National Drinking Water Clearinghouse
West Virginia University
PO Box 6893
The Villain of Hinkley, California
Chromium-6 Takes Center Stage
by Arjita Sharma NDWC Contributing Writer
Erin Brockovich movie photo reprinted with permission from Universal Studios.
If a chemical can claim to have had a starring role in an Oscar winning Hollywood production, it is chromium-6, also known as hexavalent chromium. Prior to the movie, Erin Brockovich, most people knew little about chromium. It took a rookie lawyers assistant, Erin Brockovich, to bring the villain of Hinkley, California, into the limelight a few years ago.
The Pacific Gas and Electric (PG&E) company used chromium-6 as an anti-corrosion agent in its compressor plant located in the San Bernadino County town of Hinkley. The leachate from the plant ended up contaminating the areas private groundwater wells.
Hinkley residents reported many health problems, ranging from minor skin irritations to cancer and birth defects. The ensuing legal battle ended in an out-of-court settlement of $333 million for the Hinkley population. Some cases, which might take many years to resolve, are still pending against PG&E in California courts.
However, ample dispute remains among the judges about whether the chemical deserves all the attention that it gets. The settlement, with regard to the Hinkley case, was not an indictment of chromium, but unwillingness on the parts of the two parties to drag the case through the courts. This article attempts to examine both sides of the chromium debate.
Chromium Has Two Roles
Chromium can occur in various forms, but trivalent chromium and hexavalent chromium are the most common forms found in the environment.
Trivalent chromium or chromium-3 occurs naturally and is a mineral essential to human health. It can be found in air, water, rocks, soil, and food items, such as broccoli, cheese, meats, cereal, brewers yeast, whole grains, and mushrooms.
Industrial processes produce hexavalent chromium or chromium-6. In this form, chromium has been linked to severe health problems, including lung cancer and cancer of the septum in the nasal passage. Chromium-6 can find its way into the environment if the industries that use chromium mismanage their waste streams.
Can I be exposed to it?
Chromium is present in trace amounts all around us. In air it can be found in amounts less that 0.1 micrograms per cubic meter. Natural levels in uncontaminated waters range from fractions of one microgram to a few micrograms per litre. Chromium can enter the body when breathed in contaminated air, ingested through water or food, or absorbed through skin when in soil, water, or air. As mentioned earlier, it exists in its non-toxic, essential form in some foods, too.
Chromium is brittle, hard, and lustrous in its metallic form. That is why it is used in stainless steel, chrome plating, and many alloys that require brittleness. An example is nichrome, an alloy used as a heating element in coffee pots, toasters, etc. Other uses for chemicals containing chromium are leather tanning, dyes, paints, refractory bricks, corrosion inhibitors, printing inks, photographic films, and wood preservatives.
Most individuals, such as factory workers, are exposed to chromium when they come in contact with polluted air in industrial situations. Besides people who work or live near industries that use chromium, tobacco users also are at risk to chromium exposure. When released in the water stream, chromium attaches itself strongly to soil and only small amounts can leach into groundwater. Most studies indicate that it is unlikely to cause adverse health effects when an individual is exposed to chromium in soil or water.
What can chromium do?
Chromium-3 is thought to play a major role in glucose metabolism. It is called the master regulator of insulin so that the body can use sugar, protein, and fat. People need 50 to 200 micrograms of chromium per day. Most diets do not contain adequate amounts of chromium. A deficiency can lead to an insulin imbalance in the body. Thus, chromium-3 is an essential mineral for physical well being. In fact, chromium is marketed as a supplement or as an ingredient in mineral water. Marketers claim that chromium promotes weight loss.
Hexavalent chromium, on the other hand, is a known carcinogen when breathed in large doses. The body accumulates chromium-6, especially in the lungs. Epidemiological and animal studies show that long-term exposure to amounts of chromium, 100 to 1,000 times greater than those existing naturally in air, seriously increases the risk of lung cancer. Short-term health effects include a runny, itchy nose; nosebleeds; and ulcers in the nasal-passage lining. High dosage, short-term exposure also can trigger asthma in those allergic to chromium.
