Substance fact sheet
The background information page contains information and concepts that will be useful in understanding some of the issues surrounding the NPI. It is strongly recommended that you read this before reading the information presented below.
For an explanation of some of the terms used in this page, see the Glossary
| Substance name | Selenium & compounds |
| CASR number | 7782-49-2 |
| Molecular formula | Se |
| Synonyms | No synonyms. Selenium compounds include selenium (IV) oxide or selenium dioxide (CAS# 7446-08-4), selenium (VI) fluoride or selenium hexafluoride (CAS# 7783-79-1), selenium (II) hydride or hydrogen selenide (CAS# 7783-07-5), selenium (IV) oxychloride (CAS# 7791-23-3), selenium (IV) sulfide or selenium disulfide (CAS# 7488-56-4), selenic acid (CAS# 7783-08-6), and selenous acid (CAS# 7783-00-8). |
Physical and chemical properties Physical properties: Selenium 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. Atomic Number: 34 Atomic Mass: 79.0 Melting Point (°C): 221 (grey selenium) Boiling Point (°C): 685 Specific Gravity: 4.4-4.8 Properties vary widely depending on the particular compound. Some physical properties for selected selenium compounds follow.
Chemical properties:
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Common uses Industry uses selenium to manufacture photocells, photographic exposure meters, solar cells, and rectifiers for home entertainment equipment. Further uses are in metal alloys, xerography, red or black glass, anti-dandruff shampoos, pigments in plastics, paints, dyes, enamels, inks, textiles, rubber (accelerator and vulcanising agent), photographic emulsions, and petroleum. It is also used in veterinary medicine, in medical therapeutic agents, as a nutritional feed additive for poultry and livestock, and as a fungicide and insecticide. Uses in electronics and photography account for the majority of selenium use, followed by the glass industry, then pigments. Some applications for specific selenium compounds follow. Selenium dioxide is the most widely used selenium compound in industry. It is used as an oxidising agent in drug and other chemical manufacture, a catalyst in organic syntheses, and an anti-oxidant in lubricating oils. Selenium sulfide is used in anti-dandruff shampoo. Selenous acid can be found in gun blueing solution which is used to clean the metal parts of a gun. |
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Sources of emissions Point sources Selenium compounds are released to the air and water in flue gas and fly ash during the combustion of coal and petroleum fuels (e.g. in coal-fired power stations), during the smelting and refining of metals such as copper, lead and zinc, from glass and ceramics manufacturing, and from refuse incinerators. It also accumulates in the residues from sulphuric acid manufacture. Diffuse sources, and point sources included in aggregated emissions data Selenium can enter waterways through use of some anti-dandruff shampoos. Application as fungicides and insecticides may contribute to elevated selenium levels in the environment. Electronic and photographic waste, and photocopying accessories may be other contributors if improperly disposed of. Cigarette smoke may be another source of selenium in air. Natural sources Selenium is a naturally occurring element, widely but unevenly distributed in the earth's crust and commonly found in sedimentary rock formations. However, there are no true deposits of selenium from which selenium can be directly and economically recovered. Selenium usually occurs combined with other compounds in the environment, such as in sulfide ores of other metals (silver, copper, lead, and nickel). Soils in the neighbourhood of volcanos tend to have enriched amounts of selenium. It occurs in water as a result of natural weathering of soils and rocks. Selenium is enriched in coal. Mobile sources Emissions may result from burning petrol in cars. Consumer products which may contain Selenium and compounds Anti-dandruff shampoos, home entertainment equipment, photographic equipment. |
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Health effects How might I be exposed to Selenium and compounds? Food is the primary source of exposure to selenium. Humans are usually breathing very low levels of selenium in air. Drinking water usually contains selenium at very low levels. Higher levels of selenium may be found in drinking water, usually in areas where high levels of selenium in soil contribute to the selenium content of the water. Occupational exposure to selenium in the air may occur in the metal industries, selenium recovery processes, painting, and special trades. Higher selenium levels may be encountered when living in the vicinity of these industries. By what pathways might Selenium and compounds enter my body? Selenium can be inhaled or ingested. Relative health hazard On a health hazard spectrum of 0 - 3 Selenium and compounds registers 1.7. A score of 3 represents a very high hazard to health, 2 represents a medium hazard and 1 is harmful to health. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the evaluation of its tendency to cause, or not cause cancer and/or birth defects. It does not take into account exposure to the substance. Human exposure is reflected in the NPI rank given to this substance (see comparative data below). A substance that scores highly as a health hazard is arsenic at 2.3 and one of the lowest scores is ammonia at 1.0.  