03/06/2005 - Increased Leukaemia risk living near Powerlines

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Summary

"Children who lived within 200 metres from a powerline had a 69% increased risk of contracting leukaemia compared with those who lived further than 600 metres, and those born between 200 and 600 metres had a 23% increased risk of contracting leukaemia."

"Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study"
Gerald Draper, Tim Vincent, Mary E Kroll, John Swanson

Background

Since 1979 there has been concern that the extremely low frequency electric and in particular magnetic fields may be associated with cancer. In 2001 IARC (the International Agency for Research on Cancer) classified extremely low magnetic fields as "possibly carcinogenic" on the basis of "limited" epidemiological evidence and "inadeqaute" evidence from animals.

Gerald Draper et al have looked at overhead powerlines forming the National Grid in England and Wales - that is, all 275 and 400 kV overhead lines (the highest voltages used) plus a small fraction of 132 kV lines. Subjects living within 1 km of transmission lines were identified using postcode at birth, and the shortest distance to any of the lines were able to be accurately calculated using 0.1 m grid references.

Results

For non-leukaemia cancers (central nervous system/brain tumours) there was no statistically significant connection between living near powerlines, however for leukaemias the connection was very strong. The relative risk was 1.69 for those living within 200 metres of powerlines (2.02 - i.e. a doubling, between 70 and 99 metres), and was still 1.23 between 200 and 600 metres from powerlines. Interestingly, the RR for 500-599 metres was 1.36 (36% increased risk), which was the highest ratio between 200 and 599 metres.

Explanations

The authors of the study expressed surprise that the increased risk stretches so far from the lines, as the magnetic fields from powerlines are below other household sources further than 200 metres away. Despite this, they propose that exposure to magnetic fields is the most obvious and logical cause of the increased leukaemias. However, they also state that they "have no satisfactory explanation for our results in terms of causation by magnetic fields, and the findings are not supported by convincing laboratory data or any accepted biological mechanism".

However, Powerwatch believe that the effect closer than 200 metres could well be due to magnetic fields, though it is interesting noting that 200 metres is beyond the point at which magnetic fields have dropped well below 400 nT. We support another theory that would provide the evidence for the increase up to 600 metres and potentially slightly beyond:

Corona Ions

We would agree that it seems highly unlikely for magnetic fields to be responsible for a 36% increase in leukaemias between 500 and 599 metres away from powerlines. However, there is a theory from Bristol University suggesting corona ion / charged toxic aerosol effects which would fit this distance and also offer a plausible mechanism by which the development of leukaemia could be initiated.

These corona ions are created principally by the high electric fields surrounding the powerlines themselves. It is well known that these ionise the air, which causes "avalanching" of charge and can mean that the total number of ions involved in corona loss can exceed the loss current. In the general case, most of these corona ions recombine with the powerline, however, some of these escape (for example due to wind) and quickly nucleate or attach to ultrafine aerosols. These aerosols are then dispersed by normal atmospheric processes such as the wind, and will eventually attach to larger aerosols. Cohen et al. (1998, Health Physics, 74(5), 554-560) have demonstrated a five- to six-fold increase in lung deposition when the aerosols were charged compared with uncharged.

This is extremely important, as it means that harmful isotopes of heavy metals such as lead, polonium and cadmium in the atmosphere have a five to six times greater chance of being deposited in your lungs, potentially increasing the harmful effects of air pollution by up to 500%. According to Professor Henshaw of Bristol University the effects of corona ions are unlikely to be present at all within 150 metres of powerlines, but could quite easily be the major factor in the increase in leukaemia seen greater than 200 metres away.

This is of great importance because Bristol University have found similar levels of corona ions from 132 kV lines, which are not only far more common, but also are much more prevalent amongst residential housing than the larger 275 and 400 kV powerlines looked at within the study. As such, if we are to take Draper et al.'s figure of 5 in 400 cases of leukaemia per year being attributed to powerlines, taking into account 132 kV lines could proportionally increase this figure to as high as 50 in 400 cases, which is 12.5% (1 in 8) of all cases per year in the country!

This certainly challenges the flawed conclusions in the news just over a month ago where powerlines had effectively been written off as insignificant by Dr. David Grant, Scientific Director of the of the Leukaemia Research Fund, supported by Professor Eve Roman and Professor Mel Greaves, and really makes further investigation into powerlines and associated adverse health effects an absolute necessity for the future safety of the British population.

In the meantime Powerwatch calls for an immediate ban on the building of new homes, schools and nurseries within 150 metres of high-voltage overhead powerlines. We also call for an extension of this study to cover children living close to 132 kV powerlines.

For a deeper look at the science behind this interesting work, please refer to the Bristol website.