Chromium is an odorless and tasteless metallic element. Chromium is found naturally in rocks, plants, soil and volcanic dust, and animals. The most common forms of chromium that occur in natural waters in the environment are: Trivalent chromium (chromium-3) and Hexavalent chromium (chromium-6). Trivalent chromium is an essential trace element for humans. Together with insulin it removes glucose from blood, and it also plays a vital role in fat metabolism. Chromium deficits may enhance diabetes symptoms. Chromium (III) toxicity is unlikely, at least when it is taken up through food and drinking water. It may even improve health, and cure neuropathy and encephalopathy. However, hexavalent chromium is known for its negative health and environmental impact, and its extreme toxicity. It causes allergic and asthmatic reactions, is carcinogenic and is 1000 times as toxic as trivalent chromium. Health effects related to hexavalent chromium exposure include diarrhoea, stomach and intestinal bleedings, cramps, and liver and kidney damage. Toxic effects may be passed on to children through the placenta. Chromium (VI) compounds are divided up in water hazard class 3, and are considered very toxic. If ingested as drinking water, hexavalent chromium (Cr-VI) is likely to be a carcinogen at a certain level, but studies are still being conducted to evaluate what level is unsafe and whether it does cause cancer or not. The United States Environmental Protection Agency (EPA) has a drinking water standard of 0.1 milligrams per liter (mg/L) or 100 parts per billion (ppb) for total chromium.