In what's believed to be a first in the city, Toronto Public Health tested 31 schools this spring that are next to hydro corridors.
The tests found that two Monsignor John Corrigan elementary in Etobicoke, and JS Woodsworth senior public school in Scarborough had the highest readings.
The Etobicoke Catholic school had a snapshot reading of 69.9 milligauss (mG) and the one in Scarborough showed 29 mG. According to public health, background levels of electromagnetic fields (EMF) in urban areas are usually less than 1 mG.
Both tests were done outside, on school property. Further testing is scheduled for inside.
A test at Tamarisk Park, near the Etobicoke school, had readings of between 33 and 81 mG.
Though Canada follows international guidelines permitting short-term exposure at no more than 833 mG, studies have shown the risk of leukemia in children increases if they're exposed to average levels, year-round, above 3 or 4 mG.
Ronald Macfarlane, a supervisor in the city's environmental health assessment section, said short-term exposure to high EMF levels won't significantly raise a person's yearly average level. There's no need for parents to be alarmed, he said.
"We're encouraging schools to take practical measures to not unduly increase exposure to EMF," Macfarlane said.
Still, public health is recommending the schools come up with a "management plan" so children at the two schools aren't exposed too long to areas with high readings, Macfarlane said.
The Catholic board will notify parents in a letter.
The public board will wait for the results from indoor testing, and if concerns remain after those results are in, a meeting will be scheduled with parents.
Electric and magnetic fields are invisible lines of force, part of the spectrum of electromagnetic radiation.
Aside from studying EMF levels beside hydro corridors, public health has published an extensive new report on EMF exposure in general. In it, Dr. David McKeown, the city's medical officer of health, calls for housing developments, schools and recreational facilities beside these corridors to develop "management plans."
The goal is to minimize yearly average exposure, especially for children. Plans can be as simple as locating areas of high child activity away from EMF hot spots.