A fish feed additive banned in the European Union because of its health impact on animals and humans has been found in Tasmanian salmon at concerning levels, reports The Guardian.

The compound, a synthetic antioxidant, is used to prevent fishmeal from spontaneously combusting while being transported at sea.

The Australian Pesticides and Veterinary Medicines Authority has set a maximum residue limit for ethoxyquin of 1 milligram per kilogram of salmon.

The testing commissioned by Christian Narkowicz, an organic chemist, found that ethoxyquin levels in three brands of Tasmanian salmon were within the maximum residue limits.

However, tests found that in Tassal and Petuna salmon there were significant levels of ethoxyquin dimer – two ethoxyquin molecules joined together – which form as the additive undergoes chemical changes.

Maximum residue limits should also take into account levels of the ethoxyquin dimer as it is considered to have the same toxic potential as ethoxyquin itself, said Stuart McLean, emeritus professor at the University of Tasmania.

The European Commission suspended the use of ethoxyquin as an animal feed additive in 2017 because experts could not agree on the safety of the additive.

A spokesperson for Petuna told The Guardian it predominantly sourced its feed from the Tasmanian company Biomar, which did not add ethoxyquin to its feed.

“Biomar has not detected any ethoxyquin in its finished goods in either 2021 or 2022,” it said.

The test results have not been provided to Petuna with any context and so the methodology, sample source and age of the results are unclear.

“Petuna commissions regular independent testing of salmon fillets using the National Measurement Institute … to quantify any residue of ethoxyquin, dimer and other trace chemicals," the company said.

The firm said its results to date indicated it had at no time exceeded maximum residue limits.

A spokesperson for Tassal declined to comment.