Selenium in Soil

In Soil

• Soils in most of the Midwest United States contain adequate selenium content, according to Cornell University. Areas in the East and Northwest often have low levels. The amount of selenium varies greatly from location to location. The trace element remains in the soil until absorbed by a plant. From there it can enter the food chain. County extension offices offer maps of soil selenium levels in areas where it is a problem. Soil testing also quantifies the level of selenium in an individual field.

In Plants

• Most plants accumulate only trace amounts of selenium, but there are exceptions. Plants in the genus Astragalus, this includes the vetches and locoweed, accumulate selenium to toxic levels. These plants commonly have an odor and bitter taste and are usually only consumed by animals as a last resort. Forage crops such as alfalfa commonly accumulate about 0.35 milligrams of selenium per kilogram, while wheat varies from 0.05 to 0.45 mg/kg.

Selenium Deficiency

• Diets deficient in selenium lead to nutritional muscular dystrophy, commonly known as white muscle disease in livestock. In humans, symptoms of deficiency include muscle problems, including an increased risk of heart disease. Severe cases can result in mental disabilities and even death. Farmers feed livestock selenium-rich supplements if the natural forage in their area is low in selenium. Vegetables grown in soils containing selenium are the most common source of the trace element for humans. Supplements such as wheat germ and enriched breads also contain selenium.

Excess Selenium

• Excess selenium in livestock leads to death within hours in acute poisoning cases. Long-term exposure results in what ranchers refer to as the "blind stagger," which is often fatal if allowed to progress. No treatment other than removing the high-selenium feed is available. Human selenium poisoning symptoms include stomach problems, hair loss and possible nerve damage.