MEXICO CITY — A truck stolen near Mexico City with a load of a dangerous radioactive isotope used for medical purposes was found on Wednesday by the police after a two-day search, but some of the cargo was missing, a senior nuclear-safety official said.
The official, Mardonio Jimenez of Mexico’s nuclear safety commission, said a box containing some of the isotope, cobalt 60, was recovered with the vehicle, but that the whereabouts of the remainder was unclear. Cobalt 60 can be extremely dangerous when exposed to humans, and the theft has raised concerns of a more sinister motive, like the manufacture of a dirty bomb.
Counterterrorism officials, long concerned about dirty bombs, have said they are far more useful in spreading panic than in actually causing casualties or significant health concerns. Some experts say the bomb part might not be necessary — simply scattering a radioactive isotope in a densely populated area would have the same effect, but the person delivering the isotope would probably receive a large dose.
After the Sept. 11 attacks, the United States went on a campaign to ensure that cobalt 60 and other isotopes commonly used in medicine and industry were better protected against theft, so that they were less likely to be obtained for dirty-bomb use.
A United States military official said that while the Pentagon was monitoring the Mexico situation closely, the theft did not appear to be connected to any terrorist activity.
“I would say we are concerned but not worried,” said the official, who spoke on condition of anonymity. “No indication at all this was terror related – just simple vehicle theft. It was used medical-grade material on its way to a disposal site, so would have already decayed to the point that it would not be useful for a weapon even if it did fall into terrorist hands.”
The E.P.A. guide also warns that cobalt 60 is known to cause cancer. “Because it emits such strong gamma rays, external exposure to cobalt 60 is also considered a significant threat,” it says.
The Nuclear Threat Initiative, an anti-proliferation group, keeps a list of incidents involving theft, smuggling or unauthorized transport of radioactive materials, counting 15 incidents in 2012. It also noted the theft of cesium 137 in Estonia twice in the mid-1990s.