Lab still studying poisoned Roy Hill fruit

A Perth laboratory is still trying to work out how cyanide got into a kiwifruit served at a mine site in WA's Pilbara region.

A worker at the Roy Hill mine noticed a bad taste when he bit into the fruit on Monday, and also saw it was discoloured.

He alerted mess hall staff who contacted police.

Analysis at the ChemCentre in Perth confirmed the presence of a dangerous chemical late on Wednesday.

On Friday, police said the laboratory was continuing to work out how cyanide was put in the fruit.

"There have been no further reported incidents since this matter was reported on Monday, indicating that this has been an isolated incident," police said.

They said mine staff had co-operated fully with the investigation.

The worker has been tested and shown no signs of health problems.

WA Police Minister Liza Harvey said the incident was highly concerning.