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
- Research conducted in collaboration with the Wisconsin Geological Survey strongly suggests that the chromium-6 found in Madison's water is naturally-occurring and has 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 one of the lowest rates in the state (2.5 per 100,000 people).
- Chromium-6 has been detected at low levels (less than 2 parts per billion) in 14 of Madison's 22 wells.
- In 2014, California was the first state in the nation to establish a regulatory standard for chromium-6, which was set at 10 parts per billion (ppb). Right now, there is no federal regulatory standard for the substance.
- Frequently Asked Questions about Chromium-6