16. Geochemical Controls on Selenium Occurrence in the Environment: Dietary
Balancing Between Deficiency and Toxicity
Caitlin Morris
Western Oregon University, Earth Science Department
ABSTRACT
INTRODUCTION
OCCURRENCE OF SE IN THE ENVIRONMENT
Recent advances in medical geology
have improved scientific understanding of
the role of selenium (Se) as an essential
trace element in human health. Even
though selenium is an essential element, it
has one of the narrowest concentration
ranges between physiological deficiency
and toxicity, either of which is potentially
detrimental to bodily function.
Se
deficiency is directly correlated with
Keshan Disease (KD), a heart ailment
mainly affecting women and children, and
Kashin-Beck Disease (KBD), which leads
to deformity of the feet and hands. The
effects of Se toxicity are less dramatic
than those associated with deficiency, but
just as efficient in causing health-related
discomfort. This project examines the role
of selenium geochemistry in human
health, and provides case examples of
public health issues from around the
world.
In perfect doses, Selenium is an essential
element that the human body needs in order to
function right. The only problem is that Selenium
has one of the smallest ranges of influence. The
symbol “µg” is a microgram, one of the smallest
units of weight. Having <40µg-1 in your body is
considered deficient and a dose of >400 µg-1 or
more of the element is considered a toxic dose
(Fordyce).
With a difference of 360 µg (or
micrograms), there is essentially little room for error
when Selenium is administered into the body either
through ingestion or airborne.
Location and the geological settings are the main
factors in determining Selenium toxicity or
deficiency. Most of the cases resulting from Se
toxicity or deficiency are found in developing
countries, mainly China and its subcontinent. This
poster will identify the main sources of Selenium and
how a person may become Se deficiency or toxic
because of those sources, three cases studies will
be reviewed regarding the health effects and a brief
history is also included.
HISTORY OF SELENIUM
CASE STUDIES
Selenium is found in almost all of the natural
materials
on earth, including soils, rocks, waters,
air, and plant and animal tissues (Fordyce). It is
constantly being recycled within the environment,
but vary rarely will you find Selenium by itself in its
elemental form.
Rocks and volcanoes produce more Selenium
than any other natural resource.
Selenium is
released from a volcano through the ash and gas
after volcanic activity (Fordyce). It is said that over
the course of history of the earth, volcanoes have
released an abundant 0.1 grams of selenium to
every cm2 (Fordyce). 0.1 grams is about six times
more than the selenium toxicity level.
With soils, one of the main causes of Selenium
deficiency is the leaching of the element out of the
soil. When leaching occurs, something is drawn out
of the soil, in this case, when selenium is drawn out
of the soil, it causes Kashin-Beck Disease or
Keshan Disease.
Volcanoes, rocks, and the
leaching of the soil are the natural processes in
which Selenium can be found and cause potential
harm.
The most common man-made process in which
Selenium is obtained is through the copper, lead,
and nickel refinery business (Element Selenium-Se).
Selenium is often a byproduct of those refinery
businesses. Today, around 600 tons of Selenium is
produced through the nickel, copper, and lead
refining business (Element Selenium-Se) and it is
mainly used in photoelectric cells, TV cameras, light
meters, copy machines, anti-dandruff shampoo, and
it also turns glass the color red (Element SeleniumSe).
Discovered by the Swedish chemist Jöns
Jacob Berzelius in 1817 (The Element
Selenium), it was quickly named after the
Greek word for “moon” (The Element
Selenium). Located in the number 34 spot
on the Periodic Table, Selenium has an
atomic weight of 78.96 and is classified as
a nonmetal and a chalcogen, which is also
known as the Oxygen family. Chemically,
Selenium is closely related to Sulfur and it
is rarely found in its elemental state in
nature.
Figure 1: The
blown up
square of
Selenium on
the Periodic
Table. Located
beneath Sulfur
(16) and above
Tellurium (52)
(Se on Periodic
Table).
CONTACT
Name: Caitlin Morris
Organization: Western Oregon University
Email: cmorris06@wou.edu
KESHAN DISEASE: Documented for over 100
years, but was not taken seriously until 1935 when a
major outbreak appeared in Keshan Country in
Northern China. Named after the county, Keshan
Disease is a type of heart disease that affects
mainly women and children of childbearing age in
mainland China. Keshan Disease (KD) can also
result in a decrease in heart function or lead to
severe heart enlargement which can result in death
(Fordyce). Refer to Figure 5, you will see the
distribution map of Keshan Disease throughout
China.
KASHIN-BECK DISEASE: Kashin-Beck Disease is
a disease that causes stunting in the arms and legs
of humans. Mainly found in China, Kashin-Beck
Disease (KBD) can also be found in Siberia and
North Korea.
Named after the two Russian
scientists who first described the disease in the mid1800s (Fordyce).
Kashin-Beck Disease can
commonly be found in the same region as Keshan
Disease, in the northern part of China (Fordyce).
SELENIUM TOXICITY: Selenium toxicity is a much
more rare occurrence than selenium deficiency. To
get Selenium poisoning involves a number of factors
including chemical form, concentration, and how the
chemical was introduced to the body, The main
health effects involved with Se toxicity are hair and
fingernail loss in big forms (Fordyce).
Figure 2: Above is a
prime example of Se
toxicity: hair loss
(Fordyce).
Figure 3: Above is the result of
Kashin-Beck Disease (KBD). It
resulted in the stunting of his
arms and legs (Kashin-Beck
Picture).
Figure 4: Above is an effect of Se toxicity: fingernail loss
(Fordyce).
CONCLUSIONS
At the right concentration, selenium is an essential
element for the human body. The physiological
effects of selenium toxicity and deficiency may be
extremely different, but both create an
uncomfortable lifestyle that have become an
everyday presence in China and in growing
locations around the world.
REFERENCES
Figure 5: Above is a map of the distribution of Keshan
Disease in mainland China (Fordyce).
1. “Kashin-Beck Disease Picture.
http://www.pathguy.com/lectures/kashin_beck.jpg
2. “The Element Selenium.” It’s Elemental: Jefferson Lab.
http://education.jlab.org/itselemental/ele034.html
3. “Se on the Periodic Table.” http://pubs.usgs.gov/of/2006/1184/1184.jpg
4. Fordyce, Fiona. “Selenium Geochemistry and Health.” Royal Swedish
Academy of Science 2007. 94.
5. “Element Selenium-Se.” Periodic Table of Elements. 1995-2010.
http://environmentalchemistry.com/yogi/periodic/Se.html.