A tiny radioactive capsule lost in the outback has been found three weeks after it went missing.

The capsule – which could fit onto a 10 cent piece – came loose during transportation from north of the Pilbara mining town of Newman to the Perth suburb of Malaga some time between January 10 and January 16.

There were fears that long-term exposure to the item could cause cancer.

However, it has now been found after a search along a 1000km stretch of road - and it was just 2m from the roadside, not far from where it started its journey at a Rio Tinto mine.

“The search groups have quite literally found the needle in the haystack,” WA Emergency Services Minister Stephen Dawson said.

The small, round, silver capsule, 6mm in diameter and 8mm high, is used within gauges in mining operations and contains a small quantity of radioactive Caesium-137.

The radioactive capsule is smaller than an Australian 10c coin. Photo / DFES

But chief health officer Andrew Robertson said despite its size, the capsule contained “quite a large radiation dose”.

Dr Robertson said it was like “receiving around 10 X-rays an hour … the amount of natural radiation we would receive in a year just by walking around”.

He warned people against picking it up, saying more severe health conditions including cancer could stem from prolonged exposure.

A Rio Tinto spokesperson confirmed that the missing capsule was lost by an expert radioactive materials handler.

Rio Tinto was working with the Radiological Council, the contractors and emergency services to assist the search.

DFES Acting Superintendent Darryl Ray told reporters on Saturday firefighters would be using GPS data from the truck used to transport the capsule to find where it might have fallen from the vehicle.

“What we’re not doing is trying to find a tiny little device by eyesight,” said Mr Ray, who said they would be using a device that could detect the radiation from the capsule within 20m.

Acting Superintendent Ray also gave more details on the movements of the capsule before it was noticed missing.

It was packed onto a pallet at Rio Tinto’s Gudai-Darri mine site on January 10, with the pallet loaded onto the back of a semi-trailer and left the site for Perth between January 11 and 14.

It arrived at a radiation service company in the northern suburb of Malaga on January 16, but the capsule wasn’t noticed missing until the pallet was unpacked on Wednesday, when the alarm was raised.

DFES said while risk to the community was relatively low, exposure to the substance could cause radiation burns or radiation sickness.

“People could end up developing redness of the skin, and eventually burns from beta radiation. If it’s kept long enough there could be more acute effects, including effects on their immune system and on their gastrointestinal system,” said Dr Robertson.

- Anthony Anderson, news.com.au