontan Water Board's order to clean up a plume of Chromium-6 in groundwater in the town of Hinkley -- the same locale whose Chromium-6 pollution made Erin Brockovich a household word. In Hinkley and the San Fernando Valley, industrial activity is responsible for the presence of Chromium-6 in the groundwater. The substance is used for corrosion-resistant coatings, as well as in the production of stainless steel and in other industrial pursuits.

In the Coachella Valley, however, the Chromium-6 seems to have gotten there without human assistance, deriving naturally from the serpentinitic rocks along the San Andreas Fault. These natural processes apparently suffice to provide Coachella Valley groundwater with Chromium-6 levels five times greater than those in Hinkley during the Brockovich case.

Those levels would also seem to be much greater than those listed in a much-publicized 2010 report on Chromium-6 by the Environmental Working Group (EWG). In its report, EWG tested Chromium-6 levels in tap water of 35 cities across the U.S. The most-contaminated water was found in Norman, Oklahoma, which had 12.9 ppb of Chromium-6 in its tap water. Honolulu, Riverside, Madison Wisconsin, and San Jose rounded out the top five, with levels ranging from 2 to 1.34 ppb -- far lower than the figures for desert cities.

Despite EPA assurances when EWG's report was released that the agency would ramp up research on the health issues involved with ingestion of Chromium-6, no results have yet been released. The National Toxicology Program of the National Institutes of Health has established that ingestion of compounds containing hexavalent chromium can cause cancers in laboratory animals, including mouth and intestinal cancers of kinds rarely seen otherwise. The applicability of these results to human health is still under debate.

To some extent this is due to the complex toxicology of Chromium-6, and the relative ease with which it transforms into the more benign Chromium-3 -- and vice versa. Contact with acidic substances can reduce -- or reverse the oxidation of -- Chromium-6 to Chromium-3. Naturally occurring Chromium-6 is more likely to be found where there's little organic matter in soils to acidify groundwater -- as is the case in the California deserts. Stomach acids can also reduce Chromium-6, as can additives such as orange juice, tea or coffee. Conversely, adding chlorine to water for public health purposes can oxidize Chromium-3 into Chromium-6. Tracking Chromium-6 through the body to track its damage to living cells is thus a difficult task.

And part of the debate is due -- some allege -- to persistent industry interference in the peer-review process. EWG, for instance, claims that a consulting company on retainer with PG&E during the Hinkley lawsuit purposely distorted Chinese scientists' findings that Chromium-6 ingestion was linked to stomach cancer, cooked the results to erase the link between illness and exposure, and published the resulting paper in the April 1997 issue of the Journal of Occupational and Environmental Medicine under the names of the Chinese research team:

The documents show that ChemRisk employees -- with the knowledge of PG&E's attorneys -- conducted their own analysis of Zhang and Li's data, deliberately ignoring statistics on cancer in the province that pointed to an association with chromium-6. They then wrote and submitted the article for publication without disclosing that they worked for ChemRisk or that PG&E had paid for the new "study." Zhang, now deceased, was a paid consultant to the project, but the documents suggest his biggest contribution was providing his original data. Nowhere in the published article are the names of the ChemRisk employees who worked on it, or any indication that the paper was part of PG&E's legal defense strategy.

The Journal of Occupational and and Environmental Medicine ended up retracting the paper, citing the submitters' lack of disclosure of their financial ties to PG&E.

Despite corporate interference, the scientific case for caution is mounting.The EPA's draft Toxicological Review of Chromium-6 states:

[H]exavalent chromium is "likely to be carcinogenic to humans" via the oral route of exposure based on a statistically significant increase in the incidence of tumors of the oral mucosa and tongue of rats and of the small intestine of mice; and evidence of an association between oral exposure to hexavalent chromium and stomach cancer in humans. Additionally, available evidence indicates that chromium interacts with DNA, resulting in DNA damage and mutagenesis. Thus, hexavalent chromium is proposed to induce carcinogenicity via a mutagenic mode of action.

The EPA is in the process of revising the assessment after peer review, and maintains that the draft should not be taken as formal policy of the agency. Among the public commenters during the peer review phase were representatives of water agencies, which would face the prospects of substantial expenses if regulators crack down on Chromium-6 in drinking water. It'll be interesting to see how the final version changes, and what effect those changes may have on an eventual Chromium-6 standard.

In the meantime, Coachella Valley residents have to figure out what, if anything, they can do to protect themselves from their polluted drinking water. Chromium in bottled water is not regulated, and rarely tested for. Filtering hexavalent chromium out of tapwater is possible, but generally requires reverse-osmosis filters that can cost hundreds of dollars to purchase and install. Some pitcher filtration systems claim to remove chromium, but require frequent filter changes that can run expenses out of reach of the Valley's poorest households -- which tend to be in those regions with the worst chromium contamination. Until regulators settle on hard limits to Chromium-6 and enforce them, many of us will just have hope for the best.

Chris Clarke is an environmental writer of two decades standing. Author of Walking With Zeke, he writes regularly at his acclaimed blog Coyote Crossing and comments on desert issues here every week. He lives in Palm Springs. Read his previous posts here.