Selenium

2021-08-27

Selenium is a chemical element with symbol Se and atomic number 34. [1] It is an odourless metalloid (an element which has both metallic and non-metallic properties). It can be a grey (the ‘metallic’ and most stable form), red or black solid. [2] In nature selenium is usually combined with sulphide minerals or with silver, copper, lead, and nickel. [3]

Uses [4]

Selenium has good photovoltaic and photoconductive properties, and it is used extensively in electronics, such as photocells, light metres and solar cells. The second largest use of selenium is in the glass industry: selenium is used to remove colour from glass, to give a red colour to glasses and enamels. The third main use is sodium selenite for animal feeds and food supplements. In addition, selenium can find applications in photocopying, in the toning of photographs. Its artistic use is to intensify and extend the tonal range of black and white photographic images. Other uses of selenium are in metal alloys such as the lead plates used in storage batteries and in rectifiers to convert AC current in DC current. Selenium is used to improve the abrasion resistance in vulcanised rubbers. Some selenium compounds are added to anti-dandruff shampoos.

Sources & Routes of Exposure

Sources of Exposure [4]

Selenium exposure takes place either through food or water, or through contact with soil or air that contains high concentrations of selenium. The exposure to selenium mainly takes place through food, because selenium is naturally present in grains, cereals and meat. Humans need to absorb certain amounts of selenium daily, in order to maintain good health. Food usually contains enough selenium to prevent disease caused by shortages. Selenium uptake through food may be higher than usual in many cases, because in the past many selenium-rich fertilisers have been applied on farmland. In addition, people that live near hazardous waste-sites will experience a higher exposure through soil and air. Selenium from hazardous waste-sites and from farmland will end up in groundwater or surface water through irrigation. This phenomenon causes selenium to end up in local drinking water, so that exposure to selenium through water will be temporarily increased. People that work in metal industries, selenium-recovery industries and paint industries also tend to experience a higher selenium exposure, mainly through breathing. Selenium is released to air through coal and oil combustion. People that eat a lot of grains that grow near industrial sites may experience a higher exposure to selenium through food. Exposure to selenium through drinking water may be increased when selenium from hazardous waste disposals ends up in water wells. Exposure to selenium through air usually only occurs in the workplace.

Routes of Exposure [3]

  • Inhalation (breathing) – Not a significant route of exposure for the general population, but is the primary route of exposure for selenium workers.
  • Ingestion– Primary route of exposure for the general population via consumption of food.
  • Dermal – Not a significant route of exposure to selenium.

Health Effects [5]

Acute Effects

Acute exposure of humans via inhalation to selenium compounds (selenium dioxide, hydrogen selenide) results primarily in respiratory effects. Acute inhalation exposure to elemental selenium dust results in irritation of the mucous membranes in the nose and throat, producing coughing, nosebleeds, dyspnea, bronchial spasms, bronchitis, and chemical pneumonia. Gastrointestinal effects including vomiting and nausea; cardiovascular effects; neurological effects such as headaches and malaise; and irritation of the eyes were reported in humans acutely exposed to selenium compounds via inhalation. Acute human exposure to selenium compounds via the oral route has resulted in pulmonary oedema and lesions of the lung; cardiovascular effects such as tachycardia; gastrointestinal effects including nausea, vomiting, diarrhoea, and abdominal pain; effects on the liver; and neurological effects such as aches, irritability, chills, and tremors. “Blind staggers” disease is a disease in livestock that results from acute consumption of plants high in selenium. It is characterised by impaired vision, aimless wandering behaviour, reduced consumption of food and water, and paralysis. Acute animal tests in rats, mice, and guinea pigs, have shown hydrogen selenide to have extreme toxicity from inhalation exposure, sodium selenite to have extreme toxicity from oral exposure, and elemental selenium to have low toxicity from oral exposure.

Chronic Effects

No information is available on the chronic effects of selenium in humans from inhalation exposure. In epidemiological studies of populations exposed to high levels of selenium in food and water, discoloration of the skin, pathological deformation and loss of nails, loss of hair, excessive tooth decay and discoloration, garlic odour in breath and urine, lack of mental alertness, and listlessness were reported. “Alkali disease” is a disease in livestock resulting from chronic consumption of high levels of selenium; it is characterised by hair loss, deformation and sloughing of the hooves, erosion of the joints of the bones, anaemia, and effects on the heart, kidney, and liver. EPA has not established a Reference Concentration (RfC) for selenium. The Reference Dose (RfD) for selenium is 0.005 milligrams per kilogram body weight per day (mg/kg/d) based on clinical selenosis in humans.

