Australia’s Gina Rinehart was once the world’s richest woman, making a fortune on mining (now she is sixth).

A police investigation into possible attempted poisoning is underway after a worker at a remote mining company construction site in Western Australia noticed a bad taste as he started eating a meal.

The contractor employee also noticed discolouring in a piece of fruit he was served on Monday at the dining hall at the Pilbara site run by mining magnate Gina Rinehart’s Roy Hill company. He alerted staff who contacted police.

Analysis of the food item confirmed the presence of a dangerous chemical late on Wednesday, but it appears to be an isolated incident, with no similar reports since, police said.

It is not known what the intent of the poison was, or if there was a specific target.

Major crime squad detectives are investigating.