“New research on high voltage powerlines and public health: possible links to leukaemia.” – press release, University of Bristol, UK, 1 December.
“Major study finds no link between overhead power cables and childhood cancer.” – press release , UK Childhood Cancer Study, 3 December
The debate on powerline health effects continues. The University of Bristol research, reported in the International Journal of Radiation Biology, suggests that power-frequency electromagnetic fields might concentrate airborne pollutants and account for the association – albeit weak – that has been reported between powerlines and childhood leukaemia. In May, for example, the US National Institute of Environmental Health Sciences (NIEHS) presented a report to Congress which stated that EMF exposure “cannot be recognised as entirely safe because of weak scientific evidence that exposure may pose a leukaemia hazard” and recommended that the US power industry “continue its current practice of siting powerlines to reduce exposures”
But the association certainly is weak and interestingly the UK Electricity Association cites this same NIEHS report as “further confirmation that the weight of leading world scientific opinion now believes that these fields are unlikely to cause ill-health.”
The Bristol team, led by Professor Denis Henshaw, is nevertheless firmly convinced there is an association and has set itself the task of looking for the causal mechanism. The team has made over 2000 experimental observations at a number of sites and found increased deposition rates on plastic surfaces near powerlines. They suggest that similarly increased deposition rates of pollutants might apply to people near powerlines, leading to health effects. They also propose that the effects are not confined to the area immediately under powerlines. Their hypothesis is that dirt on powerlines causes them to emit corona ions, which can electrically charge pollutant aerosol particles, making them more readily lodged in the lung if inhaled. “While the risk of leukaemia is small,” said Professor Henshaw, “it may be an avoidable risk. It confirms that the American government’s policy of not siting houses close to powerlines is well founded.”
There is however considerable scepticism about Professor Henshaw’s claim to have established a causal link between powerlines and health effects, and not just in the electricity industry, where you would expect to find such scepticism.
The UK’s independent radiation safety body, the National Radiological Protection Board (NRPB), says it does not dispute “the physical mechanism of increased deposition of charged particles on surfaces near to powerlines” and notes that such effects have been known for over 16 years. However, it has great doubts that the findings of the Bristol team can be “extrapololated to real health effects.”
The NRPB finds much more convincing the work of the UK Childhood Cancer Study, the largest epidemiological project on childhood cancer ever undertaken. Its first paper, on power frequency magnetic fields and the risk of childhood cancer has just been published (The Lancet, 4 December) and will be followed by separate reports on the effects of electric fields and other possible causes of childhood cancer.
Reassuringly, the study finds “no evidence that exposure to magnetic fields associated with the electricity supply in the UK increases risks for childhood leukaemia, cancers of the central nervous system or any other childhood cancer.”
The size, scope and rigour of the study is such that its eminent chairman, Sir Richard Doll – who is credited with finding the link between smoking and lung cancer – even goes so far as to say that he believes there is “now no justification for further epidemiological studies on EMF and childhood cancer in Britain.”
But other researchers are less sure, as a commentary by M Repacholi and A Ahlbom of WHO, published alongside the UKCCS paper, makes clear. The World Health Organization, which itself has an international project on EMF health effects, accepts that the UKCCS is “very large and well conducted”, but says “it is not the ‘definitive’ study many scientists have been hoping for.”
One reason is that the UKCCS exposure assessment uses time weighted averages for the magnetic fields but does not take account of transients, ie rapid changes in the fields, which may exacerbate the effects. Another concern is that the exposures considered in the UKCCS are relatively low, with only 2.3 per cent of children exposed to over 0.2µT. While this is in line with German experience, the corresponding figures for the USA and Canada appear to be roughly 11 per cent and 15 per cent, respectively (reflecting in part the difference in line voltage between North America (110 V) and Europe (220 V), which means for a given power twice as much current is needed at the North American voltage). The UKCCS does not have much to say about exposures over 0.2 µT because such levels appear to be unusual in the UK.
The UKCSS work is undoubtedly of major significance, but it is by no means the last word on powerline health effects. However, studies currently underway in Japan, Germany and Italy, when coupled with the UKCSS findings, should take us much closer to a resolution of the issue in the not too distant future.
