Farmed salmon may contain banned toxic chemicals linked with developmental problems in children, warns new research.

The study found that farmers could be using feed that contains a type of synthetic flame retardant imported from countries "without advanced food safety regulations".

Salmon grown in environments free of polybrominated diphenyl ethers (PBDEs) could still contain dangerous amounts of the chemical as a result, according to the findings.

New models on how the chemical enters food chains show it could also affect feed for cattle and sheep as well.

Dr Carla Ng, assistant professor of civil and environmental engineering at the University of Pittsburgh's Swanson School of Engineering, said: "The United States and much of Europe banned several PBDEs in 2004 because of environmental and public health concerns.

"PBDEs can act as endocrine disruptors and cause developmental effects. Children are particularly vulnerable."

Despite restrictions on their use, PBDEs were classed as "persistent organic pollutants" at the Stockholm Convention, an international environmental treaty, in 2009.

Dr Ng's paper said they continue to be found in areas that process large amounts of electronic waste and with poor recycling regulation such as China, Thailand and Vietnam.

She said: "The international food trade system is becoming increasingly global in nature and this applies to animal feed as well.

"Fish farming operations may import their feed or feed ingredients from a number of countries, including those without advanced food safety regulations."

Conventional models to predict human exposure to pollutants mostly look people's risk from their local environment.

But Dr. Ng's model takes into account factors to find "the best predictor" of PBDEs in farmed salmon.

These included pollutants inhaled through gills, how the fish metabolised and eliminated pollutants, and the concentration of pollutants in the feed.

She said: "We found that feed is relatively less important in areas that already have high concentrations of pollutants in the environment.

"However, in otherwise clean and well-regulated environments, contaminated feed can be thousands of times more significant than the location of the farm for determining the PBDE content of salmon fillets."

She added the model could be applied in other fish with large global markets such as tilapia or red snapper and to predict pollutant content in livestock or feeds produced in contamination "hot spots".