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Radioactive lab material, which may have been sent to scrapyard, are considered low risk by nuclear safety commission.Charla Jones/The Globe and Mail

A small amount of radioactive material has mysteriously disappeared from a Toronto research facility.

The Sunnybrook Research Institute (SRI) announced Wednesday evening that a locked, lead-lined cabinet containing radioactive material went missing some time after June or July of last year. The working theory is that the cabinet was mistakenly sent to a scrapyard, said Michael Julius, the institute's vice-president of research.

Although SRI is located at Sunnybrook hospital, Dr. Julius said the missing cabinet is not a threat to patients. "There is no impact on patient safety. I really do want to underscore that," he said.

Staff at SRI first noticed the cabinet was missing during a routine audit on March 21. The cabinet, a heavy 75-cubic-centimetre object, was clearly labelled as containing radioactive material.

Inside were 14 radioactive items, only one of which poses a potential health risk, Dr. Julius said. That item, about half the size of a dime and used to calibrate X-ray machines, contains the radioactive isotope Americium-241, commonly found in smoke detectors. It was encased in its own locked, lead-and-steel box inside the cabinet. "If you managed to get it out of the smaller box – which would be a feat, I have to tell you – if you were to put it in your pocket, for example, and left it in your pocket for a day or two, you could get a radiation burn," Dr. Julius said.

After the March 21 audit, SRI reported the missing material to the Canadian Nuclear Safety Commission, which gave the institute 21 days to figure out what happened to the cabinet. SRI determined that the cabinet was last accounted for during a safety audit in June or July of 2013, after which the room in which it was stored was cleaned out by non-expert janitorial staff and possibly sent by mistake to a scrapyard.

But Dr. Julius cautioned that is just SRI's best theory at this point.

The 21-day period expired Wednesday and SRI has officially declared the cabinet lost.

The missing items are considered "category five," meaning they pose the lowest risk on the nuclear safety commission's risk scale.