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Selenium


What is Selenium?

 

Selenium is a naturally occurring mineral that is distributed widely but unevenly in nature in the earth�s crust.   It is commonly found in rocks and soils.   In its elemental form, selenium is found as metallic gray to black crystals.   However, selenium is not often found in the environment in its elemental form, but is usually combined with other substances.   Much of the selenium in rocks is combined with sulfide minerals or with silver, copper, lead, and nickel minerals.   Selenium also combines with oxygen to form several white or colorless crystals.

 

Are there commercial uses for selenium?

 

Most selenium is used in the electronic industry, but it is also used:

 

  • In the glass industry

 

  • As a nutritional supplement

 

  • As a nutritional feed additive for poultry and livestock

 

  • In the preparation of pharmaceuticals such as antidandruff shampoos,

 

  • As a component in the pigments in plastics, paints, enamels, inks, and rubber and,

 

  • As a constituent in fungicides

 

Radioactive selenium is used in diagnostic medicine

 

What happens to selenium when it enters the environment?

 

  • Selenium can be released into the environment by both natural and manufacturing processes.

 

  • Selenium dust can enter the air from burning coal and oil.   This dust will eventually settle over the land and water.

 

  • Selenium also enters water from agricultural and industrial activities

 

  • Some selenium compounds will dissolve in water, and some will settle to the bottom as particles.

 

  • Insoluble forms will remain in soil, but soluble forms are very mobile and may enter surface water from soils.

 

 

 

How are people exposed to selenium?

 

  • Consuming small amounts present in food and water or breathing air containing selenium.  

 

  • Breathing burning smoke from burning coal or oil.

 

  • Living in areas with unusually high natural levels of selenium in rock and soils.

 

  • Working in a job that involves selenium production or use, such as pharmaceutical industry or pesticide application, and through the use of selenium containing consumer products.

 

How does selenium enter and leave the body?

 

�          In humans, selenium is easily absorbed from the gut following eating food or drinking water.

 

�          Selenium is also absorbed through the lungs during breathing.

 

�          Absorption through the skin is generally minimal, although toxic effects on the skin have resulted from direct contact.

 

�          Selenium can build up in the body if exposures are high or if they occur over a long period of time.   It builds up mostly in the liver and kidneys but also in the blood, lungs, heart, and testes.   Selenium can build up in the nails and in hair, depending on the length of time and amount of exposure.   Selenium has also been shown to be present in breast milk.    

 

�          Most of the selenium that enters the body quickly leaves the body, usually within 24 hours. Beyond what the body needs, selenium leaves mainly in the urine, but also in the feces and breath.

 

Can I be exposed to selenium at my place of employment?

 

�          People are not normally exposed to large amounts of selenium in the workplace.   However, occupations where people may be exposed to selenium in air include the metal industries, and paint manufacturing.  

 

�          Hazardous waste sites may be source of environmental exposures to selenium.

 

How can selenium affect my health?

 

  • Selenium has both beneficial and harmful effects.   Selenium is an essential nutrient for humans and very small amounts are needed in the body for good health.   However large amounts are toxic and can harm one�s health.

 

  • Selenium stimulates the immune system and may play a protective role against some forms of cancer.  The National Academy of Science�s National Research Council recommended dietary allowance for selenium for both men and women is 55 micrograms (mcg) per day.

 

  • The Food and Drug administration (FDA) warns that the daily intake of selenium should not exceed 400 mcg unless supervised by a physician.   

 

  • High blood levels (greater than 100 mcg/deciliter) of selenium can result in a condition called selenosis.   Symptoms of selenosis include nausea, vomiting, diarrhea, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage.

 

  • The U.S. Agency for Toxic Substances and Disease Registry (ATSDR) has determined that 5 mcgs of selenium per kilogram of body weight taken daily would not be expected to cause any adverse health effects if taken over a lifetime.

 

  • Skin contact with selenium may cause redness, rash, swelling, and pain.

 

  • Brief occupational exposure to the eyes of high concentrations of selenium may cause burning, tearing, and eye irritation.

 

How likely is selenium to cause cancer?


The International Agency for Research on Cancer (IARC) has determined that selenium and selenium compounds are not classifiable as to their relationship to cancer.   However, the U.S. Department of Health and Human Services (DHHS) has determined that selenium sulfide is reasonably anticipated to cause cancer due to evidence showing that it produced liver tumors in animals fed high levels.  

       

How can selenium affect children?


The health effects seen in children exposed to selenium are likely to be similar to the effects seen in adults.  

 

How can families reduce the risk of exposure to selenium?

 

  • Certain dietary supplements and shampoos contain selenium. These should be used according to the manufacture�s directions.  

 

  • Children living near waste sites that contain selenium or coal burning plants should be encouraged to wash their hands before eating and to avoid putting unwashed hands in their mouths.

 

Is there a medical test to show whether I�ve been exposed to selenium?

 

Urine and blood tests for selenium are most useful for people who have recently been exposed to high levels.   Normally, urine is expected to contain less than 100 mcg/L of selenium.   Urine levels of selenium greater than 100 mcg/L may indicate additional exposure.  

 

Toenail clippings can be used to determine longer-term exposure.    Urine and toenail clippings can determine if you have been exposed to above-average levels of selenium.   However, they cannot predict whether the selenium levels in your body will affect your health.

 

Regulatory and advisory standards

 

  • The EPA has set a limit of 50.0 parts per billion (50.0 ppb) or 50 micrograms per liter (50 �g/L) of public drinking water.    

 

  • The Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit (PEL) of 0.2 milligrams of selenium per cubic meter of workplace air (0.2 mg/m 3) for 8-hour shifts and 40-hour work weeks.

 

References:

ToxFAQs for selenium, U.S. Agency for Toxic Substances and Disease Registry.

Selenium - Dietary Supplement Fact Sheet, Office of Dietary Supplements, National Institutes of Health, Updated 8/1/2004.