It was financed by the U.S. Congress, the electrical industry in the U.S. and the National Institute of Environmental Health Sciences. In a separate Canadian study published today, researchers from the University of Toronto and Toronto Hospital for Sick Children appear to confirm the risk. The researchers measured the magnetic fields in the homes of 201 children diagnosed with leukaemia in the Toronto area between 1985 and 1993, comparing them with those of 406 healthy children. When family relocations, power use and the child's medical history were taken into account, children exposed to high magnetic fields were 4.5 times more likely to develop leukaemia. Dr. Green's study is reported in two separate papers in the International Journal of Cancer and the journal Cancer Causes and Control.
Magnetic fields are invisible lines of force that surround all electrical devices and wiring.
But homes located near heavy transmission lines and utility transformers, or which have poorly grounded wiring, often have a much higher magnetic field. The Canadian study was funded in part by the Ontario Hydro Services Company and the Canadian Electricity Association. Some studies quoted in the U.S. report to Congress suggest a dramatic increase in leukaemia risk for exposures between 4 and 5 mG, a strength that is not unusual in urban areas across North America. Until a biological reason for the association can be found, much skepticism about the statistical risk will remain. Dr. Mary McBride, an epidemiologist, suggested that frequent moves may expose children to different patterns of viral infections, which may be linked to leukaemia.