Twenty years of work worldwide, involving 12,000 scientific studies costing £300 million, have so far failed to establish definitively that illness can be caused by living near overhead power lines. The latest research from Britain has also yet to make this connection.
However, people want assurances that no risk will be discovered in the future, and that life under the pylons will never result in disease. No scientist worth his or her salt will make such a promise, however, and no guarantee can be given.
Scientific research is a strange business, with every fact and bit of knowledge assumed to be only conditionally true until it is proven otherwise. Absolute promises are dangerous to make.
For this reason scientists constantly scrutinise one another's work, testing and retesting claims made by others. An important part of this process involves publication in journals in which research is subjected to rigorous "peer review". This is intended to ensure that the work is original, was properly done, and that strict controls were placed on the collection and interpretation of the experimental data.
The latest of many scares relating to power lines arose this week from work done by two researchers from the University of Bristol. Their studies claim to show both how the power lines might cause a hazard and that the hazard causes illness.
The hazard was defined by Prof Denis Henshaw in two research papers published in the International Journal of Radiation Biology last December, so these are not strictly new. In these papers he argues that power lines continuously throw off ions, electrically charged particles produced by sparking.
The ions in turn attach to pollution from cars and industry, giving particles of the pollution an electrical charge. His theory, based on research by others, holds that these charged pollutants will be much more likely to stick to the lungs when breathed in, increasing the amount and impact of the pollution.
The claims about actual illness relate to an as yet unpublished epidemiological study carried out by Dr Alan Preece of the Bristol Medical School. Although the study has yet to be offered for scientific scrutiny, he released preliminary findings while attending a conference early last summer in Munich.
He claimed at that time that an analysis of cancer incidence suggested there was an estimated 29 per cent increased risk of illness for those living within 400 metres of these lines. In particular, he said, the risk was for those "downwind" of the lines, on the basis that the wind would blow electrically charged pollutants towards them.
No further discussion of this work was available yesterday from either the researcher or the university, according to Ms Joanne Fryer for the University of Bristol, because the work had yet to be published.
His claims were available yesterday, however, on the Website of Powerwatch, which campaigns about the alleged risks associated with power lines (http:// www.powerwatch.org.uk). Dr Preece was also preparing to discuss the work last night on BBC Radio 4's Costing the Earth programme.
Mr John Gartland, the ESB's specialist on the effects of both electrical and magnetic fields on human health, was predictably dismissive of both of these research claims. "From our perspective it is old news," he said yesterday.
The company continually reviewed all research relating to power line safety, he said, and acted on the basis of what the science was saying. "One of the things for me is that the written science word is quite a precise tool as opposed to what is said in a press release or on the radio."
He was unhappy, however, about the worry that reports of risks might cause in the general public. "We are very concerned that people would be unduly concerned," he said, adding that repeated studies had shown the risks to be either not there at all or so small as to be of no consequence.
An Irish specialist, Dr Jim McLaughlin, the head of the radon research group at University College Dublin, has studied how this natural pollutant is influenced by the lines.
He and colleagues measured radon accumulation in Co Meath under the 440,000 volt transmission line that runs from Moneypoint to Dublin. Measurements were taken up to several hundred metres either side of the line, both when it was switched off for maintenance and while fully energised.
"We couldn't see any difference in the exposure between when the line was on or off. We could detect no measurable effect on radon accumulation," he said yesterday. "The power line didn't have any detectable effect."