MEXICO CITY — Six people have been arrested in connection with the theft this week of a truck carrying highly radioactive waste in an episode that caused an international scare and raised concerns about the transporting of nuclear material.

The group was arrested Thursday night and taken to a hospital in Pachuca, 60 miles north of here and not far from the small town where the truck and the material, cobalt 60, were found Wednesday after armed robbers stole them Monday.

One of the people, a 16-year-old boy, was vomiting and had signs of possible radiation sickness, while the others were taken to the hospital as a precaution before all were cleared and released in the late afternoon and turned over to the federal police.

The material, hospital waste being transported from Tijuana to a storage repository near Mexico City, is often cited as a potential ingredient in a dirty bomb, a combination of explosives and radioactive material, though Mexican and American officials said the theft appeared to be a common crime and not related to terrorism.