Effects of low-frequency exposure
Unlike many animals (such as birds and fish), human beings do not possess any sensory organs for electric or magnetic fields. The most we can do is perceive them indirectly. For example, some people experience a tingling sensation on their skin when standing directly beneath high-voltage power lines. Here the alternating electric field causes body hairs to vibrate, and this is perceived as a tingling sensation. While this effect may be perceived as an annoyance, it does not represent any danger to health.
Nerve and muscle stimulation
More intensive electric and magnetic fields are known to be harmful to our health, though we are not normally exposed to these in daily life. For example, extremely intensive magnetic fields over 10,000 microtesla (µT) can cause nerve and muscle cells to malfunction. Such powerful magnetic fields generate electric currents in the human organism that trigger undesirable nerve excitations and muscle contractions. And if the heart is exposed to extreme magnetic fields of more than 100,000 µT, this can cause cramping of the heart muscle – a condition that is lifethreatening. These effects on nerves and muscles are referred to as stimulation effects. They have been scientifically established and form the basis for defining international hazard thresholds. If these limits are not exceeded, no nerve or muscle cell malfunctions are triggered by low-frequency fields.
Various studies have revealed, however, that biological reactions may occur even if field strengths are well below the internationally defined thresholds. These reactions are referred to as subliminal effects. Experiments conducted on both animals and human beings have identified changes in behaviour, interference with learning capacity and impacts on the hormone system. For example, it has been found that lower than usual levels of the hormone melatonin are produced. Melatonin controls the biological day/night cycle, has a stimulating effect on the immune system and inhibits the growth of tumours. Melatonin deficiencies are associated with sleep disorders, tiredness and depressive states. Research has also identified a variety of other impacts of low-frequency fields, including influences on growth and metabolism of cells and changes in genetic material. The existence of subliminal effects is undisputed, but what we do not know is how they actually occur. Given the present-day status of knowledge, it is difficult to say whether these represent a health hazard, and if so under what circumstances.
Increased risk of leukaemia among children?
Epidemiological studies, which examine the frequency of occurrence of certain diseases among selected population groups, are a means of finding out more about any harmful effects that may be caused by non-ionising radiation. Studies of this sort have been carried out in a variety of countries since the early 1980s in order to determine whether low-frequency magnetic fields may cause or favour the development of cancer. For many years, the findings were varied and often contradictory, but as a result of more recent investigations and meta-analysis of earlier ones, researchers have meanwhile come to a uniform conclusion: the risk of contracting leukaemia is possibly twice as high among children who are exposed to magnetic fields over 0.4 µT for lengthy periods. The International Agency for Research on Cancer (IARC) also came to the same conclusion, and in 2001 it classified low-frequency magnetic fields as potentially carcinogenic for human beings. It is of the opinion that weak magnetic fields represent a possible – though not probable or proven – leukaemia risk. In Switzerland, around 60 children a year contract leukaemia. If long-term expo- sure to low-frequency magnetic fields of more than 0.4 µT really were to double the risk of children contracting leukaemia – which admittedly has not yet been definitively established – this means that about 1 new case a year would be attributable to magnetic fields, while the remaining 59 would be attributable to other causes.
The suspicion of a higher leukaemia risk is one reason to keep long-term exposure to low-frequency magnetic fields as low as possible as a precautionary measure. Insofar as electrical household appliances are the source, we ourselves are able to influence the level of exposure in our own homes. In contrast, electrical systems in our environment are subject to the provisions of the Ordinance relating to Protection from Non-Ionising Radiation, which entered into effect on 1 February 2000, and stipulates precautionary measures to reduce magnetic fields at locations occupied by people for lengthy periods of time, including residential dwellings, offices, schools, hospitals and playgrounds. At these locations, the installation limit value for all new high-voltage power lines and transformer stations at full load is 1 µT. However, long-term exposure is generally well below this level, since these systems seldom operate at full capacity. Source: Swiss Agency for the Environment Forests and Landscape. SAEFL