August 10, 2004
Public health authorities are concerned about these substances, known as polybrominated diphenyl ethers (PBDEs), because they have been associated in scientific studies with behavior and nervous system effects such as impaired learning and memory, reproductive effects, and endocrine system effects that could impair growth and development. The European Union and the state of California have banned several of these substances.
The group of flame retardant chemicals is used in electronics, upholstery, and other consumer products and migrate from the environment into the food web when these products are disposed. The amounts of PBDEs detected in people and wildlife appear to have doubled in North America every four to five years since the 1970s, a pace unmatched by any other contaminant. Electronics companies including Sony and Toshiba and at least one major furniture maker, Ikea, have phased out PBDEs from their products.
The findings released this week build on a January study published in Science which found that farmed salmon contained significantly higher levels of cancer-causing PCBs, dioxins, and some pesticides than did wild salmon. That study concluded that concentrations of some contaminants were so high that more than one meal of farmed salmon per month could pose unacceptable cancer risks. The majority of salmon served in restaurants and found on grocery store shelves is farmed rather than wild.
Because government agencies and international health authorities have not set acceptable exposure levels for PBDEs, the authors did not identify any recommended consumption levels for salmon containing the chemicals. While the effects of PBDEs on human health are not nearly as well understood as the carcinogens found in farmed salmon, there is growing concern among scientists and many health authorities about the possible health impacts of exposure to PBDEs.
According to Ronald Hites, Distinguished Professor at Indiana University and lead researcher on the study, "PBDEs are structurally similar to PCBs, which have been linked to cancer and to reproductive, neurological, and developmental effects in humans. Even though no quantitative risk estimates have been done for PBDEs, public health experts are concerned because the concentrations of these substances in people have been increasing so rapidly."
The Pew Charitable Trusts, one of the U.S.'s largest philanthropies, sponsored the study. Pew has sponsored major research on fisheries, including a number of widely reported recent studies on the deterioration of the marine environment.
Largest Sampling Yet Published
The data on PBDE concentrations in farmed and wild salmon come out of the world's largest scientific sampling of salmon yet published in a recognized peer-reviewed journal. The study analyzed fillets from about 700 farmed Atlantic salmon and wild Pacific salmon. The farmed salmon was produced in each of the eight major farmed salmon producing regions in the world or purchased in 16 large cities in North America and Europe. The study's authors, six U.S. and Canadian researchers representing fields from toxicology to biology to statistics, selected salmon samples to be representative of the salmon typically available to consumers.
Salmon farmed in Europe were generally more contaminated with PBDEs than salmon farmed in North America. But North American farmed salmon were more contaminated than salmon farmed in Chile. Similarly, PBDE concentrations in salmon purchased from retail outlets in Europe-including Edinburgh and London-were generally higher than concentrations in salmon purchased in stores in North America-including Washington, D.C., New Orleans, Denver, and New York. Most of the salmon sold in European stores comes from European farms. Much more of the salmon sold in U.S. stores comes from Chile and Canada.
While wild salmon as a group were generally the least contaminated with PBDEs, PBDE concentrations were highest in wild Chinook from British Columbia and in farmed salmon from Scotland and Western Canada. The lowest concentrations of PBDEs were found in the other wild salmon and in farmed salmon from Chile and Washington State.
One unusual finding involved the relatively high PBDE concentrations in the wild Chinook samples. The authors found significant and unexpected differences in PBDE concentrations among the different species of wild salmon suggesting that different feeding behavior-for example, chinook tend to feed higher on the food chain-and other biological differences among the species could account for these differences.
Reason for Contamination
The authors concluded that the contamination problem is likely related to what farmed salmon are being fed. While most wild salmon eat a diverse diet of aquatic organisms from lower in the food chain, farmed salmon are fed a high fat diet containing a concentrated mixture of ground up fish and fish oil. Since chemical contaminants fish are exposed to during their lives are stored in their fat, the high fat farmed salmon food passes along more of these contaminants to the farmed salmon.
Polybrominated diphenyl ethers (PBDEs) serve as flame retardants in a wide variety of commercial and household products. Annual sales of PBDEs are around 70,000 metric tons. PBDEs likely migrate from the products in which they are used into the environment, up the food chain, and into the human body through the use and disposal of plastics and foam containing PBDEs. Found in air, water, fish, birds, marine mammals, and people, PBDEs are now ubiquitous, and the concentrations of these compounds have increased markedly over the last 20 years.
The authors conclude in their study that their results demonstrate the importance of labeling salmon as farmed and identifying the country of origin.
What Consumers Can Do
While the health benefits associated with the omega-3 fatty acids in all salmon have been well documented, the authors suggest that consumers concerned about the levels of any contaminants they might be exposed to from farmed salmon have many options. Many other food sources of omega-3's do not contain carcinogens and PBDEs to the degree they now exist in farmed salmon. These alternatives include some wild salmon as well as other fish that are not raised on contaminated feed.
Beginning next month, supermarkets will be required to label salmon farmed or wild along with country of origin under a 2002 law. Salmon purchased in restaurants and fish markets are not covered by this law. Consumers should be aware that the word "Fresh" on the label does not mean the salmon is wild-caught from the ocean. And any salmon labeled "Atlantic" in the U.S. is almost always farmed. Salmon labeled "Atlantic" in other countries is most likely farmed.
The annual global production of farmed salmon has increased 40 times during the last two decades-making inexpensive salmon available to consumers year-round. Between 1987 and 1999, salmon consumption increased at an annual rate of 14 percent in the European Union and 23 percent in the U.S. Japanese salmon consumption doubled between 1992 and 2002. Since 2000, over half of the salmon eaten globally has been farmed, coming primarily from fish farms in Northern Europe, Chile, Canada, and the United States.