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Mobile telephony has been the latest technology to join the long list of sources of electromagnetic pollution which technological progress has inflicted on our world. If you want to know where the rest of the list comes from, take a look around your house and check out the amazing number of cables and electrical devices that are all around us.

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Wherever there is a flow of electrons through conductive material an electromagnetic field is produced, that is, a zone in which there are electric and magnetic forces. We are naturally exposed to the action of electromagnetic fields. On Earth, for example, there is a natural field of electricity caused by the difference in tension between the atmosphere and the ground, which as we all know is much more intense during storms. And the movement of magnetic material within the Earth's crust creates a magnetic field which makes our planet act like a gigantic magnet, which is responsible for, among other things, the fact that the needle of a compass always points north. Infrared and ultraviolet rays emitted by the Sun also have a natural origin as do X and gamma rays which come from space. Even the light we see by is no more than an electromagnetic wave.

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However in the last century man has put an enormous quantity of new artificial sources of electromagnetic emissions onto this planet, which has upset the natural electromagnetic atmosphere, increasing its density a thousand million times over. We still do not know exactly what the real consequences of these emissions are, though in recent decades thousands of studies throughout the world have warned of their hazard. The effects of electromagnetic radiation on living organisms are different depending, among other things, on the type of waves, the distance from the source, and the period of exposure.

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The main difference between the different electromagnetic waves is their frequency - that is, the quantity of waves which pass through space every second - which determines the energy they transmit: the higher the frequency the greater the energy. The frequency of electromagnetic fields is measured in hertz (Hz) and their intensity in microtesla (�T). The strongest radiations are called ionising because they have enough energy to strip electrons from their atoms; this converts them into ions and provokes chemical reactions which can affect some complex molecules of great importance to human life such as DNA. Among these very high frequency radiations are X-rays, ultraviolet or gamma rays, which have all been known to be highly dangerous for a long time now.

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Other waves are known as non ionising. In the past these were not considered to be dangerous but in recent decades the results of a great deal of research have been published which show certain ill effects, especially after prolonged exposure. These non-ionising radiations can also be divided into groups, according to frequency. Among producers of extremely low frequencies (50 Hz) are high tension power lines, transformers and the electrical appliances we use in our daily lives. Radio and television installations produce higher frequency radiations, while mobile telephones and the antennae which give coverage to them produce frequencies which are higher still (between 850 and 950 MHz). In an even higher scale of non-ionising radiations are those emitted by microwave ovens or devices which work with infrared.
Other devices, like the computer, are not dangerous due to the strength of their radiations but because of the time we spend glued to them every day .

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DID YOU KNOW...?
� The strength of the Earth�s magnetic field depends on exactly where you are on the globe. In the case of Spain it is 40 microtesla. The radiation we receive from the Sun is 50 nanotesla (0.05 microtesla). The radiation of a mobile telephone is 3 million times greater than natural radiation.
� On 28 September this year the Government passed a Royal Decree regulating exposure limits to radio-electric emissions from mobile telephony antennae. This legislation set minimum safety distances for the installation of such equipment at 6 metres from a home and 54 metres from a school or hospital. In August the European Union had for the first time established an obligatory limit for radiation emitted by mobile telephones so as "not to expose users to an excessive electromagnetic radiation". Both measures are based on a UE recommendation dating from July 1999.
� Electromagnetic waves do have a good side too. Medical science uses them for the regeneration of tissue and treatment of some types of cancer, among many other applications.