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The term heavy metals often refer to metals which are toxic
in the environment.
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Most of the heavy metals are essential in small amounts for
the biological function of organisms.
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At high concentration all metals negatively influence
organisms.
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In living cells heavy metals are bound to proteins
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Iron and aluminum are the two most commonly used metals,
both are non-toxic.
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Metals are emitted to the environment from many different
point sourses, e.g. industries, waste incinerators, coal power plants,
traffic and agriculture.
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Large amounts of heavy metals are also released from the
soil due to natural weathering processes. Acidification could dramatically
enhance the processes.
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Extraction of metals produce large amounts of soild wastes
that often are major sources for heavy metal pollution.
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Almost all waters in Europe have increased levels of heavy
metals.
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Eventually heavy metals spread through the atmosphere end up
in the vegetation.
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The Minamata disaster in Japan in the mid 50's was caused by
methyl-mercury.
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The distribution pathways for mercury in the environment are
complex, including both atmospheric transport and water soluble forms.
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Mercury is concentrated in food-chains anf high levels may
occur in fish. In Sweden and Finland it is recommended not eat fish from
lakes more than once a week.
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Cadmium, lead, chromium and arsenic are other metals that
sometimes may reach unacceptable levels.
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The use of toxic metals has decreased markedly in Europe the
last decade.
