Chromium is a metallic element found naturally in rocks, soil, plants, and animals -- including humans. It occurs in the environment and in drinking water sources in two principal forms: chromium-3 and chromium-6 (also called hexavalent chromium or hex chrome). The sum of all chromium in a sample is called total chromium.
Chromium-3 occurs naturally in many vegetables, fruits, meats, and grains and is an essential dietary nutrient. Chromium-6 is commonly found at low levels in drinking water. It can occur naturally in the ground but may also enter drinking water sources via industrial pollution.
Chromium can change from chromium-3 to chromium-6, and vice versa, depending on the chemical and physical environment.
CHROMIUM-6 IN MADISON'S WATER
- The chromium-6 found in Madison's water is naturally-occurring and has likely been present in the area's water for many generations.
- Although extremely high levels of chromium-6 in drinking water are thought to cause stomach cancer, Madison has a very low rate of the disease. The statewide rate of stomach cancer is well below the national average (3.8 per 100,000 people) and Dane County has the lowest rate in the state (2.5 per 100,000 people).
- Chromium-6 has been detected at low levels (less than 2 ppb) in 14 of Madison's 22 wells.
- Right now, there is no federal regulatory standard for Chromium-6, although the State of California is considering enacting its own regulatory limit of 10 ppb.