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Minerals in Detail
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
SELENIUM
Selenium - chemical details
| Symbol | Se |
| Atomic number | 34 |
| Atomic mass | 78.96 g.mol-1 |
| Electronegativity | 2.4 (according to Pauling) |
| Density | 4.79 g.cm-3 at 20°C |
| Melting point | 217 °C |
| Boiling point | 688 °C |
| Vanderwaals radius | 0.14 nm |
| Ionic radius | 0.198 nm (-2) |
| 0.042 nm (+6) |
| Isotopes | 9 |
| Electronic configuration | [ Ar ] 3d10 4s2 4p4 |
| Energy of first ionisation | 940,7 kJ.mol-1 |
| Energy of second ionisation | 2045 kJ.mol-1 |
| Energy of third ionisation | 2973.7 kJ.mol-1 |
| Standard potential | - 0.77 V |
| Discovered | 1817 - Jons Berzelius |
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
Selenium - Description
Selenium is a non-metallic member of group XVI of the periodic table. In chemical activity and physical properties it resembles sulfur and tellurium.
Selenium appears in a number of allotropic forms: the most common are a red amorphous powder, a red crystalline material, and a grey crystalline metal-like
form called metallic selenium. This last form conducts electricity better in the light than in the dark and is used in photocells. Selenium burns in air and
is unaffected by water, but dissolves in concentrated nitric acid and alkalis.
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
Selenium - Industrial applications
Selenium is used in electronics, glass, photocopying, rubber, and food supplements. For details on
industrial applications and impact on the environment see www.lenntech.com/Periodic-chart-elements/Se-en.htm
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
Selenium - In natural form
Selenium is rare, less common than silver. Selenium is present in the atmosphere as methyl derivatives. Pure selenium is unusual, but there are around 40
known minerals with a selenium content, some with as much as 30% selenium - but all are rare and generally they occur together with sulphides of metals such
as copper, zinc and lead. The main producing countries are Canada, USA, Bolivia and Russia. Global industrial production of selenium is around 1500 tonnes a
year and about 150 tonnes of selenium are recycled from industrial waste and reclaimed from old photocopiers.
Selenium occurs naturally in the environment. It is released through both natural processes and human activities. Well fertilized agricultural soil
generally has about 400 mg/ton since the element is naturally present in phosphate fertilizers and is often added as a trace nutrient. In its natural form
as an element selenium cannot be created or destroyed, but selenium does have the ability to change form.
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
Selenium - Impact on health
In humans, selenium is a trace element nutrient which functions as co-factor for reduction of antioxidant enzymes such as glutathione peroxidases, (which
metabolizes free radicals formed from the oxidation of polyunsaturated fatty acids) and certain forms of thioredoxin reductase. Glutathione peroxidase
(GSH-Px) catalyzes certain reactions which remove reactive oxygen species such as peroxide:
2 GSH+ H2O2---------GSH-Px = GSSG + 2 H2O
Selenium also plays a role in the functioning of the thyroid gland by participating as a co-factor for the three known thyroid hormone deiodinases.1
This enzymes deiodinates thyroid hormones, assisting the body’s use of this hormone. Selenium also functions as an antioxidant that works in conjunction
with vitamin E. One study determined that head and neck cancer patients had serum selenium levels that were significantly lower compared with controls, and
these levels decreased further as their tumor burden increased.2
Dietary selenium comes from nuts, cereals, meat, fish, and eggs. Brazil nuts are the richest ordinary dietary source (though this is soil-dependent, since
the Brazil nut does not require high levels of the element for its own needs). High levels are found in kidney, tuna, crab and lobster, in that order.3
Chemical Details | Description | Industrial Applications |
In Nature | Health Impacts | Daily Intake
Selenium - Recommended daily & maximum intake
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Risk free |
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intake? |
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Food sources? |
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Result of overdose? |
| Age Group |
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RDA |
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Limit |
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Infants
0-6 mo
7-12 mo
Children
1-3 y
4-8 y
Males
9-13 y
14-18 y
19-30 y
31-50 y
50-70 y
> 70 y
Females
9-13 y
14-18 y
19-30 y
31-50 y
50-70 y
> 70 y
Pregnancy
< 19 y
19-30 y
31+ y
Lactation
< 19 y
19-30 y
31+ y |
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(ug/d)
15.0
20.0
20.0
30.0
40.0
55.0
55.0
55.0
55.0
55.0
40.0
55.0
55.0
55.0
55.0
55.0
60.0
60.0
60.0
70.0
70.0
70.0 |
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(ug/d)
45.0
60.0
90.0
150.0
280.0
400.0
400.0
400.0
400.0
400.0
280.0
400.0
400.0
400.0
400.0
400.0
400.0
400.0
400.0
400.0
400.0
400.0 |
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Organ meats
Seafood
Vegetables (depending on soil selenium content |
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Hair brittleness
Hair loss
Nail brittleness
Nail loss |
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Explanations:
ND = Not determinable. There is either insufficient data on adverse effects and/or concern with the body's ability to handle excess amounts. In most
instances it is wise not to supplement for this particular element, but to rely on diet to provide sufficient quantities.
RDA = Recommended Dietary Allowance. May be used as a goal for daily intake. RDAs are set at a level that should meet the needs of 97-98% of all individuals.4, 5, 6, 7
Limit = The maximum level of daily nutrient intake from all sources that is highly likely to pose no risk of adverse effects.4, 5, 6, 7
References:
- Linus Pauling Institute at Oregon State University, http://lpi.oregonstate.edu/infocenter/minerals/selenium. Retrieved 23 Sep 2008.
- Yadav, S., Gera, A., Singh, I., & Chanda, R. (2002). Serum selenium levels in patients with head and neck cancer. J Otolaryngol 2002 Aug;31(4):216-9
- Barclay, M., MacPherson, A., & Dixon, J. (1995). Selenium content of a range of UK food. Journal of food composition and analysis 8: 307–318.
- Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (1997). Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. Food and Nutrition Board: Institute of Medicine.
- Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (1998). Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6,
Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Food and Nutrition Board: Institute of Medicine.
- Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (2000). Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Food and Nutrition Board: Institute of Medicine.
- Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Food and Nutrition Board: Institute of Medicine.
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