Queensland stewards have warned trainers to watch for horses chewing shavings and fences which have arsenic treated timbers after two inquiries into high levels returned in swabs.

The warning comes after a long-running inquiry into a swab containing arsenic returned by runner-up Binalong Road after last year's Rockhampton Cup.

Stewards did not impose a penalty against Binalong's Road's Mudgee-based trainer Mack Griffith due to the unusual circumstances of the case.

Arsenic in excess of the threshold was found in a urine sample taken from Binalong Road on June 25, 2016 with the horse disqualified from his placing on Friday.

After giving evidence Griffith pleaded guilty to bringing a horse to race with a prohibited substance detected in any sample taken pre or post race.

Chief steward Allan Reardon said the charge was one where matters concerning the reasons for its presence were relevant to penalty.

"Stewards considered a study by the Melbourne University faculty of Veterinary Agricultural Sciences which examined the ingestion of wood shavings containing arsenic and the elevated levels achieved," Reardon said.

"The stewards could therefore not exclude to the requisite standard that the level of arsenic was not the result of Binalong Road consuming wood shavings used as bedding in its stable."

There was no other evidence regarding administration of products containing arsenic.

In another arsenic case, stewards gave similar reasons when they disqualified Horta Sexta from a win at the Gold Coast last year.

Stewards found again as there was no evidence an arsenic based substance was administered to Horta Sexta they did not penalise trainer Bill Pholi.