THE CANADIAN PRESS -- OTTAWA - Some medical specialists and other workers have been overexposed to radiation, a few getting doses high enough to change their blood chemistry and even cause radiation sickness, The Canadian Press has learned.
An analysis of an internal government database shows instances in which workers were exposed to doses of radiation well beyond regulatory limits.
Radiation doses are measured in millisieverts (mSv). Doses as little as 50 to 100 mSv can cause detectable changes in blood chemistry, although normally it takes more than 500 mSv before signs of radiation sickness appear.
The provinces set dosage limits for people who work around radiation, including X-rays. For eight provinces, the most that workers' bodies are supposed to be exposed to in a year is 50 mSv. The exceptions are British Columbia and New Brunswick, where the annual limit is tougher, at 20 mSv.
But an analysis of government dose records found more than 100 instances in the last decade where workers were exposed to more radiation than provinces set out in their yearly limits -- sometimes far beyond what is considered safe.
Last year, an office worker in Ontario was exposed to 2,768 mSv of radiation over the month of May. The U.S. Environmental Protection Agency says that's enough of a dose to cause changes in blood chemistry, nausea, fatigue, vomiting, hair loss, diarrhea and hemorrhaging.
An Ontario industrial radiographer, whose job it is to inspect objects and products for flaws by using X-ray machines, was exposed to 2,717 mSv over a 16-day period in May 2000.
Three more industrial radiographers got high doses of radiation. The highest was a British Columbia radiographer's 1,351 mSv-dose over the last two weeks of January 2006.
An industrial worker in B.C. is listed as being exposed to about 10,000 mSv over a three-month period in 2005 -- almost certainly an erroneous entry, because such a dose would destroy the lining of the intestines and cause internal bleeding and death within two weeks.
A radiation expert at McMaster University in Hamilton said some of the highest doses are cause for concern.
"That would be fairly high exposure," said Dr. John Luxat, the Natural Sciences and Engineering Research Council's industrial research chair in nuclear safety analysis.
The bulk of the cases were below the 500-mSv threshold but still above the regulatory limits set by the provinces. Some records didn't give a dose.
These cases are few compared with the millions of entries that do fall within the provinces' prescribed limits. But the overexposures raise questions about the health and safety of some radiation workers.
The radiation protection bureau of Health Canada keeps dose records of radiation workers in Canada going back to the 1940s in a database called the National Dose Registry.
The information comes from so-called dosimetry providers, who monitor workers for radiation exposure and report back to the keepers of the National Dose Registry.
The Canadian Press obtained partial dose records from 2000 to 2010 under the Access to Information Act. The department wouldn't release any information that could be used to identify individual workers or their workplaces.
The job of industrial radiographer, with 21 entries, was the type most often overexposed to radiation. Instrument technician followed with 11 entries, and radiation therapist came in third with nine entries.
The types of jobs that appeared the fewest times, with one entry apiece, were dental assistant, dentist, fuel processor, medical laboratory technician, therapeutic radiologist, general maintenance worker at a nuclear reactor and hospital ward orderly.
Ontario had the most entries, with 41. Nova Scotia, with just a single entry, had the fewest.
No one from Health Canada was available for an interview.
In a statement, the department said it's rare that workers get enough of a dose of radiation to hurt them.
"Exposures in the workplace that are large enough to cause an injury or disease in the short term are extremely rare; however, depending on the magnitude of the exposure, they may increase the risk of certain types of cancer," spokesman Gary Holub said in an email.
"Exposures in excess of regulatory limits are handled by regulatory authorities who have the power to order an investigation and to restrict workers from further work with radiation for a period of time. Treatment for any injury or disease from radiation is a provincial responsibility."
It would be hard to tell if doses at the lower end of the scale caused the workers any health problems. But the signs of high exposure should be fairly obvious.
"When you get higher up, then clearly you do see ... some signs of radiation sickness, such as vomiting, some things like that," Luxat said.
The average person who doesn't work around radiation gets a dose of roughly three mSv a year, he added.
Canadians are exposed to low levels of radiation every day when they bask in the sunshine, chat on cell phones or heat up meals in the microwave.
Long-term exposure to radiation can damage bone marrow and increase the risk of developing cancer.
This week, the cancer agency of the World Health Organization said exposure to the type of electromagnetic radiation emitted by wireless devices may put people at greater risk of a rare but often deadly form of brain tumour.