The term heavy metal refers to any metallic
chemical element that has a relatively high density
and is toxic or poisonous at low concentrations.
Examples of heavy metals include mercury (Hg), cadmium
(Cd), arsenic (As), chromium (Cr), thallium (Tl), and
lead (Pb).
Heavy metals are
natural components of the Earth's crust. They cannot
be degraded or destroyed. To a small extent they enter
our bodies via food, drinking water and air. As trace
elements, some heavy metals (e.g. copper, selenium,
zinc) are essential to maintain the metabolism of the
human body. However, at higher concentrations they can
lead to poisoning. Heavy metal poisoning could result,
for instance, from drinking-water contamination (e.g.
lead pipes), high ambient air concentrations near
emission sources, or intake via the food chain.
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Heavy metals are
dangerous because they tend to bioaccumulate.
Bioaccumulation means an increase in the concentration
of a chemical in a biological organism over time,
compared to the chemical's concentration in the
environment. Compounds accumulate in living things any
time they are taken up and stored faster than they are
broken down (metabolized) or excreted.
How do
heavy metals affect our health?
Several metals such as
lead, cadmium, cobalt, nickel and alkyl mercury
compounds have an effect on haematopoiesis and can lead
to blood disorders. The liver, the kidneys, the
circulatory system and the nervous system may also be
affected. Beside their toxic effects, some heavy metals
(arsenic, hexavalent chromium and nickel) also have
potential carcinogenic effects.
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