11 Things You Need to Know About the Carcinogen Discovered in Drinking Water

When you see news reports about a cancer-causing chemical in drinking water everywhere you turn, you probably have a few questions. Of course you can read EWG's full report, but on the off chance you're pressed for time and just want to know the basics, we put together these 11 questions and answers.

1. What is hexavalent chromium?

Hexavalent chromium (or chromium-6) is a highly toxic form of the naturally occurring metal chromium. It is a well-known human carcinogen when inhaled, and recent evidence indicates it can cause stomach or gastrointestinal cancer when ingested in drinking water. However, a different form, trivalent chromium, is an essential nutrient.

People typically are exposed to chromium-6 by consuming contaminated water or food, and in some workplaces by breathing contaminated air. That's a concern especially for those working in metallurgy or leather-tanning facilities. Ingesting or inhaling contaminated soil particles may also be a source of exposure. Widespread industrial use has led to detections of hexavalent chromium in two-thirds of current or former Superfund toxic waste sites.

2. How does it get into tap water?

Chromium-6 can get into water as a result of industrial contamination from manufacturing facilities, including electroplating factories, leather tanneries and textile manufacturing facilities, or from disposal of fluids used before 1990 in cooling towers. It also occurs naturally in some minerals. The widely used tap water disinfectant chlorine can transform trivalent chromium into the toxic hexavalent form.

3. Why is it a problem?

Exposure in tap water has been linked to cancers of the stomach and gastrointestinal tract in both animals and people. California's Environmental Protection Agency has issued a draft public health goal based on the conclusion that levels of chromium-6 greater than 0.06 parts per billion (ppb) in tap water may increase cancer risk.

Some people may be especially susceptible. Fetuses, infants and children are more sensitive to carcinogenic chemicals. In addition, people with less acidic stomachs appear to have a limited ability to convert chromium-6 to the benign trivalent form (chromium-3), putting them at greater risk. Using common antacids and proton pump inhibitors can lower stomach acidity. Other conditions that can inhibit stomach acid production include infection with Helicobacter pylori (a common bacterium linked to ulcers), pernicious anemia, pancreatic tumors, mucolipidosis type IV and some autoimmune diseases.

4. How can I find out if my tap water has hexavalent chromium in it?

California requires water utilities to test and report levels of chromium-6 in their water. For Californians, this is a good way to find out if this contaminant is a concern in your area. Unfortunately, these tests only measure levels at or above 1 ppb, more than 16 times above the suggested public health goal of 0.06 ppb.

Of the 438 community water sources in California that have provided test data to EWG, 223 detected levels above 1 ppb, and 93 detected levels above 5 ppb. This means more than 13.7 million Californians drink tap water contaminated with chromium-6.

Elsewhere, water utilities only test and report levels of total chromium -- which includes both the toxic form and the essential nutrient chromium-3. Moreover, these tests only detect levels at or above 10 ppb, more than 160 times higher than California's proposed public health goal. If your tap water has detectable levels of total chromium, it's quite possible that it has levels of hexavalent chromium that exceed California's suggested public health goal. The ratio of chromium-3 to chromium-6 varies in different water supplies, so it is difficult to estimate how much of each might be in your water.