Chromium is found naturally in rocks, plants, soil and volcanic dust, and animals. The most common forms of chromium that occur in natural water in the environment are trivalent chromium (chromium III) and hexavalent chromium (chromium VI). Chromium III is far less toxic than chromium VI. Chromium VI occurs naturally and can be produced by industrial processes. Dermal exposure to it may occur during the use of consumer products that contain chromium. It is a known human carcinogen. When inhaled, it can cause lung cancer. Oral exposure has been linked with ulcers and cancers of stomach and intestine in animal studies. Skin contact can cause ulcers.