How a Disused Medical Device Contaminated Thousands of American Homes

Summary

In 1983, an unused cobalt-60 radiotherapy machine was dismantled at a medical center in Ciudad Juárez, Mexico, and sold as scrap. Its radioactive source escaped its protective casing and contaminated scrap metal, which was melted into steel and distributed across Mexico and the United States. The contamination was discovered in January 1984, when a truck carrying steel rods triggered radiation alarms near Los Alamos National Laboratory.

How the contamination spread

• The machine contained a sealed source of 1,003 curies of cobalt-60. It had four intended safeguards: cobalt in solid pellets, welded steel capsules, a thick lead treatment head, and regulatory permits and registration. The machine had been imported without the required approvals and left unused in storage.
• In December 1983, maintenance worker Vicente Sotelo and his colleague Ricardo Hernández dismantled the machine to sell it. During the process, the capsule was breached, scattering cobalt pellets into the truck and scrapyard.
• Scrap contaminated with pellets was moved by electromagnetic crane and sent to a steel mill. The mill’s furnaces melted the scrap at about 1,600°C.
• Cobalt’s melting point is about 1,495°C, while its boiling point is nearly 3,000°C. It did not evaporate during smelting; instead, it dissolved into the steel. The video reports that more than 90% remained in the finished metal. Smelting spread the radioactive material through large quantities of steel rather than eliminating it.
• The steel was made into reinforcing bars and about 30,000 restaurant table bases, which were shipped to U.S. states, Puerto Rico, and the Virgin Islands.
• Sotelo’s truck also broke down in a residential area of Juárez and remained there for 40 days. Its cargo box was later measured at up to 1,000 roentgens per hour. Radiation could not be seen or felt, and nearby walls offered little protection.

Detection and investigation

• On January 16, 1984, a truck carrying steel rods passed over radiation sensors near Los Alamos. The alarms prompted staff to scan the cargo, revealing that radiation was distributed throughout the steel rather than limited to its surface.
• Gamma spectroscopy identified cobalt-60 by its characteristic energy peaks at 1.17 and 1.33 million electron volts.
• Investigators traced the steel using its production “heat” numbers—unique batch identifiers stamped on products and recorded in mill production books. Comparing the numbers with Aceros de Chihuahua’s records linked the contaminated steel to scrap processed on December 10 and to a scrapyard in Ciudad Juárez.
• U.S. and Mexican authorities closed the plant and searched for further contamination. U.S. Army helicopters equipped with detectors helped locate Sotelo’s abandoned truck. The surrounding area was then cordoned off, and residents were evacuated.

Consequences and cleanup

• The contamination map covered 17 Mexican states and more than 20 U.S. states. Of 17,000 inspected structures, 814 were deemed impossible to remediate and were demolished.
• About 4,000 people received some level of exposure. The video reports that most received less than half a rem, while more than 80 people received over 25 rem. Some families living near the truck received over 100 rem; five reportedly received between 300 and 700 rem over two months.
• Two scrapyard workers were reported to have been left permanently sterile. The official record listed no fatalities. A family later said scrap worker Antonio Favela died of radiation exposure, but the video notes that no death certificate or medical record confirmed this.
• No one was convicted. Sotelo said he had been instructed to remove the machine; the hospital director said it was taken without authorization. The theft was never proven.
• Recovered contaminated material was taken to a disposal site in the Samalayuca Desert. The final inventory included contaminated soil, slag, gypsum, reinforcing bars, scrap, and table bases—more than 36,000 tons in total. Some contaminated steel was recovered, some was buried, and some was never found.

Researchers and sources featured

No individual researchers are named in the subtitles. The investigation and response involved:

• Los Alamos National Laboratory health and physics team
• U.S. Nuclear Regulatory Commission (NRC)
• Mexico’s National Commission for Nuclear Safety and Safeguards (CNSNS)
• U.S. Army helicopter detection teams