Eirgrid's plan for essential upgrading of the national electricity power grid is attracting stiff opposition from communities living near the proposed new works, mainly on the grounds that the power lines pose a health hazard. Extensive scientific investigations have failed to find a convincing link between exposure to electromagnetic radiation from power lines and cancer, but a weak correlation with childhood leukaemia has been reported since 1979. The most recent review of studies into the possible health effects of exposure to electric and magnetic fields (EMF) from power lines was published by the EU just last week.

Electrical power is transported over long distances along overhead high-voltage transmission lines, and these lines generate EMF, as also happens when electricity passes through conductors in domestic electric wiring and electric appliances. It is relatively easy to shield against electric fields, but more difficult to shield against magnetic fields. There is little evidence that these electric fields impact significantly on health, and the great majority of reports on public-health effects deal with magnetic fields.

The unit of magnetic field is the Tesla (T). A micro T is one millionth of a T. Magnetic field strength decreases rapidly with distance from the source. A magnetic field strength of 11.2 micro T will register directly underneath a 400 kilovolt transmission power line, but 40m from the centre line this will drop off to one micro T. To put this in context, the magnetic field strength one metre from an operating electric cooker can range from 0.2 micro T to three micro T.

We can have confidence that EMF is not a significant cause of overall cancer. An impressive study was published by JD Jackson in Proceedings of the National Academy of Sciences (1992). Installation of electrical power generation and consumption of electricity increased exponentially in the US throughout the 20th century, and exposure of the general public to EMF increased correspondingly. If exposure to EMF is a significant factor in cancer, this would be reflected in cancer statistics. However, the age-adjusted death rates from all cancers increased very little from 1900 to 1990 – 0.8 deaths per 1,000 in 1900 to 1.3 deaths per 1,000 in1970, after which the death rate remained constant. Most of the increase in the early years is attributable to more complete reporting of cause of death.

An exception
Childhood leukaemia is an exception to the pattern noted above. A link to EMF was first reported in 1979. Later studies in the 1980s and 1990s produced conflicting results, but were of low statistical power. Ablom and others combined several studies done up to the late 1990s to create large, statistically significant samples. They found a tendency towards a very small increased risk for childhood leukaemia in areas close to power lines for time-weighted average exposures greater than 0.4 micro T ( Environmental Health Perspectives , 2001). The recent EU report confirms this finding. Such exposures are rarely encountered by the public. If real, this extra risk would correspond to one additional case of childhood leukaemia in Ireland every four years.

There is no credible biophysical mechanism to explain how exposure to low-level magnetic fields could cause leukaemia. Also, studies on people occupationally exposed to EMF from power lines and other sources, who receive higher exposure than the public, have not shown raised risks of leukaemia.

The World Health Organisation, the International Agency for Research on Cancer, the International Commission on Non-ionising Radiation Protection and the recent EU report have concluded that there are no substantial health issues related to magnetic fields at levels encountered by the public – and any link to childhood leukaemia is too weak to be causal. Occasionally reported links to Alzheimer's, miscarriage, suicide, depression, Parkinson's and cardiovascular diseases have not been confirmed by recent, more thorough investigations.

Magnetic field strength at ground level from underground cables falls off much faster with distance than it does with overhead cables, and new high-voltage cables can be buried in order to reduce public exposure. However, burying cables costs several times more than overhead cabling. It might make more sense to spend this money to reduce bigger risks – for instance, about six children aged under five are accidentally drowned annually in Ireland.

William Reville is an emeritus professor of biochemistry at UCC, understandingscience.ucc.ie