Department of Fire and Emergency Services/AP
State authorities in Western Australia are searching for a tiny radioactive capsule believed to have fallen off a truck.
CNN  — 

It’s like looking for a needle in a haystack – an 8mm by 6mm silver capsule, no bigger than a coin, believed to be lost somewhere along a stretch of vast desert highway in Australia’s biggest state.

The reason authorities are so determined to find it is that it contains Caesium-137, a highly radioactive substance that’s potentially lethal.

Authorities in Western Australia believe the capsule, which emits both gamma and beta rays, fell off the back of a truck as it was being transported along a 1,400-kilometer (870-mile) section of the Great Northern Highway – a distance longer than the Californian coastline.

Mining company Rio Tinto, which used the capsule in a density gauge at its Gudai-Darri iron ore mine, apologized on Monday, saying it was supporting state government efforts to find it.

Rio Tinto said it has checked all roads in and out of the mine in remote WA, where the device was located before a contractor collected it for the journey south to the state capital, Perth.

Due to the tiny size of the capsule and the huge distances involved, authorities warn the chances of finding it are slim.

And there are fears that it may have already been carried further from the search zone, creating a radioactive health risk for anyone who comes across it for potentially the next 300 years.

Western Australia's Department of Health
An illustration provided by Western Australia's Department of Health shows the size of the capsule compared to a coin.

How did it go missing?

State authorities raised the alarm on Friday, alerting residents to the presence of a radioactive spill across a southern swathe of the state, including in the northeastern suburbs of Perth, home to about 2 million people.

According to authorities, the capsule was placed inside a package on January 10 and collected from Rio Tinto’s Gudai-Darri mine site by a contractor on January 12.

The vehicle spent four days on the road and arrived in Perth on January 16 but it was only unloaded for inspection on January 25 – when it was discovered the capsule was missing.

“Upon opening the package, it was found that the gauge was broken apart with one of the four mounting bolts missing and the source itself and all screws on the gauge also missing,” said the Department of Fire and Emergency Services (DFES).

They believe that strong vibrations caused by bumpy roads damaged the package – dislodging a mounting bolt that held it in place.

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How dangerous is it?

Experts have warned that Caesium-137 can create serious health problems for people who come into contact with it: skin burns from close exposure, radiation sickness and potentially deadly cancer risks, especially for those exposed unknowingly for long periods of time.

Radiation Services WA, a company that provides radiation protection advice, says standing within 1 meter (3.3 feet) of the capsule for an hour would deliver around 1.6 millisieverts (mSv), as much as around 17 standard chest X-rays.

Picking up the capsule would cause “serious damage” to your fingers and surrounding tissue, the company said in a statement.

Ivan Kempson, an associate professor in Biophysics from the University of Southern Australia, said the worst case scenario would be a curious child picking up the capsule and putting it in their pocket.

“This is rare but could happen and has happened before,” Kempson said. “There have been some past examples of people finding similar things and suffering radiation poisoning but they were much stronger than the current capsule that is missing.

“We are all exposed to a constant level of radiation from things around us and the foods we eat but the primary concern now is the potential impact on health of the person who would find the capsule.”

Department of Fire and Emergency Services/AP
State authorities are searching for the capsule along a stretch of the Great Northern Highway in Western Australia.

How rare is it to lose a radioactive device?

The incident has come as a shock to experts who said that handling of radioactive materials like Caesium-137 is highly regulated with strict protocols for their transport, storage and disposal.

Rio Tinto said it regularly transports and stores dangerous good as part of its business and hires expert contractors to handle radioactive materials.

Radiation Services WA says radioactive substances are transported throughout Western Australia on a daily basis without any issues. “In this case, there seems to be a failure of the control measures typically implemented,” it said, adding that it had nothing to do with the capsule’s loss.

Pradip Deb, a lecturer and radiation safety officer at RMIT University in Melbourne, said the loss of the capsule was “very unusual” as Australian safety rules require them to be transported in highly protective cases.

The name of the logistics company used to transport the device has not been released, Rio Tinto said.

Carla Gottgens/Bloomberg/Getty Images
A conveyor belt transports iron ore at the Gudai-Darri mine operated by the Rio Tinto in the Pilbara region of Western Australia, June 21, 2022.

Authorities have been searching along the truck’s route for days – from metropolitan areas of Perth in the south and much further north beyond Newman, a small town near the mine site.

They’re driving white vehicles with flashing hazard lights fitted with specialized radiation detection equipment slowly up and down the highway in both directions at 50 kilometers an hour (31 mph).

Dale Bailey, a professor of medical imaging science from the University of Sydney, said the slow speed was needed to give the equipment time to detect radiation from the missing capsule.

“Radiation detectors on moving vehicles can be used to detect radiation above the natural levels, but the relatively low amount of radiation in the source means that they would have to ‘sweep’ the area relatively slowly,” he said.

DFES Incident Controller Darryl Ray said as of Monday teams had searched more than 660 kilometers (410 miles) and authorities expect to complete the entire route by Friday.

If a member of the public stumbles upon the capsule in the meantime, authorities have urged them to stay at least 5 meters (16.4 feet) away – though they acknowledge it would be difficult to see from a distance.

“What we’re not doing is trying to find a tiny little device by eyesight. We’re using radiation detectors to locate the gamma rays,” DFES officials said.

But there are fears that it may no longer be within the search zone – authorities say the capsule may have become lodged in another vehicle’s tire, carrying it a greater distance away, or it could have even been dispersed by wild animals, including birds.

“Imagine if it was a bird of prey for example that picks up the capsule and carries it away from the (original) search area – there are so many uncertainties and it will pose more problems,” said Dave Sweeney, nuclear policy analyst and environmental advocate at the Australian Conservation Foundation.

“This source obviously needs to be recovered and secured but there are so many variables and we simply don’t know what could happen.”

What happens if it’s not found?

Caesium-137 has a half-life of about 30 years, which means that after three decades, the capsule’s radioactivity will halve, and after 60 years, it’ll halve again.

At that rate, the capsule could be radioactive for the next 300 years, said Deb from RMIT University.

“Caesium-137 is normally a sealed source – meaning, if it is not broken, it will not contaminate the soil or environment … If the capsule is never found, it will not contaminate or transfer radioactivity into the surrounding soil,” Deb added.

Kempson, from the University of Southern Australia, said that if remains lost in an isolated area, “it will be very unlikely to have much impact.”

Rio Tinto, one of the world’s biggest mining giants, operates 17 iron ore mines in Western Australia’s Pilbara region. The company’s mining activities have caused controversy in the past, including the destruction in 2020 of two ancient rock shelters at Juukan Gorge, prompting an apology and the resignation of then-CEO Jean-Sébastien Jacques.

With previous reporting from CNN’s Amarachi Orie.