By David Deming

According to a recent report by the Environmental Working Group, drinking water in Norman, Oklahoma, contains the highest level of chromium 6 in the US, 12.9 parts per billion. Chromium 6 is a known carcinogen, but its relatively high level in Norman city water is unlikely to be a health problem.

Toxicity depends on dosage. Any substance -- even distilled water -- is potentially toxic when consumed in large quantities. In 2007, a twenty-eight-year-old woman died of water intoxication after drinking too much bottled water. Selenium is a trace element that is known to be highly toxic. In 2006, an Australian man perished only six hours after consuming a mere ten grams of sodium selenite. But sodium selenite is also an essential nutrient that is sold as a dietary supplement in health food stores. People add small amounts of selenium to their diets because there is significant scientific evidence that ingestion of optimal amounts of this mineral reduces the incidence of cancer in animals. Substances that are toxic in large amounts can be beneficial and even essential when consumed in small amounts.

In the human body, chromium 6 is converted to the more common form of chromium 3 and vice versa. Chromium 3 is found in common foods such as bread, milk, and vegetables. People in the US daily obtain about a tenth of a milligram of chromium 3 in their diets. Chromium in involved in insulin metabolism, and it has been hypothesized that insufficient dietary intake of chromium 3 may contribute to the development of diabetes.

The primary evidence that chromium 6 causes cancer in humans is an epidemiological study from China where water was contaminated with chromium 6 levels up to 1550 times higher than the levels found in Norman city water. These high levels of chromium 6 were correlated with an increased incidence of stomach cancer. If chromium 6 in Norman water caused cancer, the stomach cancer rate in Cleveland County would be above average. But it is below average. Between 2003 and 2007, deaths from stomach cancer in Cleveland County were 2.7 per 100,000 population, twenty-nine percent lower than the US average of 3.7 per 100,000.

The mere fact that chromium 6 is a carcinogen should not be alarming. Carcinogens are not limited to environmental contaminants such as chromium 6. Many natural foods contain carcinogens. These include beer (ethyl alcohol), apples (caffeic acid), and peanut butter (aflatoxin). Coffee contains more than a thousand chemicals, half of which are carcinogenic. Trace amounts of carcinogenic substances do not commonly cause cancer because the human body contains defense enzymes that are effective against both natural and synthetic carcinogens.

When we exaggerate exotic risks, we divert attention and resources from common factors that are much more likely to cause premature death. The leading causes of premature morbidity are smoking, physical inactivity, poor diet, and automobile accidents. These are all preventable. We would all live longer and be healthier if we just applied some common sense, drove defensively, and took better care of our bodies.