Health guidelines Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996): Maximum of 0.01 mg/L (i.e. 0.00001 g/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. See the Additional Information page for current health information. The Australian NOHSC National Exposure Standards Database link is probably the most useful source of information. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Selenium and compounds have on my health? The severity of health effects will depend on how much selenium a person has been exposed to, for how long, the nature of the selenium compound(s), and current state of health. Trace amounts of selenium are essential for humans and most diets usually provide enough selenium to meet the daily requirement. Diets lacking selenium have resulted in heart problems and muscle pain. Diets with too much selenium can be harmful at levels 5 to 10 times higher than the daily requirement. Accidentally swallowing a large quantity of selenium supplement pills could be life-threatening without immediate medical treatment. Eating too much selenium over long periods of time can result in excessive tooth decay, discolouration of the skin and teeth, brittle hair, deformed nails, fatigue, irritability, depression and pallor. Feeling and control in the arms and legs may also be lost. People exposed to very high levels of selenium in the workplace have reported headaches, dizziness, fatigue, irritation (eye, nose, throat and bronchial tubes), collection of fluid in the lungs, and severe bronchitis. The exact levels at which these effects occur are not known. Upon contact with skin, selenium compounds have caused rashes, swelling, and pain. It may also protect against the toxicity of heavy metals such as cadmium, mercury and silver. More details about two selenium compounds follow. Selenium sulfide is very different from the selenium compounds found in foods and in the environment. Selenium sulfide has not caused cancer in animals when it is placed on the skin, and the use of anti-dandruff shampoos containing selenium sulfide is considered safe. When ingested it is reasonably anticipated to be a carcinogen. Selenium hydride is the most acutely toxic selenium compound, resembling arsenic in its physiological reactions. Acute (short term) exposure to selenium hydride by inhalation results primarily in respiratory effects, such as irritation of the mucous membranes, collection of fluid in the lungs, severe bronchitis, and bronchial pneumonia. |
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Environmental effects Environmental Fate Small selenium particles in the air settle to the ground or are taken out of the air by rain. Soluble selenium compounds can be found in natural waters, either as selenites or selenates. Environmental Transport Selenium can be transported as particles released into the atmosphere or as dissolved compounds in natural waters. Relative hazard to the environment On an environmental spectrum of 0 - 3 Selenium and compounds registers 1.8. A score of 3 represents a very high hazard to the environment and 0 a negligible hazard. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the measure of its ability to remain active in the environment and whether it accumulates in living organisms. It does not take into exposure to the substance. Environmental exposure is reflected in the NPI rank for this substance (see comparative data below). A substance that scores highly as an environmental hazard is oxides of nitrogen at 3.0 and one of the lower scores is carbon monoxide at 0.8.  Environmental guidelines Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992): Maximum of 5 microgram/L (i.e. 0.000005 g/L) and 70 microgram/L (i.e. 0.00007 g/L) in marine waters respectively. See the Additional Information page for current environmental guidelines. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Selenium and compounds have on the environment? Trace amounts of selenium are essential for animals, but selenium is generally not essential for plants. Many plants are selenium tolerant. The toxicity of selenium depends on whether it is in the biologically active oxidised form. This form can be found in alkaline soils, causing plant uptake of the metal to be increased. Various plants are known to accumulate selenium. The biological availability appears to be reduced in acidic or neutral soils. Some plants and micro-organisms can volatilise selenium from soils by converting selenium to volatile alkylated selenium compounds. Plants containing high levels of selenium and selenium compounds can be toxic to grazing livestock. "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. "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. In waters containing elevated levels of selenium fish can bioaccumulate selenium, building up high levels. Selenium and its compounds have high acute toxicity to aquatic life and mammals and moderate acute toxicity to birds. Insufficient data are available to evaluate or predict the short term effects of selenium on plants. |
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Comparative data NPI Rank Approximately 400 substances were considered for inclusion on the NPI reporting list. A risk ranking was given based on health and environmental hazard identification and human and environmental exposure to the substance. Some substances were grouped together at the same rank with 208 ranks in total. Selenium and compounds was ranked as 85 out of the 208 ranks. Total hazard score (human health + environmental criteria) = 3.5.  |
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Sources of information used in preparing this article
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