Risk of cancer and exposure to power linesBMJ 1994; 308 doi: http://dx.doi.org/10.1136/bmj.308.6937.1162a (Published 30 April 1994) Cite this as: BMJ 1994;308:1162
Still no answers
EDITOR,--The Danish1 and Finnish2 studies suffered from similar serious shortcomings to those which have plagued much of the published research on the possible adverse health effects of power-frequency magnetic fields.
Firstly, as part of their objective both studies only considered high voltage ( > 50 kV and > 110 kV) power lines. The effect of this is to greatly reduce the likelihood of any associations being found, because many cases will occur in equally high magnetic fields due to other sources, and the study will not have recorded these as being in a high field. It has been repeatedly shown that magnetic fields from 33 kV down to 415 V distribution lines often give rise to fields in excess of 0.25 μT, and I have recorded 1.5 μT in bedrooms due to 33 kV lines. The effect of this objective alone is to make the results fairly worthless in determining whether there is any link between power-frequency magnetic fields and cancers.
In the Finnish study the authors calculated fields down to 0.01 μT (10 nanotesia). The average magnetic field in British houses, as a result of wiring, is in the order of 0.03-0.06 μT, and street wiring and low voltage distribution wiring often raises this to well in excess of 0.1 μT. I would be surprised if Finnish magnetic fields were significantly lower, and this would completely mask the analysis of their calculated fields.
Secondly, the fields were calculated on the basis of the average flow over a full calendar year. The magnetic field at a distance from a power line is critically dependent on the actual phase current values and power factors, and small changes in current balance cause large changes in the calculated field. Yearly average current flows will not provide this essential level of detail, and so the calculated values are likely to have margins of error of at least 100% due to this fact alone.
Thirdly, if, as has been suggested, the critical exposure period is night time, when people are resting, then the exposure during winter months will be many times that during the summer months. In the United Kingdom, especially in rural areas, overnight field levels can be three times the day values during winter months due to loads from off-peak storage heating.
Finally, most of the possible mechanisms which have been suggested and shown in cellular experiments as being responsible for biological effects of electromagnetic fields are based on resonance phenomena, which involve both the alternating power-frequency field and the earth's local geomagnetic field. None of the epidemiological studies published to date have collected this essential extra data.