Contact an expert who can comment on the study
The complete study
Summary of the study
Consumption recommendation data at a glance
Frequently asked questions and answers about the new study
What can consumers do to limit their exposure?
Some of the contaminants found in farmed salmon
How the study's farmed salmon consumption recommendations were determined
Background information about world salmon production and consumption
Several small, peer-reviewed pilot studies on farmed salmon
About the study's authors
Frequently Asked Questions about the Science Study on Contaminants in Farmed Salmon
Why were the levels of several contaminants higher in farmed salmon than in wild salmon?
The big differences between farmed and wild salmon contaminant concentrations are most likely a result of their diet. While wild salmon eat a large variety of aquatic organisms where they feed such as krill, zooplankton, and small fish, farmed salmon consume a formulated high-fat feed primarily of other fish ground into fishmeal and fish oil. Fishmeal feed is used to encourage rapid growth. Most fish retain man made chemical contaminants in their fatty tissues. Because of their almost exclusive diet of fishmeal and fish oil, farmed salmon consume higher concentrations of the fatty tissue of other fish than do wild salmon. The differences in contaminant levels of farmed salmon from different regions are likely related to differences in the contaminants in the feed.
Where did the contaminants found in salmon feed come from?
Vast quantities of industrial and agricultural chemicals have been deposited into the oceans for the last 50 years. Even contaminants no longer in use can be found in sediments on the ocean floor. Now banned PCBs were used as fire retardant insulators and continue to enter the oceans from leaking equipment, illegal dumping, and disposal of PCB laden equipment in hazardous waste sites. Dioxins are deposited into the ocean from the air and are emitted during waste incineration, chemical manufacturing, paper bleaching, and a variety of other processes. Toxaphene and dieldrin were popular pesticides used in agriculture and washed off of fields and into the ocean. Since most of these contaminants are fat soluble, they collect in the fat of ocean fish that are exposed to them. Since fishmeal is produced from ground fish and fish oils (which are high in fat), high levels of these contaminants end up in salmon feed.
Are there other health risks besides cancer associated with the contaminants found in farmed salmon?
There are many potential non-cancer health risks associated with these contaminants even though no intake levels or consumption guidelines have been set for them. For example, PCBs have been linked to reproductive and developmental effects in humans and animals, and exposure before birth has been linked to lower IQ, hyperactivity, shortened attention span, and delayed acquisition of reading skills. Dioxins have been linked to reproductive and developmental effects, altered immune function, and disruption of the endocrine system. And exposure to toxaphene and dieldrin can damage the nervous system. Some of these risks particularly some neurological and immune system effects have been found to occur at lower exposure levels than those set for limiting cancer risk.
Are there other health-related differences between farmed and wild salmon such as the levels of omega-3 fatty acids? And do the omega-3 benefits of eating farmed salmon outweigh the harmful effects of the contaminants?
This study does not report on omega-3 fatty acids in different types of salmon, but rather reports risks of cancer in that it looks at a number of contaminants that are known or probable carcinogens. Omega-3 fatty acids have not been shown to be protective against cancer but are associated instead with a reduced incidence of sudden cardiac death from arrhythmias. However, others have reported that dioxins and PCBs increase risk of heart disease because they increase the levels of cholesterol and lipid production by the liver. Therefore, these contaminants may counteract some of the beneficial effects of omega-3 fatty acids in protecting the heart.
A number of other beneficial effects of omega-3 fatty acids have been suggested but are not well proven. These include improved cognitive development of human fetuses, improved immune function, and prevention of diseases such as Alzheimer's Disease. However, the contaminants measured in the recent study are known to have adverse effects on IQ and immune function, so here as well the contaminants may counteract some of the possible beneficial effects of the omega-3 fatty acids. Intake of omega-3 fatty acids from foods that do not contain high levels of environmental contaminants is good, and there are many such foods available. These include wild salmon and other wild ocean fish, canola and flax seed oils, and some legumes.
Are the levels of contaminants you found in farmed salmon significantly greater than levels consumers might be exposed to from other foods?
A lot more research needs to be done to understand the levels of environmental contaminants individuals are exposed to from their food. The most systematic analysis of contaminants in food has been recently reported by the FDA in their Total Diet Study, 1991-2001, which looked at levels of many different contaminants in a variety of foods.
