Selenium (Se) is an essential trace element for humans. It is found in the enzyme glutathione peroxidase. This enzyme protects the organism against certain types of damage. Some data suggest that Se plays a role in the body's metabolism of mercury (Hg). Selenium has in some studies been found to reduce the toxicity of Hg salts. Selenium and Hg bind in the body to each other. It is not totally clear what impact the amount of Se has in the human body on the metabolism and toxicity of prolonged Hg exposure.