Toxicology

3.  What is Selenium?
 Role of Se in Animals.
 Importance of Selenium.
 Pictorial representation of the interface of Se with soil, plant
and atmosphere.
 Selenium in Environment.
 What is Barium?
 Applications
 Barium in the Environment.
 Health Effects of Barium.
 Environmental Effects of Barium.

4. Selenium
o Selenium (Se) is an essential micronutrient for humans and animals, but
lead to toxicity when taken in excessive amounts. Selenium is a metalloid
belongs to group 16 (Oxygen Family) of the periodic table. Being member
of the same group of the periodic table.
Source of Selenium
o Plants are the main source of dietary Se, but essentiality of Se for plants is
still controversial. However, Se at low doses protects the plants from variety
of abiotic stresses such as cold, drought, desiccation, and metal stress.
Selenium act as Antioxidant
o In animals, Se acts as an antioxidant and helps in reproduction, immune
responses, thyroid hormone metabolism.
What is Selenium?

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o Selenium is chemically similar to sulfur, hence taken up inside the plants
via sulfur transporters present inside root plasma membrane, metabolized
via sulfur assimilatory pathway, and volatilized into atmosphere.
o Selenium induced oxidative stress, distorted protein structure and
function, are the main causes of Se toxicity in plants at high doses.
o Plants can play vital role in overcoming Se deficiency and Se toxicity in
different regions of the world, hence, detailed mechanism of Se
metabolism inside the plants is necessary for designing effective Se
phytoremediation and biofortification strategies.

6. Role of Se in
Animals
 Tragic instance of Se-toxicity in humans was observed in Hubei
Province, China after digesting Se rich plants.
o Livestock is threatened persistently due to weathering of Se-rich
bedrocks, and anthropogenic activities like irrigation and mining.
o Se toxicity lead to a condition called selenosis i.e.,
 garlic odor of the breath.
 gastrointestinal disorders.
 hair loss.
 sloughing of nails, and neurological damage.
o In extreme selenosis cirrhosis of the liver, pulmonary edema, or even
death can occur.

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 Causes of Selenium of Deficency
o Selenium deficiency causes Keshan disease i.e.,
 weakening of heart and also atrophy.
 degeneration.
 necrosis of cartilage tissue in the joints.

8. Importance of Selenium
o About 30 selenoproteins have been identified in animals, which play
important roles in antioxidant defense,
 DNA synthesis.
 Reproduction.
 Immune response.
 Formation of thyroid hormones.
o Apart from above roles, several studies have reported anticancerous effect
of Se against liver, pancreas, prostate, esophagus, and colon cancer.
o In some studies, cardiovascular risk was found to be associated with low
intake of Se and Se-enriched diet found to improve overall health conditions
in patients suffering from cardiovascular diseases.

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o Se helps in:
 Embryo implantation
 Placenta retention
 Reduces infertility by increasing sperm mobility
 Testosterone
 Sperm synthesis
o Selenoproteins like Glutathione peroxidase, Thioredoxin reductase play
important role as antioxidants in maintaining intracellular redox potential.
o Deiodinase is involved in thyroid hormone metabolism. Selenoprotein P
transports Se between tissues and is an important extracellular antioxidant
constitutes about 50% of plasma Se.

10. Pictorial representation of the interface of Se
with soil, plant and atmosphere
Figure.
o Selenium present in soil is transported inside the plant through sulfate
transporters present in the plasma membrane of root cells. It is then
assimilated to organic Se via sulfur metabolic pathway inside the plant
and volatilized as DMSe (Dimethylselenide) and DMDSe.

11. Selenium in Environment
 Selenium occurs naturally in sedimentary rocks formed during the
carboniferous to quaternary period.
o The occurrence of Se in soil depends upon type of soil, organic matter and
rainfall.
o Mountainous countries like Finland, Sweden, and Scotland are generally
deficient in soil Se content whereas Shale soils and dried regions of the
world are Se-rich regions.
o Countries like UK
 France,
 India,
 Belgium,
 Brazil, Serbia, Slovenia, Spain, Portugal, Turkey, Poland, Germany,
Denmark, Slovakia, Austria, Ireland, Greece, Netherlands, Italy, China,
Nepal, Saudi Arabia, Czech Republic, Croatia, Egypt, Burundi, and New
Guinea are reported to have Se deficient areas.

12. What is Barium?
 Barium (Ba) is an alkaline earth metal that is ubiquitously present at
low to moderate concentrations in the natural environment.
o Although Ba has always been present as a trace element in food and
drinking water, its industrial (e.g., petroleum industry, steel industry,
production of semiconductors) and medicinal use (e.g., agent for
taking radiographs of the gastrointestinal (GI) tract) have more than
doubled during the last 40 years.
o Barium is a silvery-white metal that can be found in the environment,
where it exists naturally. It occurs combined with other chemicals,
such as sulfur, carbon or oxygen. Ii is very light and its density is half
that of iron. Barium oxidizes in air, reacts vigoroulsy with water to form
the hydroxide, liberating hydrogen.

13. Applications
o Barium is often used in barium-nickel alloys for spark-plug
electrodes an in vacuum tubes as drying and oxygen-removing
agent.
o It is also used in fluorescent lamps: impure barium sulfide
phosphoresces after exposure to the light.
o Barium compounds are used by the oil and gas industries to make
drilling mud. Drilling mud simplifies drilling through rocks by
lubricating the drill.
o Barium compounds are also used to make paint, bricks, tiles,
glass, and rubber. Barium nitrate and clorate give fireworks a
green colour.

14. Barium in the Environment
 Barium is surprisingly abundant in the Earth's crust, being the 14th most abundant
element.
o High amounts of barium may only be found in soils and in food, such as nuts,
seaweed, fish and certain plants.
o Because of the extensive use of barium in the industries human activities add greatly
to the release of barium in the environment.
o As a result barium concentrations in air, water and soil may be higher than naturally
occurring concentrations on many locations.
o Barium enters the air during mining processes, refining processes, and during the
production of barium compounds. It can also enter the air during coal and oil
combustion.

15. Health Effects of Barium
 Many hazardous waste sites contain certain amounts of barium. People that
live near them may be exposed to harmful levels.
o The exposure will than be caused by breathing dust, eating soil or plants,
or drinking water that is polluted with barium. Skin contact may also occur.
o The health effects of barium depend upon the water-solubility of the
compounds. Barium compounds that dissolve in water can be harmful to
human health.
o The uptake of very large amounts of barium that are water-soluble may
cause paralyses and in some cases even death.

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o Small amounts of water-soluble barium may cause a person to experience
breathing difficulties, increased blood pressures, heart rhythm changes,
stomach irritation, muscle weakness, changes in nerve reflexes, swelling of
brains and liver, kidney and heart damage.
o Most human exposures to toxic Ba salts occur via ingestion or inhalation.
The most common toxic outcomes include:
 cardiac and/or renal failure.
 pulmonary edema.
 respiratory paralysis.
 gastric
 intestinal hemorrhages. .

17. Environmental Effects of
Barium
 Some barium compounds that are released during industrial processes
dissolve easily in water and are found in lakes, rivers, and streams.
 Because of their water-solubility these barium compounds can spread
over great distances. When fish and other aquatic organisms absorb the
barium compounds, barium will accumulate in their bodies.
 Because it forms insoluble salts with other common components of the
environment, such as carbonate and sulphate, barium is not mobile and
poses little risk.
 Barium compounds that are persistent usually remain in soil surfaces, or
in the sediment of water soils. Barium is found in most land soils at low
levels. These levels may be higher at hazardous waste sites.