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, while the more toxic form, chromium-6, is generally produced by industrial processes. Chromium-6 occurs naturally in the ground by may also enter drinking water sources, including groundwater, from historic leaks and industrial waste sites.
Chromium can change from chromium-3 to chromium-6, and vice versa, depending on the chemical and physical environment.