Selenium Deficiencies

Two diseases, “Keshan disease” and “Kashin-Beck disease” have been reported in humans in selenium-deficient populations in China. Keshan disease is characterised by heart failure, cardiac enlargement, abnormalities of EKG, and cardiogenic shock. Kashin-Beck disease, which occurs primarily in children between the ages of 5 and 13 years, is characterised by atrophy, degeneration, and necrosis of cartilage tissue. Some epidemiological studies have suggested that selenium deficiency may contribute to cardiovascular disease in humans. However, these studies are inconclusive due to confounding factors.

Reproductive/Developmental Effects

No information is available on the developmental or reproductive effects of selenium in humans. The consumption of high levels of selenium in the diet by pigs, sheep, and cattle has been shown to interfere with normal foetal development and to produce foetal malformations. Sodium selenate, administered in the drinking water to mice, did not result in birth defects, but did result in an increased incidence of foetal deaths and a high proportion of runts, while chronic exposure of mice to selenium in the diet has been shown to affect their fertility and to reduce the viability of the offspring of pairs that are able to breed.

Cancer Risk

In one study of workers exposed to selenium (form not specified) over a 26-year period, no statistically significant increase in cancer deaths was reported. Human studies have reported that patients with cancer, particularly gastrointestinal cancer, prostate cancer, or Hodgkin’s lymphoma, had significantly lower selenium levels in the blood than healthy patients. Epidemiological studies that used the selenium concentration in crops as an indicator of dietary selenium have generally reported an inverse association between selenium levels and cancer occurrence. Animal studies have reported that selenium supplementation, as sodium selenate, sodium selenite, and organic forms of selenium, results in a reduced incidence of several tumour types. The only selenium compound that has been shown to be carcinogenic in animals is selenium sulphide, which resulted in an increase in liver tumours in rats and mice and lung tumours in female mice from oral exposure. Selenium sulphide is a pharmaceutical compound used in anti-dandruff shampoos and is very different than the inorganic or organic selenium compounds found in foods and the environment. EPA has classified elemental selenium as a Group D, not classifiable as to human carcinogenicity, and selenium sulphide as a Group B2, probable human carcinogen.

Safety [6]

First Aid Measures

  • Eye Contact: Check for and remove any contact lenses. Do not use an eye ointment. Seek medical attention.
  • Skin Contact: After contact with skin, wash immediately with plenty of water. Gently and thoroughly wash the contaminated skin with running water and non-abrasive soap. Be particularly careful to clean folds, crevices, creases and groin. Cover the irritated skin with an emollient. If irritation persists, seek medical attention. Wash contaminated clothing before reusing.
  • Inhalation: Allow the victim to rest in a well-ventilated area. Seek immediate medical attention.
  • Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt or waistband. If breathing is difficult, administer oxygen. If the victim is not breathing, perform mouth-to-mouth resuscitation. Seek medical attention.
  • Ingestion: Do not induce vomiting. Loosen tight clothing such as a collar, tie, belt or waistband. If the victim is not breathing, perform mouth-to-mouth resuscitation. Seek immediate medical attention.

Exposure Controls & Personal Protection

Engineering Controls

Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits. If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.

Personal Protective Equipment

The recommended personal protective equipment includes:

  • Splash goggles;
  • Lab coat;
  • Dust respirator (be sure to use an approved/certified respirator or equivalent);
  • Gloves

Personal Protection in Case of a Large Spill:

  • Splash goggles
  • Full suit
  • Dust respirator
  • Boots
  • Gloves
  • A self-contained breathing apparatus should be used to avoid inhalation of the product
  • Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product

Regulation [2,6,7]

United States

  • EPA Office of Drinking Water regulates the amount of selenium allowed in drinking water. Public water supplies are not allowed to exceed 50 ppb total selenium.
  • FDA regulations allow a level of 50 ppb of selenium in bottled water.
  • OSHA exposure limit for selenium compounds in the air for an 8-hour period is 0.2 mg selenium/m3.

Australia

  • Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996): Maximum of 0.01 mg/L
  • Worksafe Australia has set the exposure standard for selenium compounds (excluding selenium hydride) to 0.2 milligram/m3 (TWA, as selenium). The exposure standard for selenium hydride and selenium hexafluoride is 0.05 ppm or 0.16 milligram/m3 (TWA, as selenium). Selenium and selenium compounds are classified as toxic by inhalation and if swallowed.

References

http://en.wikipedia.org/wiki/Selenium

http://www.npi.gov.au/substances/selenium/index.html

http://www.atsdr.cdc.gov/toxguides/toxguide-92.pdf

http://www.lenntech.com/periodic/elements/se.htm

http://www.epa.gov/ttn/atw/hlthef/selenium.html

http://www.sciencelab.com/msds.php?msdsId=9924874

http://www.atsdr.cdc.gov/PHS/PHS.asp?id=151&tid=28