At least 76 radioactive devices—some of which could be used as a terrorist weapon—have gone missing in Canada over the past five years, reports the Edmonton Sun.

The Canadian Press compiled a database to show the rate at which widely used radioactive devices disappear. It found 35 were stolen by thieves, and three others were found in a roadside ditch, a garbage landfill and a farmer’s field. Thirty-two gauges, medical tools and other radioactive devices are still missing.

This information comes out as anti-terrorism experts warn that even low-level radioactive material can be built into crude radioactive explosives, otherwise known as dirty bombs.

Radiation safety experts say the missing radioactive devices pose a serious security risk. A dirty bomb can release radiation up to several miles depending on wind speeds and materials used, forcing evacuations and causing chaos. A study conducted by the Canadian government estimated that an explosion near the CN tower in Toronto could cost up to $23.5 billion.

In a study released last year, the Canadian Security Intelligence Service said it is “quite surprising” terrorists haven’t already set off dirty bombs, and that Canada was “positively overdue” for an attack.

However, Canada is not the only country struggling to keep its radiological equipment secure. The International Atomic Energy Agency found that between 1993 and 2005, member states (including the United States) confirmed more than 827 incidents of illegal acquisition, possession, and transfer or disposal of nuclear and other radioactive materials. This is most likely a conservative estimate, according to the U.S. Government Accountability Office, which has found more than 1,300 cases of radioactive sources lost or abandoned in the U.S. since 1998 alone.

Charles Ferguson, research leader on radiological threats and member of the U.S. Council on Foreign Relations, believes “it could be just a matter of time” before terrorists use dirty bombs. Just last September, Abu Hamza al-Muhajir, the now dead leader of al Qaeda in Iraq, called for scientists to build radioactive and biological weapons to use in terrorist attacks against American bases.

Readily accessible radioactive materials used by terrorists in America may be the next challenge in the war against terrorism.