In general, the levels of these contaminants are higher in fat-containing foods, including meat, fish, dairy products and eggs, than in fruits and vegetables. Many of the contaminant concentrations found in farmed salmon and reported in the Science study were two to ten times higher than what FDA reports in meats and cheese.
Why did the study's authors use U.S. Environmental Protection Agency (EPA) fish consumption guidance governing locally caught fish rather than U.S. Food and Drug Administration (FDA) standards governing commercially sold fish?
Because the authors were interested in performing a health-based study and arriving at meaningful conclusions about the true health risks of consuming farmed salmon, they used EPA methods that take only human health risks into account. This approach to setting consumption advisories has been accepted by many states. Because FDA standards are set by considering a range of factors in addition to health such as the costs and commercial impacts of regulatory action FDA standards would not have been useful in arriving at purely health-based conclusions. Furthermore, while EPAís methods were developed within the last few years, FDA standards for PCBs and dieldrin were first proposed more than 25 years ago. In the meantime, not only has new technology allowed scientists to detect PCBs at much lower levels, but many new studies have come out detecting health effects for these substances at these lower levels. Also, since Americans eat more fish today than they did 25 years ago, they are exposed to higher levels of PCBs than FDA contemplated when it set its standards. The older FDA standards obviously do not take this new science and new diet information into account. FDA has no action levels or tolerances for toxaphene in fish.
If the risk to human health from consuming contaminants in farmed salmon is so great, why hasnít the government done anything about it?
EPA methods are used by states and the EPA itself to issue fish consumption advisories based on human health effects, but FDA is the agency that would have to act to restrict the sale of farmed salmon. The levels of contaminants found in farmed salmon, while triggering relatively restrictive consumption advice from EPA, do not exceed FDA action levels. Even though scientific information suggesting greater health risks from PCBs, dioxins, pesticides, and other substances has been gathering for more than 15 years, information about the extent of the publicís exposure to these substances - especially from animal fat in the diet - is relatively new. Having been set in some cases as long as 25 years ago, FDA standards for several environmental contaminants do not reflect the latest scientific information. Perhaps for many of these reasons, both EPA and FDA agree that the FDA levels are inappropriate for setting fish consumption advisories (see last paragraph on p. 1-5 in EPA National Guidance for Fish Advisories).
What could consumers do if they are concerned about the results of the study?
There are steps consumers could take to reduce their risk if they were concerned about contaminant levels in farmed salmon. Individuals could limit their consumption to on average no more than one farmed salmon meal per month. However, consumers need to be aware that in some cases even that could exceed advised contaminant exposure levels. Consumers should ask where the farmed salmon comes from. If it comes from Chile or Canada - which is the source for the majority of salmon in the U.S. - then no more than one to two meals per month is recommended. However, farmed salmon from the North Atlantic - which is predominant in Europe and can be purchased in North America - should be limited to much less than one meal per month. One option would be to make efforts to consume wild rather than farmed salmon or to choose to eat other kinds of fish that feed lower on the food chain or from diverse food sources. Since contaminants are deposited in the fatty tissue of the fish, consumers may be able to reduce their consumption of contaminants by removing as much skin and visible fat as possible. However, it is difficult to determine how much of the contaminant load can be removed in this way. The scientific literature is inconclusive as to the effectiveness of this method.
How can consumers know they are eating farmed or wild salmon?
Both wild and farmed salmon are widely available in grocery stores and restaurants and may or may not be labeled as such or listed on the menu. Some supermarkets and fish markets will label wild salmon but not farmed salmon. However, this is not always the case. It is always wise to ask, particularly to determine what country the farmed salmon comes from. It is difficult to determine what kind of salmon may be for sale based on the time of the year and the availability of fresh wild salmon because consumers can buy frozen wild salmon "thawed for your convenience..." at any time of year. 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.
Are certain consumers more at risk from consuming farm raised salmon than other consumers?
Children (particularly young girls), women of childbearing age, and women who are pregnant or nursing should be more concerned about exposure to these substances. Childrenís developing systems are more vulnerable to a variety of toxic exposures. And since these substances persist in a personís body for many years and can be passed on to a fetus during development - causing many harmful effects - it is particularly important that young girls and women of childbearing age avoid excessive exposure to these substances. A girl who eats contaminated fish at age 10 will still have half of the contaminants in her body when she is age 20. Once pregnant, she will pass some of these contaminants on to her child both in utero and through breast feeding. A recent National Academy of Sciences report recommends that females should limit exposure to dioxins until they are past childbearing age.
