It's important you understand this information because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present. Selenium is an essential metal that helps prevent damage caused by oxygen. Most diets in the United States provide selenium at or above the daily requirement. Too much selenium can cause brittle hair, deformed nails, and loss of feeling and control in the arms and legs.
Selenium is a metal commonly found in rocks and soil.
In the environment, selenium is not often found in the pure form. Much of the selenium in rocks is combined with sulfide minerals or with silver, copper, lead, and nickel minerals. Selenium and oxygen combine to form several compounds. Industrially produced hydrogen selenide is a colorless gas with a disagreeable odor. It is probably the only selenium compound that might pose a health concern in the workplace.