Six people tested for possible radiation exposure have been released from hospital but remain under detention as suspects in the theft of a truck carrying highly radioactive cobalt-60, officials said Friday.
Of the detained men, ages 16 to 38, only the 16-year-old showed signs of radiation exposure and he was in good health, a spokeswoman for Hidalgo's Health Department said on condition of anonymity because she isn't allowed to discuss the case.
The six were detained Thursday as part of the investigation and taken to the general hospital in Pachuca for testing.
After being cleared by health authorities on Friday, the men were turned over to federal authorities in connection with the case of the cargo truck stolen Monday at gunpoint outside Mexico City. The cobalt-60 it was carrying was from obsolete radiation therapy equipment.
Officials have not said what roles the six allegedly had in the theft.
Hidalgo state Health Minister Pedro Luis Noble said earlier Friday the men suffered from skin irritations and dizziness, but that none were in serious condition. Only one was vomiting, a sign of radiation poisoning.
The theft triggered alerts in six Mexican states and Mexico City, as well as international notifications to the U.S. and the International Atomic Energy Agency in Vienna. It raised concerns that the material could have been stolen to make a dirty bomb, a conventional explosive that disseminates radioactive material.
The atomic energy agency said the cobalt has an activity of 3,000 curies, or Category 1, meaning "it would probably be fatal to be close to this amount of unshielded radioactive material for a period in the range of a few minutes to an hour."
But Mexican officials said that the thieves seemed to have targeted the truck, which has a moveable platform and crane, and likely didn't know about the dangerous cargo.
The six were arrested by Hidalgo state police, said state attorney general's spokesman Fernando Hidalgo.
The driver of the truck, who had stopped to rest at a gas station early Monday when the theft occurred, said two armed men made him get out, tied his hands and feet and left him in a vacant lot.
Hidalgo said he didn't know how or if the others were involved.
The truck was found abandoned Wednesday about 40 kilometers (24 miles) from where it was stolen, and the container for the radioactive material was found opened. The cobalt-60 pellets were left about a kilometer (half mile) from the truck in an empty rural field, where authorities said they were a risk only to those who had handled them and not to anyone in Hueypoxtla, the closest town of about 4,000 people. There was no evacuation.
The cobalt-60 was from a hospital in the northern city of Tijuana and was being transported to nuclear waste facility in the state of Mexico, which borders Mexico City.
Authorities maintained a 500-meter (yard) cordon around the site where the cobalt-60 still remains in the state of Mexico and continued to work Friday to extract it safely, said Juan Eibenschutz, director general of Mexico's National Commission of Nuclear Safety and Safeguards.
"It's quite an operation and it is in the process of being planned," he said. "It's highly radioactive, so you cannot just go over and pick it up. It's going to take a while to pick it up."