High voltage power lines and risk of cancer
BMJ 1997; 314 doi: https://doi.org/10.1136/bmj.314.7076.305a (Published 25 January 1997) Cite this as: BMJ 1997;314:305Conclusions are unjustified
- M J O'Carroll, Emeritus professora
- a University of Sunderland, Sunderland SR2 7EE
- b Department of Public Health, PO Box 41, FIN-00014 University of Helsinki, Finland
- c Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, FIN-00170 Helsinki, Finland
- d Department of Public Health, University of Turku, FIN-20520 Turku, Finland
Editor–Pia K Verkasalo's study of the magnetic fields of high voltage power lines and the risk of cancer in Finnish adults goes some way to assuring adults who live about 100 m from high voltage power lines that they may not thereby be at an increased risk of cancer in general.1 In their analysis, however, the authors did not isolate the more highly exposed residents, such as those living within 25 m of high voltage power lines. Possible effects on them are lost by dilution in the much wider pool of the authors' highest category of exposure.
The authors measured cumulative exposure over 20 years in µT years. There were five categories of exposure, ranging from<0.2 µT years in the lowest category to >2 µT years in the highest category. The mean value in the highest category was 5.04 µT years.
Typical ambient household exposures in Britain, independent of power lines, are in the range 0.01-0.2 T,2 with 0.05 T being a representative value.3 Twenty year exposure to typical ambient fields would give 1.0 µT years, which would fall in the authors' second highest category. The highest category had on average only five times ambient exposure. On the other hand, exposure close to power lines is much higher. Table 1 shows magnetic flux densities (typically at 1 m above ground) according to the horizontal distance from the centre of the power line. The figures from the Central Electricity Generating Board in Britain are taken from an internal report. In general, the fall off varies from roughly the inverse square to the inverse cube of the distance, depending on the phasing of the current.
The 20 year exposure of residents living 100 m from high voltage power lines may typically be around the mean in Verkasalo and colleagues' highest category, at 5 µT years. It would be more interesting to examine the category with a mean exposure of 50 µT years, which would better represent the higher exposure of residents within 20 m of power lines. As it is, the claim in the key message that “the results of the present study suggest strongly that typical residential magnetic fields generated by high voltage power lines are not related to cancer in adults” is unjustified.
References
Authors' reply
- Pia Verkasalo, Researcherb,
- Jaakko Kaprio, Senior scientistb,
- Kauko Heikkilä, Systems analystb,
- Eero Pukkala, Researcherc,
- Markku Koskenvuo, Professord
- a University of Sunderland, Sunderland SR2 7EE
- b Department of Public Health, PO Box 41, FIN-00014 University of Helsinki, Finland
- c Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, FIN-00170 Helsinki, Finland
- d Department of Public Health, University of Turku, FIN-20520 Turku, Finland
Editor–We agree with M J O'Carroll that, from the scientific point of view, it would be more interesting to examine residents living, for example, within 20 m of power lines or otherwise exposed to higher magnetic fields. This, however, was not possible, as can be deduced from previously published distributions of buildings and people by proximity to power lines and by calculated annual average magnetic fields1 and also from the tables in our paper. For instance, in 1989 the total number of Finnish people living within 20 m of high voltage power lines was 2100. Of them, 350 were exposed to a calculated annual average magnetic field of 0.3-0.49 µT, 550 to a field of 0.5-0.99 µT, and 350 to a field of ≥1.00 µT. The highest cut off point for cumulative exposure was set at 2.0 µT years because one would otherwise expect to have very few cases.
These distributions also give some indication of what can and what cannot be regarded as a “typical residential magnetic field generated by high voltage power lines” (magnetic fields of the order of ≥5 µT are not typical). It is, however, clear that the results of our study “cannot exclude the possibility of an increase in risk at higher magnetic field levels” (as we said in one of our key messages).
References
- 1.↵
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