Inorganic arsenic is a poisonous substance that occurs when arsenic is combined with elements other than carbon. It can be released into the air and deposited into water and soil during events, such as forest fires, or through industrial operations, such as ore mining. Humans may be exposed to it by eating foods, such as rice, flour, and other grains, that were grown in contaminated soil or water. They may also be exposed to it through drinking water, particularly in areas where the groundwater is in contact with arsenic-containing minerals. Although the maximum level allowed in water is 10 µg/L in the United States, arsenic levels are commonly greater in some rural communities in the Southwest, Midwest, and Northeast. Long-term exposure to high levels of inorganic arsenic, such as through drinking water with greater than 100 µg/L, is known to increase the risk for cardiovascular disease. Less is known about the cardiovascular effects of long-term exposure to low to moderate levels (> 10 µg/L but <100 µg/L).