Why did the study not report a meals per month fish consumption recommendation for dioxins which were also found in farmed salmon at significant levels?
Dioxins are also included in EPAís fish consumption guidelines. But the authors of the study decided not to calculate EPA consumption recommendations for dioxins because EPA is in the process of reassessing its dioxin data. EPA may be changing its dioxin fish consumption advisory tables at some point in the future.
Arenít the EPA consumption guidelines tailored for people like fishermen who eat a lot of fish? Why would the average man on the street who doesnít eat much fish need to worry?
EPAís consumption advisories are not tailored for fishermen or others who typically eat a lot of fish. EPAís advisories were devised for the average individual. EPA does offer guidelines for modifying these standards for children who are more vulnerable to exposure to toxic contaminants and individuals who consume an above average amount of fish.
How was the study conducted?
A total of about 700 farmed and wild salmon (totaling about two metric tons) were collected from around the world: 459 whole farmed salmon were obtained from 51 salmon farms in eight different salmon producing regions; 144 salmon fillets were obtained from retail outlets in 16 cities in North America and Europe; and other suppliers provided 135 wild fish representing five wild species of Pacific salmon (chum, coho, chinook, pink, and sockeye). To get more accurate results about average contaminant levels, researchers individually tested composites made from three fish or three fillets for a total of 246 tested samples. Whole fish and fillets were composited by the location where they were produced or purchased. All samples were shipped to the analytical laboratory (AXYS Analytical in Sidney, British Columbia) fresh or frozen on ice or gel-packs. The fish were thawed and inspected by a fisheries biologist to verify species. Each fish was weighed, its length measured, and filleted to give two skin-on fillets. Skin-on fillets were analyzed because most salmon is sold at retail outlets with the skin on. In each case, the fillets from three fish were ground and re-ground together to make a single homogenous sample for analysis. Concentrations of dioxins and PCBs were measured using U.S. EPA methods, and similar procedures were used for toxaphene and dieldrin. The detection methods were based on gas chromatographic high resolution mass spectrometry. All instrument specifications and analytical methodologies for the study met standard EPA analytical methodologies.
There have been some reports of salmon farms treating their salmon with chemical coloring, veterinary drugs, and antibiotics. Did you look at these additives in farmed salmon?
This study did not analyze levels of colorants, drugs, and antibiotics in farmed salmon. Wild salmon develop their trademark pink flesh naturally by consuming tiny krill in the open ocean. Since farmed salmon donít consume large quantities of krill, their flesh is generally gray and is colored pink with the use of artificial colorings such as canthaxanthin or astaxanthin. Salmon farm operators also use veterinary drugs to control parasites and promote growth, and antibiotics to control infections. While the health and ecological effects of these substances are not fully understood, the overuse of antibiotics has been linked to bacterial resistance. And in 2002, the Scientific Committee on Animal Nutrition of the European Commission recommended that the amount of canthaxanthin permitted in salmon feed be reduced by two-thirds due to concerns about possible damage to the human retina.
How is this study related to the recent National Academy of Sciences study on dioxin in the food supply?
In July 2003, a National Academy of Sciences panel acknowledged excessive levels of dioxins and dioxin-like compounds in the food supply and recommended that steps be taken to reduce the publicís exposure to these contaminants. In a recommendation that closely paralleled the conclusions of the Science study on farmed salmon, the panel urged the government to give priority to reducing dioxins in animal feed including fishmeal. The Science study concluded that the high levels of contamination of farmed salmon were most likely related to contaminants in the fishmeal and fish oils that are fed to farmed salmon.
Are there other environmental problems associated with farmed salmon besides toxic contaminants?
Researchers have documented high levels of marine pollution coming from salmon farms due to the release of large quantities of waste, antibiotics, and other chemicals generated in salmon farming. Many analysts have discovered that, rather than helping to take pressure off of wild salmon stocks, salmon farms in fact harm wild stocks by spreading diseases and parasites to native salmon and when larger farmed salmon escape into the wild and out-compete wild salmon. Finally, the demand for fishmeal from salmon farms has contributed to the depletion of some fish stocks. Some experts have pointed out that because three pounds of wild fish for fishmeal are necessary to produce one pound of farmed salmon, current forms of salmon farming represent a highly inefficient use of the oceanís resources.