Recent studies surveying contaminant levels in farmed and wild-caught salmon have shown that, on average, farmed salmon contain substantially higher concentrations of a variety of persistent organic contaminants such as PCBs, dioxins, and pesticides. These studies indicate that wild salmon, being generally lower in toxic contaminants, is a healthier choice for consumers. However, closer inspection reveals that contaminant levels in individual fish can vary widely across wild and farmed salmon of various species and from various geographic regions, so the issue is not black and white.

Farmed Salmon ? Country of Origin is Key

The majority of salmon consumed in the United States today is Atlantic salmon raised on salmon farms. In the largest published survey of farmed salmon contamination, Hites et al. reported on levels of 14 chlorinated organic contaminants (mirex, DDT, endrin, dieldrin, cis-nonachlor, t-nonachlor, chlordane, heptachlor epoxide, lindane, hexachlorobenzene, toxaphene, PCBs, and dioxins) in approximately 700 farmed and wild salmon collected from around the world.[1] Fish were purchased at supermarkets in 16 large cities in North America and Europe, and directly from salmon farms in eight major producing regions of the world, including Scotland, Norway, Chile, Canada, Maine, and Washington State. This study found that all salmon contain detectable levels of various chlorinated contaminants. In particular, levels of certain contaminants were sufficiently high to trigger stringent consumption advice for farmed salmon from all locations, and for some species of wild Pacific salmon.

Among farmed salmon, fish produced in Chile and Washington State were found to be least contaminated. Farmed salmon from Scotland and the Faroe Islands had the highest contaminant levels. Canadian farmed salmon fell somewhere in the middle. According to Salmon of the Americas, an organization of salmon-producing companies, the vast majority of the salmon consumed in the United States and Canada are farmed Atlantic salmon produced in the Western Hemisphere. Chile leads in production, followed by Canada and then the U.S.[2]

Based on U.S. EPA cumulative risk assessment methods for cancer risk from mixed exposures to PCBs, toxaphene, and dieldrin, Hites et al. conclude that farmed salmon from Canada, Maine, and Norway should be eaten no more than once every two months, while Chilean and Washington State farmed salmon should be restricted to once a month. Farmed salmon from Scotland and the Faroe Islands were so contaminated that they shouldn?t be eaten more than three times per year. (Figure 1)

In a follow-up study using the same salmon samples, Hites et al. reported on levels of the brominated flame retardant chemicals known as PBDEs.[3] Similar to the first study, this survey found that, on average, farmed salmon contained higher levels of PBDEs than wild-caught Pacific salmon. As with the other contaminants, Scottish farmed salmon had the highest PBDE levels, while farmed salmon from Chile and Washington State had the lowest levels. While farmed salmon were generally higher in PBDEs than wild salmon, the researchers noted with interest that the highest PBDE levels measured in this study were in one sample of wild British Columbia Chinook. (Figure 2)

Wild Salmon ? Fat, Contaminant Levels Vary Widely Across Species

While in general wild Pacific salmon are less contaminated than farmed salmon, there is still wide variation in contaminant levels across the wild species.  This reflects both the diet of the salmon (larger fish eat higher up on the food chain, which leads to more contamination) and the age of the fish (older fish have had more years to accumulate toxicants). In addition to living longer, sockeye and especially Chinook salmon contain more fat than the smaller species.  Because PCBs and other persistent organic contaminants accumulate in fish oils, fattier salmon tend to be more contaminated. At the same time, fattier salmon tend to be more prized for color, flavor, and texture as well as concentration of nutrients such as omega-3 fatty acids. Therefore, the more expensive, ?gourmet? species of wild salmon that are most often served in restaurants and sold as fresh steaks and fillets will have the highest levels of contaminants. See Figure 3 below.

For example, Chinook (also known as king salmon) are most often served in high-end restaurants, and are generally marketed in whole steak, smoked and fillet forms. Hites et al. found that Chinook from Alaska are the most contaminated of all wild salmon, and are no cleaner than Chilean or Washington State farmed salmon. Coho (also known as silver salmon) and sockeye (also known as red salmon) are less contaminated than Chinook. At the ?clean? end of the wild salmon spectrum is chum salmon. Chum have a lower oil content than other salmon species, and Hites et al. found them to be the least contaminated wild salmon species. They are available as whole fish, steaks, fillets, smoked, and canned.

Finally, pink salmon are the most abundant of all wild salmon species harvested in Alaska, and typically the least expensive. They are relatively small fish compared with the other species, and have a low to moderate oil content. The state of Alaska did not report on levels of contaminants in pink Alaska salmon, but Hites et al. found this species to be among the least contaminated of all wild salmon. According to the Alaska Seafood Marketing Institute, pink salmon are marketed whole, as whole sides, smoked and canned.[4] They are not often sold as fillets or steaks in supermarkets or restaurants.

Recently, the state of Alaska released the results of its first significant effort to monitor levels of persistent organic contaminants in Alaskan fish.[5] Previous state monitoring efforts had found that levels of mercury in Alaskan fish and seafood were very low, but the state had conducted only limited sampling of Alaskan fish for PCBs, dioxins, persistent pesticides, and other pollutants. For its August 2004 report of contaminants in Alaskan fish, the state collected 600 samples of fish from marine water, rivers, and lakes throughout the state. However, only a small subset was analyzed for organic contaminants. In all, 59 salmon were tested, representing three of the five species of wild Pacific salmon ? chum (18), Chinook or king (17), and sockeye (24). The results are consistent with Hites et al. and other studies.

