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Power lines and cancer
= Current concerns
Mar 8th 2001
From The Economist print edition
BACK in the= 18th century, magnetism was all the rage for treating a wide variety of = ailments. Today, however, the rage is mainly confined to those who feel t= hat electromagnetic fields (EMF)—particula= rly those emitted by overhead power lines—are the cause of their dr= ead diseases.
For the pas= t 20 years, scientists have been investigating a possible link between ra= re ailments, such as childhood leukaemia and certain adult cancers, and e= xposure to EMF, either through living at close q= uarters to electricity lines or working alongside them at electrical util= ities. Several large studies carried out in Scandinavia, America, Canada = and Britain have, on the whole, concluded that there is little risk of ca= ncer associated with EMF exposure. But shortcomi= ngs in some of their methods, and a lack of agreement between their resul= ts, has kept the debate electrified.
This week, = a group of British researchers advising the government’s National R= adiological Protection Board weighed in with their assessment of the dang= ers of EMF. Having trawled through hundreds of e= pidemiological and laboratory studies published on the subject and taken = into account their various flaws and biases, the advisory group agreed wi= th the prevailing view that the association between EMF= exposure and human cancer is weak. Its members found little convi= ncing evidence of a connection between the sort of heavy-duty occupationa= l exposure which, say, an engineer at an electrical substation might expe= rience and either adult leukaemia or brain cancer. The advisory group did= note, however, that prolonged residential exposure to relatively strong = magnetic fields of greater than 0.4 microteslas is associated with a doub= ling of the risk of a child developing leukaemia.
This might = sound alarming on the surface, but is less frightening in the detail. The= British study estimates that around 300,000 people (0.5% of the country&= #8217;s population) are exposed to magnetic fields with a strength of 0.4= microteslas or more. (Background field-strengths in most British homes r= ange from a fortieth to a half of this level, with occasional brief surge= s due to electrical appliances such as shavers and blenders.) So quite a = few British children fall into this risk category. But childhood leukaemi= a is an uncommon ailment in the first place, with 500 cases reported each= year in Britain. The researchers estimate that exposure to strong magnet= ic fields might be associated with an additional two cases of leukaemia a= year.
But Anthony= Swerdlow, an epidemiologist at the Institute for Cancer Research in Lond= on and a member of the advisory group, is quick to point out that even if= EMF is associated with childhood leukaemia, tha= t does not mean that it causes it. Laboratory testing, using isolated cel= ls or experimental animals, has failed to show much of an effect on biolo= gical processes by the sort of EMF that might co= me from electrical supply lines. And since it is known that EMF does not directly alter DNA, one= of the key steps in causing cancer, researchers are hard-pressed to come= up with a plausible mechanism as to how such fields might cause trouble.=
It is possi= ble that EMF acts in conjunction with another ag= ent which causes cancer, but this is hard to pin down in population-based= studies since there are countless suspects lurking in the real world. It= might be easier to expose such a carcinogenic conspiracy in the laborato= ry, but there are few adequate animal models of childhood leukaemia yet a= vailable to test the hypothesis.
In any case= , this latest report on EMF and cancer is unlike= ly to be the final word on the subject. The researchers themselves call f= or additional studies on cells and animals. And while there are too few p= eople in the high-exposure category in Britain to do further useful epide= miological studies, the group does recommend more population-based work, = using the best techniques available, in other countries with higher expos= ures. Researchers also want to address the curious finding that four-fift= hs of the children in the high-EMF exposure cate= gory in Britain do not live near overhead power lines. The source of thei= r EMF exposure, whether from household wiring or= other causes, will need further investigation.
The bottom = line, as Dr Swerdlow points out, is that exposure to EM= F is linked to a modestly elevated risk of a very rare disease in = a small section of the population. Unfortunately, this is unlikely to qui= eten public fears of widespread danger from electricity lines. Childhood = leukaemia is a cruel disease, and parents are naturally keen to find the = cause. Blaming menacing electrical pylons and invisible, malign radiation= is understandably easier than accepting the fact that science does not y= et know what triggers this affliction in some children. In an age which e= xpects iron-clad scientific solutions, living with uncertainty, however s= mall the danger, is no easy thing.
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