VCE Environmental Science: Unit 4
Area of Study 1: Pollution
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"Heavy metals" is an inexact term used to
describe more than a dozen elements that
are metals or metalloids.
Examples of heavy metals include
chromium, arsenic, cadmium, lead, mercury
A metal of relatively high density, or of high
relative atomic weight.
Heavy metals occur naturally in the ecosystem
with large variations in concentration.
The primary anthropogenic sources of heavy
metals are point sources such as mines,
foundries, smelters, and coal-burning power
plants, as well as diffuse sources such as
combustion by-products and vehicle emissions.
Waste-derived fuels are especially prone to
contain heavy metals, so heavy metals are a
concern in consideration of waste as fuel.
Electronic waste is also a significant source of
heavy metal contaminants.
Because they cannot be degraded or destroyed,
heavy metals are persistent in all parts of the
Human activity affects the natural geological and
biological redistribution of heavy metals through
pollution of the air, water, and soil.
Humans also affect the natural geological and
biological redistribution of heavy metals by altering
the chemical form of heavy metals released to the
environment. Such alterations often affect a heavy
metal's toxicity by allowing it to bioaccumulate in
plants and animals, biomagnify in the food chain, or
attack specific organs of the body.
They are often stored as fat-soluble compounds in
Heavy metals are associated with myriad
adverse health effects, including
allergic reactions (e.g., beryllium, chromium),
neurotoxicity – affects nervous system(e.g., lead),
nephrotoxicity – affects kidneys(e.g., mercuric
chloride, cadmium chloride), and
cancer (e.g., arsenic, hexavalent chromium).
Humans are often exposed to heavy metals in
various ways—mainly through the inhalation of
metals in the workplace or polluted air, or
through the ingestion of food (particularly
seafood) that contains high levels of heavy
metals or paint chips that contain lead.
Living organisms require
varying amounts of
Iron, cobalt, copper,
and zinc are required by
humans. Excessive levels
can be damaging to the
Other heavy metals such as mercury,
plutonium, and lead are toxic metals that
have no known vital or beneficial effect on
organisms, and their accumulation over time
in the bodies of animals can cause serious
Certain elements that are normally toxic are,
for certain organisms or under certain
conditions, beneficial. Examples include
vanadium, tungsten, and even cadmium.
Cadmium has many
and the manufacture of
Exposure to cadmium can
occur in the workplace or
foodstuffs and can result
in emphysema, renal
disease, and perhaps
Humans discovered lead more
than 8,500 years ago, and over
time have used lead in artwork,
plumbing, gasoline, batteries, and
paint. Modern-day exposure to
lead occurs in the workplace or
through the ingestion of lead-
contaminated items such as paint
chips.The primary adverse health
effect from exposure to lead is
impairment (particularly in
children). Other adverse health
effects associated with lead
include sterility in males and
Mercury, or quicksilver,
was known in ancient times
as hydrargyros, hence it’s
chemical symbol ‘Hg’.
Mercury is the only metal
that is liquid at room
temperature and pressure.
Mercury is an extremely
rare element, but occurs in
deposits throughout the
world mostly as cinnabar
(or mercuric sulphide).
Like water, mercury can evaporate and
Because it is an element, mercury does
not break down into less toxic substances.
Once mercury escapes to the
environment, it circulates in and out of the
atmosphere until it ends up in the bottoms
of lakes and oceans.
Mercury can be found as the elemental
metal or in a wide variety of organic and
Depending on its chemical form, mercury
may travel long distances before it falls to
earth with precipitation or dust.
Felting and Hat-making
Thermometers and thermostats
Electric rectifiers and switches
Printer and photocopy toners.
Mercury-vapor lamps (for sterilizing water
and instead of steam in boilers
of some turbine engines.)
Amalgamation (to dissolve silver or gold to
form an amalgam, as in tooth fillings) This
process has been largely supplanted by the
cyanide process, in which gold or silver is
dissolved in solutions of sodium or potassium
Non-ferrous metal manufacturing, mining and alumina
production are the largest sources of mercury emissions in
Precious metal mining (which can emit mercury to water or
Cement manufacturing (which may emit mercury into the
Chemical manufacturing, which can emit of mercury to land
and into water.
Fossil fuel power plants may also emit mercury into the air
by burning fuels such as coal, oil, and petrol.
Our landfills and sewage also contribute to mercury being
released into our soil and water.
Small amounts of mercury can be released into the air in the
exhaust fumes of cars, buses and motorbikes.
Mercury chloride will act as a particle,
following wind patterns, and being
deposited by rain.
Elemental mercury may be a gas in the
Emissions of mercury and or mercury
compounds can produce elevated, but still
low-level concentrations in the atmosphere
around the source.
Elemental mercury can evaporate from both
soil and water into the atmosphere.
When mercury enters the environment from
emissions in the air, water or soil, it oxidises
into other compounds of mercury.
These other forms of mercury form methyl
mercury, through either chemical or
biological (bacteria) processes.
Methyl mercury builds up in the tissues of
fish and shellfish. In areas of mercury
contamination, larger and older fish tend to
have higher levels of mercury.
Eating fish or shellfish which
have been exposed to mercury.
Drinking water or eating foods
that contain traces of mercury.
Being exposed to mercury from
dental work and medical
Breathing contaminated air.
Working at, or living near,
factories where mercury is
produced or used, such as fossil
fuel plants or cement
Depending on its chemical form (elemental,
inorganic or organic) mercury is able to
cause a myriad of adverse health effects
neurotoxicity (elemental mercury, methyl-
nephrotoxicity (elemental mercury,
mercuric salts such as mercuric chloride),
teratogenicity (methyl-mercury) –
abnormalities in physiological
development, including birth defects
death (elemental mercury, methyl-mercury).
Aquatic life — the fish, shellfish and other
creatures in our rivers, lakes and oceans —
are likely to be exposed to mercury as it is
often found in water. It can make them very
sick, and may even kill them.
Mercury can build up in the tissues of fish
and shellfish and be harmful to people and
to other animals that eat them.
Once mercury is released into the
environment it will remain there for many
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