Name: Caitlin Morris

1
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
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 Selenium-Se).
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 lt40µg-1
in your body is considered deficient and a dose
of gt400 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.
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.
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 2 Above is a prime example of Se
toxicity hair loss (Fordyce).
CASE STUDIES
HISTORY OF SELENIUM
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 mid-1800s (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).
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 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.
Figure 1 The blown up square of Selenium on the
Periodic Table. Located beneath Sulfur (16) and
above Tellurium (52) (Se on Periodic Table).
REFERENCES

• 1. Kashin-Beck Disease Picture.
  http//www.pathguy.com/lectures/kashin_beck.jpg
• 2. The Element Selenium. Its Elemental
  Jefferson Lab. http//education.jlab.org/itselemen
  tal/ele034.html
• 3. Se on the Periodic Table. http//pubs.usgs.go
  v/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//environmentalchemistr
  y.com/yogi/periodic/Se.html.

CONTACT
Name Caitlin Morris Organization
Western Oregon University Email
cmorris06_at_wou.edu
Figure 5 Above is a map of the distribution of
Keshan Disease in mainland China (Fordyce).