Selenium is usually found in plant foods that are grown in soil that have a high selenium content. Nebraska and the Dakotas have very high levels of selenium versus China and Russia which have extremely low levels. Of course selenium can be found in meats and seafood because the animals eat the grains and plants that are grown in these soils and the selenium is stored in the animal's muscles. The Brazil nut has high level of selenium. It contains as much as 544 micrograms per ounce. Other foods such as mushrooms, tuna, beef and cod are good sources of selenium.
Selenium is very toxic in large doses and exceeding the Tolerable Upper Intake Level which is 400 micrograms per day (for adults) can be fatal. The Tolerable Upper Intake Lever was discovered by a study done on five Chinese patients in 1986 that had eaten corn grown in extremely selenium rich stony coal. Exceeding this level can lead to selenosis. Selenosis is seen a lot in live stock because of them ingesting selenium found in plants grown in the areas where they are grazing. Selenosis symptoms are gastrointestinal disorders, sloughing or white blotchy nails, garlic odor on the breath, fatigue, irritability and neurological damage. Extreme cases can result in cirrhosis of the liver, pulmonary edema and death.