Queensland stewards have again warned trainers to be alert for horses inadvertently ingesting arsenic from wood shavings or yard posts.

There have been several cases across Australia of horses returning positive swabs to arsenic after eating treated timber.

The latest warning came after Sunshine Coast trainer Frank Phillips pleaded guilty to an arsenic-related charge for the second time.

An inquiry heard a swab taken from the Phillips-trained Jet'N' Wild returned a presence of arsenic after she raced at the Sunshine Coast on October 22.

Stewards fined Phillips $3000 after he was found to have previously been in breach of the rule in relation to arsenic.

On that occasion no action was taken after it was accepted that treated timber had been the source of the arsenic.

But stewards said Phillips had not taken sufficient steps to prevent Jet'N'Wild having access to the treated timber.

They also took into account Phillips previous unblemished record in 40 years of training.

Chief steward Allan Reardon said it was a problem across Australia and trainers should be aware of it.

"It will save them trouble if they make certain their wood products are not treated with arsenic," Reardon said.