However, some wild salmon also carry high levels of the chemicals in their flesh and some wild Chinook have the highest levels of all, the team at Indiana University reported.
Writing in the journal Environmental Science & Technology, the researchers said they tested salmon meat for polybrominated diphenyl ethers or PBDEs, which are used widely as flame-retardant additives in electronics and furniture.
Like PCBs and dioxin, they can build up in the flesh of animals and are especially high in carnivores.
Indiana University's Ronald Hites and colleagues measured PBDEs in 700 samples of farmed and wild salmon from around the world. The same team reported in January that they found high levels of chemicals in farmed salmon and blamed the "salmon chow" fed to the fish.
Salmon chow is a mixture of ground-up fish and oil fed to farm-raised salmon and scientists think it may be more likely to contain contaminated fish than the variety of foods eaten by wild salmon.
There is disagreement over whether PBDEs are dangerous. But Hites said he would be concerned.
"If you're a chemist and you draw the structure, they look a lot like PCBs," he said in a statement.
PCBs can cause cancer and reproductive, neurological and developmental defects.
In September 2003, the Environmental Working Group, which reports on levels of chemicals in the environment and other issues, said varying levels of PBDEs could be found in human breast milk.
The European Union banned two of the three most common PBDE products this year, and the state of California has banned two types of PBDEs beginning in 2008. Levels found in people's bodies are rising steadily.
The Bromine Science and Environmental Forum, which represents the industry, said action was already being taken to phase out the most dangerous PBDEs.
"As the sole manufacturer of penta-BDE (Great Lakes Chemical Corporation )has already announced to voluntarily cease production of this product by Dec. 31, 2004, these levels are expected to soon plateau, reverse course, and then decrease over time," it said in a statement.
Beginning next month, U.S. supermarkets will be required to put labels on salmon telling whether the fish is farmed or wild.
Consumers are being urged by doctors and the U.S. government to eat fatty fish such as salmon because of the high content of omega-3 fatty acids. These compounds are key for brain and eye development and can lower the risk of heart disease.