Canned salmon sold in the United States is typically wild Alaskan salmon.[6] Several salmon species are commonly canned, and can labels often denote the species. According to the Alaska Seafood Marketing Institute, the two most commonly canned Alaska salmon species are sockeye and pink. Chum salmon may also be purchased in cans. Canned pink and chum salmon are distinguished by their rosy color, soft texture, and mild flavor. Sockeye is the ?premier? canned salmon, with a deep red color, firmer texture, and higher price than the other canned varieties. As noted above, pink and chum salmon appear to be lowest in contaminants among wild species, while sockeye may contain higher levels.

The Culprits ? Pollution and Fish Farming Practices

Persistent organic pollutants like dioxins, PCBs, persistent pesticides, and the brominated flame retardants knows as PBDEs are ubiquitous in the global environment and in food supplies around the world. Many of these chemicals are, or once were, produced and used widely in various countries, and their extreme persistence, coupled with their ability to travel long distances on air and water currents and to bioaccumulate in food chains, means that they are widely dispersed in the global environment and food chains.

Wildlife and seafood from the cold waters of Alaska and other polar regions are particularly at risk of contamination from these pollutants because the pollutants tend to migrate around the globe and eventually settle and persist in cold climates.[7] The U.S. Environmental Protection Agency reports that even in Arctic Alaska, POPs have been found in the air, water, soil, plants, fish, and other wildlife.[8] Thus persistent pesticides from farms in Asia as well as industries in North America may find their way to Alaskan waters and then into the local food chain, including wild Alaska salmon.

However, it is feeding practices in fish farms around the world that account for the elevated contaminant levels in farmed salmon. In the wild, fish such as salmon can only feed upon fish and other creatures that are smaller ? and therefore typically less contaminated ? than they are. But salmon raised on farms are fed a diet that may consist of fish meal and oil derived from larger and more contaminated fish. Thus farmed-raised salmon are often eating above themselves on the food chain, a perverse situation that does not occur in the wild.

At present, the U.S. Food and Drug Administration (FDA) does not regulate the contaminant levels in feed produced for farm-raised salmon, nor does FDA monitor and regulate contaminant levels in farmed salmon imported into the United States. Until salmon farmers either voluntarily change their practices or are required to do so by strict FDA regulations, farmed salmon sold in the United States will likely continue to contain significantly elevated levels of toxic contaminants.

Consumers? Right to Know

Even without FDA action to reduce contaminant levels in farmed salmon, consumers can make informed choices to protect themselves with access to better information. Consumers have a right to ? and should demand ? easy-to-read consumer labeling and signage about salmon. Until now, most supermarkets and restaurants ? where most consumers buy fish ? have provided little or no information to consumers about the fish they sell, whether it is farmed or wild-caught, country of origin, etc. As the issue of mercury contamination of tuna and other fish has gained public attention, some states and localities have begun passing laws requiring stores and restaurants to post warnings about high mercury fish at the point of purchase. But consumers have been largely in the dark about levels of other toxic contaminants in store-bought salmon.

As of September 30, 2004, Country of Origin Labeling is now required for fish and shellfish under the 2002 Farm bill. This newly implemented law requires salmon to be labeled by country of origin and as either ?farmed? or ?wild.? In addition, the FDA now requires all farmed salmon products to be identified as containing artificial colorants. (These synthetic dyes are fed to farmed salmon to mask the natural gray color of their flesh, in contrast with the vivid pink-orange color that wild salmon derive from their natural diet of krill and other sea creatures.)

Improved labeling is an important step in helping inform consumers. Current law could be strengthened to require product labels and store signs that identify (1) genetically engineered ingredients or feed, (3) additives, (4) sustainability and/or organic certification, (5) nutritional value and (6) all major health-related issues such as antibiotic and pesticide usage, or other toxic contamination. This will enable consumers to make better informed, safe and more sustainable decisions in their selection of salmon and other seafood.

Conclusion

Although wild Pacific salmon are generally lower in toxic contaminants than their farm-raised Atlantic cousins, it is clear that contaminant levels in different species and individual fish can vary widely. More aggressive regulation of toxic pollutants in the environment and in fish feed is needed to reduce the levels of contaminants in both wild and farmed fish. In the meantime, consumers must seek out information about fish contaminants in order to make safe, healthy dietary choices for themselves and their families.

More information, including clinical and consumer fish consumption recommendations from Physicians for Social Responsibility and the Association of Reproductive Health Professionals, and a fact sheet on the health benefits of omega-3 fatty acids in fish such as salmon are available at www.mercuryaction.org/fish.

Acknowledgements

Author: Karen L. Perry, MPA, Deputy Director, Environment and Health Program, Physicians for Social Responsibility

PSR would like to thank Katherine M. Shea, MD, MPH and David O. Carpenter, MD for reviewing this fact sheet?s clarity and scientific and medical accuracy.