Rio Tinto loses tiny but dangerous radioactive capsule in 870-mile stretch of Australian outback

The substance cannot be weaponised, authorities say, but the public should stay clear if they come across it. Credit: AP

A tiny but highly radioactive capsule has been lost over a 870-mile stretch of Western Australia, with authorities left scrambling to find the potentially deadly substance.

The silver cylinder was part of a device believed to have fallen off a truck while en-route between a desert mine site and the city of Perth.

The caesium 137 ceramic source, commonly used in radiation gauges, emits dangerous amounts of radiation, equivalent to receiving ten X-rays in an hour.

It could cause skin burns and prolonged exposure could cause cancer.

Measuring just six millimetres by eight millimetres, people have been warned the capsule could have become lodged in a car tyre.

Mining giant Rio Tinto Iron Ore has apologised for the “alarm” it has caused communities.

The authorities are searching for the lost capsule. Credit: Department of Fire and Emergency Services

“We recognise this is clearly very concerning and are sorry for the alarm it has caused in the Western Australian community,” its chief executive Simon Trott said.

“As well as fully supporting the relevant authorities, we have launched our own investigation to understand how the capsule was lost in transit.”

The search has involved people scanning for radiation levels from the device along roads used by the trucks, with authorities indicating the entire 870-mile route – longer than the entire California coastline – might have to be searched.

Western Australia's Department of Fire and Emergency Services publicly announced the capsule had gone missing on Friday, two days after they were notified by Rio Tinto.

Mr Trott said the contractor was qualified to transport the device and it had been confirmed being on board the truck by a Geiger counter prior to leaving the mine.

Emergency services said they have been hampered by a lack of equipment and have called on the Commonwealth and other states to provide assistance.

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“What we’re not doing is trying to find a tiny little device by eyesight,” said Superintendent Darryl Ray, adding they were concentrating on populated areas north of Perth and strategic sites along the Great Northern Highway.

"We’re using the radiation detectors to locate the gamma rays,” he said.

Authorities were also using the truck’s GPS data to determine the exact route the driver took and where it stopped after it left the mine on or around January 10.

It is believed a screw became loose inside a large lead-lined gauge and the unit fell through a hole.

Chief Health Officer Andrew Robertson defended the Western Australia government’s decision to wait two days to inform the public on Friday, saying the mine and depot had to be searched and excluded, and the route confirmed.

He said the capsule was packed in accordance with the radiation safety transport and regulations inside a box bolted onto a pallet.

The public are warned not to go near the capsule. Credit: Department of Fire and Emergency Services

“We believe the vibration of the truck may have impacted the integrity of the gauge, that it fell apart and the source actually came out of it,” he said. “It is unusual for a gauge to come apart like this one has.”

Authorities ruled out theft at the depot before the box was opened on Wednesday.

Mr Robertson said members of the public should stay at least five metres away as contact could result in skin damage, burns and radiation sickness, including impacts to the immune and the gastrointestinal systems.

Long-term exposure could also cause cancer, however, experts say the capsule cannot be weaponised.

“Our concern is someone will pick it up, not knowing what it is, think this is something interesting (and) keep it,” Mr Robertson added.

Police determined the incident to be an accident and no criminal charges are likely.