Further studies also suggest that high EMF levels may cause ALS. The first, which analyzed the Swedish census of 1980 against instances of neurodegenerative disorders such as Alzheimer’s disease and ALS, found that workers in the electrical or electronics industry had a 40-percent greater chance of developing ALS than those who did not work in electrical/electronic-related occupations (Epidemiology, 2003; 14: 413–9).

The Swedish study findings were supported by a later study that also found a direct correlation between exposures was more than two times greater than for those in other industries, although the risk was higher still - at four times - for Alzheimer’s disease (Epidemiology, 2003; 14: 420–6).

In yet another study, the researchers concluded that "there are relatively strong data indicating that electric utility work may be associated with an increased risk [of ALS]" (Bioelectromagnetics, 2001; suppl 5: S132–43).

Why scientists disagree
Power lines emit both electrical and magnetic fields. The electric field is related to the voltage running through the line—a typical cable handles between 275 kV (kilovolts) and 400 kV -whereas the magnetic field is dependent on the current being carried through the cable, and this can vary depending on the usage. This means that any scientist researching the impact of an EMF is faced with the immediate problem of how to measure something that can fluctuate wildly over any 24-hour period. This is why only studies that have examined EMF effects over years are able to discern any causal relationship with health problems, whereas a study that is carried out for only a few days or weeks at a time is only able to determine insignificant effects—if any at all.

Scientists who deny any association also argue that no one truly understands how EMFs can cause cancer or damage the immune system. However, as Alasdair Philips of Powerwatch, an independent consumers’ information service, says: “We still do not know the actual mechanisms by which cigarette smoking, asbestos fibre or DDT cause cancers, but we have accepted the epidemiological evidence and have introduced laws to limit or reduce human exposure.”

The distance from power lines is another issue, and sceptics have argued that people living even relatively short distances from them should not suffer any ill effects. In effect, they appear to be suggesting that illnesses being reported may just be psychosomatic—all in the head.

Professor Denis Henshaw, at Bristol University, has spent years studying this issue, and has come up with an hypothesis of ‘corona ions’. He posits that the ions emitted by high-voltage power lines are ending up as tiny charged particles of air pollution that can penetrate deeply into our lungs and bloodstream. These so-called corona ions are carried on the wind and quickly become attached to microscopic particles of air pollution, thereby electrically charging them.

Professor Henshaw believes that these pollutants can be carried several hundred metres away from power lines, which would explain why children living at greater distances - and downwind—from a line can stilldevelop leukaemia.

One task of the BioInitiative Report, prepared by 14 independent internationally based scientists in 2007, was to try to understand why there is still so much disagreement among experts, despite the fact that enough evidence has already been published to justify improvements in safety standards within the power industry.