Selenium Deficiency and Toxicity in the Environment

TLDR: The relationship between environmental exposure and health has been investigated in this article, where the authors show that even soils containing adequate total amounts of selenium can still produce selenia-deficient crops if the sehenium is not in a form ready for plant uptake.

Abstract: Selenium (Se) is a naturally occurring metalloid element, which is essential to human and other animal health in trace amounts but is harmful in excess Of all the elements, selenium has one of the narrowest ranges between dietary deficiency ( 400μgay−1) (WHO 1996), which makes it necessary to carefully control intakes by humans and other animals, hence, the importance of understanding the relationships between environmental exposure and health Geology exerts a fundamental control on the concentrations of selenium in the soils on which we grow the crops and animals that form the human food chain The selenium status of populations, animals, and crops varies markedly around the world as a result of different geological conditions Because diet is the most important source of selenium in humans, understanding the biogeochemical controls on the distribution and mobility of environmental selenium is key to the assessment of selenium-related health risks High selenium concentrations are associated with some phosphatic rocks, organic-rich black shales, coals, and sulfide mineralization, whereas most other rock types contain very low concentrations and selenium-deficient environments are far more widespread than seleniferous ones However, health outcomes are not only dependent on the total selenium content of rocks and soils but also on the amount of selenium taken up into plants and animals—the bioavailable selenium This chapter demonstrates that even soils containing adequate total amounts of selenium can still produce selenium-deficient crops if the selenium is not in a form ready for plant uptake

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Contribution to Medical Geology Book
The Natural Environment - Selenium Deficiency and Toxicity – Process Related
Diseases
Fiona Fordyce
British Geological Survey
West Mains Road
Edinburgh
EH9 3LA
UK
fmf@bgs.ac.uk

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Glossary
Alkali Disease: Can affect animals ingesting feed with a high selenium
content and is characterized by dullness, lack of vitality,
emaciation, rough coat, sloughing of the hooves,
erosion of the joints and bones, anemia, lameness, liver
cirrhosis and reduced reproductive performance.
Apoptosis: Programmed cell death.
Blind Staggers: Blind staggers occurs in cattle and sheep ingesting high
concentrations of selenium and is characterized by
impaired vision leading to blindness, anorexia,
weakened legs, paralyzed tongue, labored respiration,
abdominal pain, emaciation and death.
Crust: The outermost solid layer of a planet or moon.
Cytochrome P
450
: Iron-containing proteins important in cell respiration as
catalysts of oxidation-reduction reactions.
Exudative Diathesis: Selenium deficiency in birds can cause this condition; it
is characterized by massive hemorrhages beneath the
skin as a result of abnormal permeability of the capillary
walls and accumulation of fluid throughout the body.

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Glutathione Peroxidase: A detoxifying enzyme in humans and animals that
eliminates hydrogen peroxide and organic peroxides, it
has a selenocysteine residue in its active site.
Homeostatic Control: The ability or tendency of an organism or cell to
maintain internal equilibrium by adjusting its
physiological processes.
Igneous Rocks: Formed from the cooling and solidification of molten rock
originating from below the Earth’s surface, includes
volcanic rocks.
Iodothyronine deiodinase: Selenoproteins responsible for the production and
regulation of the active thyroid hormone from thyroxine.
Kashin-Beck Disease: An endemic osteoarthropathy (stunting of feet and
hands) causing deformity of the affected joints, occurs
in Siberia, China and North Korea.
Keshan Disease: An endemic cardiomyopathy (heart disease) that mainly
affects children and women of childbearing age in
China.

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Metamorphic Rocks: Formed from the alteration of existing rock material due to
heat and/or pressure.
Phytotoxicity: Toxic to plants.
Sedimentary Rocks: Formed by compression of material derived from the
weathering or deposition of eroded rock fragments, marine
or other organic debris or chemical precipitates from over-
saturated solutions.
Selenocysteine: An unusual amino acid of proteins, the selenium
analogue of cysteine, in which a selenium atom replaces
sulfur.
Selenomethionine: 2-amino-4- (methylseleno) butanoic acid.
Selenosis: Selenium toxicity.
Triiodothyronine: Also referred to as 3:5,3' triiodothyronine (T
3
) produced
in the thyroid gland and involved in controlling the rate
of metabolic processes in the body and physical
development.
Thyroxine: Also referred to as 3:5,3':5' tetraiodothyronine (T
4
) is
the major hormone secreted by the thyroid gland. T
4
is

