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Chapter 12
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IntroductionMan has lived with and utilised metals since the rise of civilisation. The names for the early cultures point this out: the iron and bronze ages. Iron, copper, and tin were made into tools and weapons. But even before that, objects of gold together with mercury the only metals seen in the environment in its metal form and silver were part of human cultures. Later, from the Middle Ages, more metals were used for technical purposes: lead for tubes and window sealing, tin for cups and other items in the household. Mercury was used for its toxic properties, to cure infections. It may also have been mercury that was first noted for its adverse effects on health. Plating with gold was done with a mercury-gold mixture, and as a result, gold platers were often shortlived. An average household in the mid 19th century typically owned about 8-10 kg of metals mainly as household items and jewellery. This contrasts dramatically with today's industrial society where all items of metal in a household, from the house itself to kitchen machinery and the car, certainly includes tonnes of metals, often as complex alloys. It is clear that the flow of metals in society has enlarged enormously. After fossil fuels and macro-nutrients, metals take the third position in the large material flows in our societies. Just as the other two categories of material flows, metal flows are non-sustainable not only because of their size but because they are based on non-renewable resources and are essentially linear. This is in itself a problem which needs to be addressed Metals, generally as compounds and ions, are naturally present in the environment, and several of them are essential to biological functions. Living organisms such as plants and animals get most of the metals needed for their biological functions through water or food. Sometimes there is a lack of some essential metal, e.g. iron, and we need to add it to maintain health. The situation is thus very different from organic environmental pollutants that are entirely artificial, will eventually be broken down, and have no biological meaning, only technical or none at all. The present use of metals in society has in many cases turned out to severely damage the environment. Toxic heavy metals, most importantly mercury, lead and cadmium, constitute one major category of environ-mental threats. Most of this is man-made, though there are places where these heavy metals are naturally so abundant that they reach toxic levels, and the places themselves are dangerous for humans. Metals appear in several forms often with vastly different biological effects. Metals in organic complexes are often more toxic than their dissolved inorganic ions. Since metals are chemical elements, they never degrade, which means that they cannot be broken down or metabolised to harmless compounds, such as water and carbon dioxide, and in this way disappear. They can be washed out, be part of waste, or stored in landfills but they still remain in the environment. Several measures may contribute to make the management of metals in
society environmentally acceptable. Recycling is an important component
of this. Recycling of metals is both profitable and sustainable, and it
is possible to set up technical cycles with close to 100% recycling for
certain areas of usage. For others such as Zn, Pb, Hg, Ti, Cu, etc., in
paint or Pb in gasoline the use is dissipative. It should be noted that
the use of essential metals such as copper in many cases leads to high
concentrations that are toxic in the environment. An example is copper
in waste water sludge, released from water tubes in our homes.
Environmentally damaging use of some metals, such as use of mercury,
should be discontinued since alternatives exist. In fact, the use of
some metals, in particular mercury, lead, and cadmium, could be
entirely discontinued. The collected metals then need to be stored
forever in underground facilities, in fact corresponding to putting
them back in the mines! Authors of this chapter are: |