When swallowed, it can cause stomach ulcers; damage to liver, kidney, circulatory, and nerve tissues; and skin irritation. However, in the stomach, gastric acids convert chromium-6 to its benign chromium-3 form. This nullifies damage it might have caused to the digestive system.
According to EPA, no evidence supports health problems, such as stomach or gastronomical cancer or birth defects, which the plaintiffs in the suit against PG&E attributed to chromium. Epidemiological studies of contaminated areas in San Bernadino County do not show proof of increased cancer risks or other ill effects.
Stringent guidelines exist as to how a sample must be tested for chromium-6. Further, testing is expensive, and very few labs test for chromium-6 in drinking water.
Testing for Chromium
Currently, EPA maintains a maximum contaminant level (MCL) of 0.1 parts per million (ppm) for total chromium. EPA believes, given present technology and resources, that this is the lowest level to which the agency can require water systems to reasonably remove this contaminant.
California maintains a .05 ppm MCL but has no guidelines for chromium-6. Also, any estimate of how much chromium-6 is in a sample cannot be based on total chromium, as this can vary greatly.
Stringent guidelines exist as to how a sample must be tested for chromium-6. Further, testing is expensive, and very few labs test for chromium-6 in drinking water. Testing for chromium-6 exposure through ingestion in the human system is not so easy either. The amount of chromium occurring naturally in the human body can vary depending upon its occurrence in the environment.
Further, since chromium-6 is converted to chromium-3 in the stomach, it is all the more difficult to reliably arrive at the level of chromium-6 exposure.
What does the government think?
Starting in the early 1990s, the furor over chromium-6 has only increased. However, due to a lack of literature on the subject, any guidelines with regard to chromium are rather arbitrary. The debate on chromium is particularly harsh in California.
The California Environmental Protection Agencys Office of Environmental Health Hazard Assessment formed a chromate toxicity review committee, which included many scientific experts. The committee wanted to provide guidance in determining an optimum drinking water level or public health goal for chromium-6 in drinking water. The committee concluded that no basis exists in either the epidemiological or animal data published that deduces orally ingested Cr (VI) [chromium 6] is a carcinogen.
In its report released in September 2001, the committee noted a lack of literature to support a case against or for chromium-6. The only lifetime exposure report available was a 1968 German study that researchers conducted on mice. But the study results are in doubt as the mice ended up contracting an infection that could have triggered the results. In addition, mice have a fore stomach that is non-acidic. Thus, unlike in a human stomach, chromium-6 is not converted to chromium-3 in the stomachs of mice.
Thus, chromiums effect on the mice cannot be extrapolated to humans. As a result, the committee recommended that researchers conduct a major study to determine an optimum drinking water level for chromium. In California, a state-level, five-year study is under way to determine a definitive standard for chromium-6.
Also, the committee noted that the current drinking water standard of 50 parts per billion (ppb) for total chromium includes the less toxic chromium-3, which poses no elevated public health risks. The World Health Organization also recommends a guideline of 50 ppb in its June 2000 International Standard for Drinking Water.
Treating Your Water for Chromium
As far as private wells are concerned, switching to bottled water is an option. EPA recommends the following options for treating water contaminated with chromium:
reverse osmosis, and
However, lower MCLs present a great financial burden to many treatment plants, especially small systems. Testing,
as well as treating for chromium, could prove to be an expensive proposition. Because it is not possible to properly estimate if the chromium is naturally occurring or due to environmental mismanagement, who should pay for the treatment
is also a controversial issue.
No Conclusive Proof Exists
So far, no conclusive proof exists regarding chromiums health effects. Some studies are underway that might settle the argument. As of now, the MCL that EPA set for total chromium stands. As for why PG&E settled out of court if the case could be made in their favor, many blame fear of adverse publicity. In addition, the study that the California EPA commissioned hadnt been released at that time.
About the Author
Arjita Sharma is a civil engineer by training, but a writer at heart. She currently lives in California with her family.
Report of the Chromate Toxicity Review Committee: (PDF File)
Agency For Toxic Substances And Disease Registry: Public health statement.
World Health Organizations stand on chromium: