Racing Victoria stewards will not be issuing charges against four trainers who had horses return positive tests to arsenic.

Stephen Theodore, Gareth Andrews, Kelvin Southey and Shae Reynolds all had horses horses return arsenic levels above the 0.30 milligrams per litre of urine threshold following races between May and August 2015.

It was established the horses tested were stabled in yards with treated pine and post rail fencing and they had significantly chewed the fencing.

A number of wood samples were obtained from the yards with the analysis revealing arsenic at levels consistent with Copper Chromium Arsenic treated timber.

The University of Melbourne was engaged by several racing controlling bodies to conduct a study to establish if horses could exceed the arsenic threshold by ingesting timber treated with CCA.

The study revealed that some horses did exceed the urinary threshold.

As a result the trainers have been advised stewards will not be issuing charges against them.

Stewards have made an application to the Racing Appeals and Disciplinary Board for the disqualification of the horses from their respective races.

Two horses in Queensland were disqualified last year for high arsenic levels after consuming wood shavings with their trainers escaping penalty .