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involved in controlling the rate of metabolic processes
in the body and influencing physical development.
Vadose Zone: Also known as the ‘unsaturated zone’ is the part of the
Earth’s surface extending down to the water table.
White Muscle Disease: This is a complex condition, which is multi-factorial in
origin but linked to selenium deficiency and causes
degeneration of the muscles in a host of animal species.
In lambs born with the disease, death can result after a
few days. Later in life, animals have a stiff and stilted
gait, arched back are not inclined to move about, lose
condition, become prostrate and die.
I. Summary
Selenium (Se) is a naturally occurring metalloid element, which is essential to human
and other animal health in trace amounts but is harmful in excess. Of all the elements,
selenium has one of the narrowest ranges between dietary deficiency (< 40 µg day
-1
)
and toxic levels (> 400 µg day
-1
) making it necessary to carefully control intakes by
humans and other animals hence the importance of understanding the relationships
between environmental exposure and health. Geology exerts a fundamental control on
the concentrations of selenium in the soils on which we grow the crops and animals
that form the human food chain and the selenium status of populations, animals and

Frequently asked questions

Q1. What is the role of selenium in the body?

Selenium forms a vital constituent of the biologically important enzyme glutathione peroxidase* (GSH-Px), which acts as an anti-oxidant preventing oxidative cell degeneration. 

Q2. What are the future works in this paper?

In the future, closer collaboration between medical and environmental scientists will be required to evaluate the real environmental health impact of this remarkable element in diseases such as cancer, AIDS and heart disease. 

Q3. What is the definition of blind staggers?

Blind Staggers: Blind staggers occurs in cattle and sheep ingesting highconcentrations of selenium and is characterized by impaired vision leading to blindness, anorexia, weakened legs, paralyzed tongue, labored respiration, abdominal pain, emaciation and death. 

Q4. What is the main topic of this chapter?

Since diet is the most important source of selenium in humans, understanding the biogeochemical controls on the distribution and mobility of environmental selenium is key to the assessment of selenium-related health risks. 

Q5. What is the main reason for the deficiency of selenium in the body?

Recent research has shown that selenium deficiency also adversely affects thyroid hormone metabolism, which is detrimental to growth and development. 

Q6. What is the name of the enzyme?

Glutathione Peroxidase: A detoxifying enzyme in humans and animals thateliminates hydrogen peroxide and organic peroxides, it has a selenocysteine residue in its active site. 

Q7. What is the definition of a selenite deficiency?

Disease: Can affect animals ingesting feed with a high seleniumcontent and is characterized by dullness, lack of vitality, emaciation, rough coat, sloughing of the hooves, erosion of the joints and bones, anemia, lameness, liver cirrhosis and reduced reproductive performance. 

Q8. What is the name of the chemical that causes the toxicity of tetraio?

Triiodothyronine: Also referred to as 3:5,3' triiodothyronine (T3) producedin the thyroid gland and involved in controlling the rate of metabolic processes in the body and physical development. 

Q9. What is the common condition in lambs?

Later in life, animals have a stiff and stilted gait, arched back are not inclined to move about, lose condition, become prostrate and die. 

Q10. What is the common cause of selenium deficiency?

High selenium concentrations are associated with some phosphatic rocks, organic-rich black shales, coals and sulfide mineralization whereas most other rock types contain very low concentrations and selenium deficient environments are far more widespread than seleniferous ones. 

Q11. What are the main health problems that can arise from selenium deficiency?

approximately 20 essential selenoproteins have now been identified in microbes, animals and humans, many of which are involved in catalytic functions in the body and selenium deficiency has been implicated in a host of conditions including cancer, heart disease, immune system function and reproduction. 

Q12. What is the name of the enzyme responsible for the production andregulation of the active thyroid hormone?

Iodothyronine deiodinase: Selenoproteins responsible for the production andregulation of the active thyroid hormone from thyroxine. 

Q13. What is the link between selenium deficiency and muscular weakness?

In animals, selenium deficiency has been linked to muscular weakness and muscular dystrophy but also causes reduced appetite, poor growth and reproductive capacity and embryonic deformities. 

Q14. What is the name of the plant?

Igneous Rocks: Formed from the cooling and solidification of molten rockoriginating from below the Earth’s surface, includes volcanic rocks. 

Q15. What are the main causes of selenium deficiency in humans?

Selenium deficiency has also been implicated in the incidence of a heart disorder (Keshan disease*) and bone and joint condition (Kashin-Beck disease*) in humans in various parts of China. 

Q16. What was the first evidence of selenium in animals?

selenium was identified as an essential trace element during pioneering work into selenium-responsive diseases in animals in the late 1950s and early 1960s. 

Q17. What is the name of the seleno acid?

Sedimentary Rocks: Formed by compression of material derived from theweathering or deposition of eroded rock fragments, marine or other organic debris or chemical precipitates from oversaturated solutions.