First, children living near power lines were believed to be at risk for leukaemia. Then, mobile phones were going to fry our brains. Now, should we worry about Wi-Fi hotzones?

Prompted by citizen concerns , the Toronto Board of Health is conducting a study of the potential health risks posed by plans to blanket the downtown core with Wi-Fi access points.

Also in Canada, which seems to be the nation most terriried by Wi-Fi, Lakehead University in Ontario has banned the use of Wi-Fi on campus in fear of such a link.

All manner of infrastructure and consumer devices – power lines, radio towers, Wi-Fi routers, mobile phones, radio and television, and so on – emit electromagnetic radiation at different frequencies, with varying effects on biological systems.

The electromagnetic spectrum is divided into two major categories, ionizing and non-ionizing radiation.

High-frequency radiation with shorter waves at the ionizing end of the spectrum, such as X-rays and gamma rays, has undisputed detrimental effects on human health. At the borderline between ionizing and non-ionizing is ultraviolet radiation, emitted by the sun, which also has a clear link to skin cancer.

Health effects

Controversy rages at the non-ionizing, lower-frequency end of the spectrum. At the lowest end are electromagnetic fields (EMF) such as those created by power lines. The longer the wave, the fewer health effects.

Radio waves, which are used in mobile phones, Wi-Fi, radio, television and other consumer devices, operate at a higher frequency than power lines. Microwaves, which are used in radar and ovens, are a sub-set of radio waves, and have an even higher frequency.

Research conducted in Switzerland provides some fair evidence of a link between RF emissions from radio towers and sleep disturbances. So maybe it's actually the baby monitor keeping junior up all night…

Mobile phone towers operate at 10,000 times the power of our Wi-Fi units, and FM radio towers are 100,000 times."