Key events and papers on the (now well established) association between exposure between powerline magnetic fields and childhood leukaemia, in the light of recent developments, are:
1. Feychting and Ahlbom [Amer. J Epidemiology 138 (7), 467-481, 1993] established an association between magnetic field exposure above 0.2microTesla and childhood leukaemia, which was accepted by NRPB as a well conducted study. The actual cases (there were just 7) were all above 0.3microTesla so the effective threshold of association was very uncertain and could well be above that level, though from then on it was often discussed as though it was 0.2microTesla.
2. The UKCCS published results [Lancet 354, 1925-1931, 1999] showing no childhood cancer association with magnetic field exposure up to 0.2microTesla, but with insufficient data to draw a conclusion at higher exposures. An editorial comment in the same issue of the Lancet (page 1918) recognised the limitations and the lack of any essentially new conclusions from the paper.
3. Ahlbom et al [Br J Cancer, 83, 692-698, 2000] published a meta- analysis confirming the association of childhood leukaemia and magnetic field association above 0.4microTesla and the lack of it below that level.
4. The UKCCS [Br J Cancer, 83(11), 1573-1580, 2000] published its investigation into childhood cancer and residential proximity to powerlines (as distinct from magnetic field exposure). I gathered this was in response to the submissions made by Prof Henshaw when the original UKCCS results were published. Again no association was found, but the analysis is very limited indeed: very few cases or controls lived within 50 metres of high voltage lines, although for 110kV lines there were rather more, but few living further away. The comparison of distance to calculate odds ratios is very unsatisfactory, comparing only a unit increase in the "exposure metric", e.g. comparing 20 metres with 25 metres, which is absurd. We really need to compare, say, under 25 metres with over 200 metres, though the data in this study are insufficient to do this. In my view this study does not support any sensible conclusion on association or not, and the metric and comparisons chosen were never likely to bear results.
There are further analyses still to come from UKCCS, including the relationship with electric field exposure.
5. The NRPB issued a statement 21 November 2000, recognising the Ahlbom paper (item 3 above) and saying "For magnetic field levels of 0.4microTesla or more, the leukaemia risk was estimated to be doubled; this finding is unlikely to be due to random variability, but the authors suggest this may be accounted for in part by selection bias". The NRPB statement also says "for the overwhelming majority of children living in homes with magnetic field levels below 0.4microTesla - estimated to be 99.6% of children in the UKCCS - the data were consistent with no increased risk". That applies to the majority of children who do not live near powerlines, so it is a rather empty assurance as they would not expect to be at risk from such magnetic fields because they aren't exposed to them.
Incidentally these issues were given a good airing at Hearings in Donegal last week, where I gave evidence along with Roger Coghill and others, though my evidence was mainly to challenge "need" for that line. The electricity board (ESB) brought over an experienced highly ranked witness, Dr William Bailey, from USA, who gave the industry view, selecting quotes from international reviews to support his case. He did however agree with me in cross-examination that, on whether power- installation EMFs are causes of harm to human health, (a) it is not proven; (b) it is possible; (c) there is some suggestive evidence; (d) there is insufficient evidence to set a formal precise exposure limit; (e) a response of further research is justified. When it came to a final question, (f) "would you agree that, given a choice of creating a new exposure or not, other things being equal, choosing avoidance of exposure would be reasonable", he held back and would not answer directly.
-- Mike O'Carroll