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Japan Maritime Self-Defence Force (JMSDF) personnel, wearing protective suits, board a tugboat from the JMSDF destroyer Sawayuki, near Tokyo Electric Power Co.'s Fukushima Daiichi Nuclear Power Plant in Fukushima Prefecture, northeastern Japan, in this photo taken March 31 and released by Japan's Defence Ministry April 1, 2011. Picture taken March 31, 2011.
Photograph by: REUTERS/Japan Maritime Self-Defence Force/Handout
OTTAWA — Radiation monitors in Ontario, New Brunswick and British Columbia have detected minute traces of radioactive iodine suspected to be from Japan's stricken Fukushima nuclear plant.
The Canadian Nuclear Safety Commission characterizes the quantities of Iodine-131 (I-131) as infinitesimal and stresses there are no health hazards to Canadians.
Bruce Power, operator of the Bruce nuclear generating station on the shores of Lake Huron northwest of Toronto, recently reported traces of airborne I-131 in a small number of monitoring samples.
"It has been concluded that this I-131 is likely due to the result of emissions of I-131 from the Fukushima plant in Japan," the commission said in a news release.
I-131 is produced by the fission of uranium atoms in nuclear reactors and by plutonium (or uranium) in the detonation of nuclear weapons.
Analysis of the Bruce Power samples, taken in mid- to late-March, indicate the effective dose to a person would be approximately 0.03 of a microsievert if a person breathed in this concentration of air, and was exposed externally to this air for an entire month, said the commission. And that does not take into account the radioactive decay that would occur during that time. I-131 has a half-life of eight days.
A sievert measures the biological effect of radiation absorbed. A microsievert is one-millionth of a sievert. A millisievert is one one-thousandth.
On average, Canadians receive about 2.7 millisieverts of ionizing radiation from natural sources in a year.
By comparison, the I-131 detected by Bruce Power corresponds to 0.003 per cent of the CNSC's effective dose limit of one millisievert per year to a member of the public and is an even smaller percentage of the total effective dose from all sources of radiation to which Canadians are exposed.
"The presence of these concentrations of I-131 in the air will not produce harmful effects to the health of Canadians," the commission said.
NB Power, operator of the Point Lepreau nuclear generating station, recently detected even smaller amounts of I-131. Researchers at Simon Fraser University also report finding trace amounts in seaweed and rainwater around Vancouver.
Health Canada says naturally occurring radiation provides 88.5 per cent of Canadians' average annual radiation dose, although it varies by region. You'll be exposed to twice as much ambient radiation if you live in Winnipeg as you'll receive if you live in Toronto.
Cross-country radiation monitoring by Health Canada has not shown an increase over and above normal day-to-day fluctuations. However, very minute levels of isotopes in the radiation have been attributed to the release in Japan, in the order of 0.0005 microsieverts a day, which is so small that it is extremely difficult to measure against normal background radiation.
Exposure from medical procedures such as dental X-rays, mammograms, CT scans and chest X-rays contribute about 11.5 per cent of the average citizen's yearly radiation dose.
Finally, commercial and industrial exposures — airport security scans, industrial X-rays, emissions from nuclear plants and, surprisingly enough, from burning coal in electrical plants — contribute 0.3 per cent.
Health Canada sets the safe maximum annual exposure for nuclear workers at 50 millisieverts, 100,000 times the level of Japanese radiation monitored in British Columbia, for example.
To put this in perspective, you'll get 0.0001 millisieverts just from eating a banana, about the same as walking through an airport security scanner.
And you'd have to walk through 1,000 airport security scans to equal your average chest X-ray.
Take a cross-country flight and you'll absorb around 0.04 millisieverts. Airline pilots, who fly all the time, get about 2.2 millisieverts per year.
A full-body CT scan might expose you to up to 30 millisieverts, many times the exposure to the radiation from Japan.
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