California is the first state to consider a limit on the “Erin Brockovich” chemical, which has been found in 31 of 35 U.S. cities recently surveyed.

Photo © Heather Rousseau / Circle of Blue Many U.S. cities have higher levels of hexavalent chromium, a carcinogen, in their drinking water than is recommended. Click image to enlarge.

The tap water in many U.S. metropolitan areas was found to have higher-than-recommended levels of chromium-6, a known carcinogenic compound that is not regulated by any state or national agency, according to a study released this week by a public health research and lobbying organization.

The Environmental Working Group (EWG) estimated that 74 million Americans in 42 states drink chromium-polluted tap water, much of which is likely the cancer-causing chromium-6 form.

Chromium-6 comes from industrial processes used to manufacture pigments, dyes and chrome plating, in addition to commonly being discharged from steel and pulp mills. It is also used to tan leather and prevent corrosion.

The compound, also known as hexavalent chromium, is best known from the 2000 biographical film Erin Brockovich, starring Julia Roberts.

Brockovich helped to wage a class-action lawsuit against Pacific Gas & Electric Company for contaminating groundwater in Hinkley, California. The company had hired consultants to produce sham research to obscure the link between the chromium-6 and elevated cancer rates, but, in the end, the residents of Hinkley—where chromium-6 concentrations reached as high as 580 parts per billion (ppb), with natural background levels of 1.19 to 3.09 ppb—were awarded a $333 million settlement in 1996.

Image courtesy EWG EWG commissioned testing for chromium-6 in tap water from 35 U.S. cities. Red dots indicate EWG’s test sites and measured hexavalent chromium concentrations in parts per billion (ppb). Size of dot reflects the level found. Brown-shaded areas represent population-adjusted average concentrations of total chromium by county, calculated from EWG’s national tap water database.

More recently, EWG commissioned laboratory tests of tap water from 35 U.S. cities, where previous testing by local utilities had shown high levels of “total chromium,” a measure that includes chromium-3, an essential nutrient for human glucose metabolism.

The average chromium-6 level of all 35 cities was 0.18 ppb, with samples from the city of Norman, Oklahoma registering the highest at 12.9 ppb. One part per billion is the equivalent of one faucet drip of pollutant in 66,000 gallons. Tests detected chromium-6 in samples from 31 cities, and 25 cities showed the toxic metal at concentrations above a 0.06 ppb limit being considered by regulators in California — the only state to require chromium testing.

The compound was undetected in:

Indianapolis, Indiana

San Antonio, Texas

Plano, Texas

Reno, Nevada

Image courtesy EWG EWG commissioned testing for chromium-6 in tap water from 35 U.S. cities. Tests detected chromium-6 in samples from 31 cities, and 25 cities showed the toxic metal at concentrations above the safe maximum limit, shown in red, that has been proposed by California regulators.

The U.S. Environmental Protection Agency does not regulate chromium-6 specifically, although it has set a total chromium threshold of 100 ppb to protect against skin irritation. EWG argues that it does not make sense to consider a toxic compound together with a beneficial nutrient, specifically chromium-3.

As a step toward a national chromium-6 standard, the EPA released a draft assessment of the compound in September of this year, presenting evidence linking over-exposure to higher cancer rates in humans. The EPA will determine if a new level needs to be set after a final review sometime next year.

In a 2008 study, the National Toxicology Program found that chromium-6 increased the risk of cancer in laboratory animals, including gastrointestinal tumors.

The debate now centers on whether chromium-6 is as toxic in water as it is in the air. There isn’t a lot of data on swallowing the compound, although it is known to cause cancer if it is inhaled.

The American Chemistry Council and the American Water Works Association are urging the EPA to hold off on setting rules until an industry-funded study is published next year, according to the New York Times.

Source: Environmental Working Group, New York Times

Read more: State Water Resources Control Board: Frequently Asked Questions About PG&E’s Background Chromium Study in Hinkley,

Information on Chromium from Apple Valley Ranchos Water Company