Farm-raised salmon contain much higher levels of flame retardants than most wild salmon, and some wild Chinook have the highest levels of all, according to new research. Building on an earlier study of chemicals in the two types of fish, the findings suggest that consumers should choose their salmon carefully.
The report appeared online Aug. 10 in Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.
Polybrominated diphenyl ethers (PBDEs), which are used widely as flame-retardant additives in electronics and furniture, are released into the environment both at their manufacturing sources and through everyday product wear and tear, according to the researchers.
They measured PBDEs in 700 samples of farmed and wild salmon from around the world, including most major salmon-producing regions. The study, which is by far the largest of its kind, used the same samples from an earlier study that revealed significantly higher levels of organochlorine chemicals like PCBs and dioxins in farmed salmon than in wild.
With one exception, they report, all farm-raised samples had much higher levels of flame retardants than wild salmon. They also found that farmed salmon from Europe had higher levels than those from North America, and that both European and North American farm-raised salmon had higher levels than those raised in the southern hemisphere.
One surprising outcome of the study was that wild Chinook salmon from British Columbia had the highest average PBDE levels of all the samples. "There’s something about Chinook that’s different, particularly with PBDEs," says the study’s lead author, Ronald Hites, Ph.D., an environmental chemist at Indiana University. The elevated levels could be related to the Chinook’s feeding behaviors, according to the researchers. Among all the wild species in the study, Chinook tend to feed higher in the food web and grow to be larger fish.
While it’s difficult to make direct comparisons, the concentrations found in farmed salmon are similar to levels that have been measured in people in recent years, Hites says.
The findings suggest that, in spite of the heart-healthy omega-3 fatty acids found in all salmon, consumers should limit their intake of farmed salmon and wild Chinook. They should also insist that all salmon be clearly labeled to indicate its source, the researchers say.
From the data in their earlier study on PCBs and dioxins, the researchers recommended eating two meals of farmed salmon per month or less, based on U.S. Environmental Protection Agency standards. But since no standards exist yet for PBDEs, a similar quantitative suggestion can’t be made.
Little is known about the specific toxic effects of brominated flame retardants, but public health officials are concerned because they have been associated in laboratory studies with various nervous system and reproductive effects, such as impaired learning and development.
There are other reasons for concern as well, according to Hites. "If you’re a chemist and you draw the structure, they look a lot like PCBs," he explains. "We have a long history of PCBs being environmentally persistent."
"Secondly, the concentrations are going up, and that seems to me to be a bad idea," Hites continues. While levels of all the organochlorine chemicals from the previous study are on the wane, PBDEs have been rising continuously for the past few years, he says.
Officials are still debating the fate of flame retardants in the United States, although the main U.S. manufacturer recently announced plans to discontinue their use as part of a voluntary agreement with the U.S. EPA. The European Union has banned two types of PBDEs — the penta and octa formulations — and is currently considering a ban on the deca formulation.
The American Chemical Society is a nonprofit organization, chartered by the U.S. Congress, with a multidisciplinary membership of more than 159,000 chemists and chemical engineers. It publishes numerous scientific journals and databases, convenes major research conferences and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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