Polychlorinated biphenyls (PCBs) are a broad class of industrial chemicals once used extensively in electrical equipment, carbonless carbon paper and hydraulic fluids.   Prior to strict controls being placed on their use and disposal in the 1970s, large quantities were released into the environment. Because PCBs degrade slowly, trace levels can still be detected in many animals, including birds and fish.

The manufacture of PCBs was banned in 1979 in the U.S.   Subsequent investigation of occupational exposure and effects on rodents of exposure through food resulted in the current rigid safety standards. A study at Wayne State University in the mid-1980s that showed that babies born to women who consumed large amounts of PCB-contaminated fish from Lake Michigan had smaller head circumferences and lower birth weights was contested by other scientists at the time and have since been contradicted by other studies.

Despite the fact that workers exposed to PCBs in an industrial setting did not show an increased risk of cancer and that there have been no human studies that indicate a link between PCB exposure from fish and cancer, the US Food & Drug Administration (FDA) established tolerance levels for PCB trace residues in different types of food.   Products containing more than these tolerances are prohibited from the market. Tolerances are based on several factors, the most important being potential exposure over long periods of time and avoidability. The current FDA tolerance for PCBs in fish of 2,000 parts per billion (ppb) [or 2 parts per million (ppm)] was established in the early 1980s.

From the early 1970s until the early 1990s, most of the attention on PCBs in fish was focused on subsistence fish eaters and consumers of recreationally-caught fish that come from contaminated freshwater areas. As of 1993, PCBs in the total diet were less than one percent of levels in the early 1970s, falling from an average of 6.9 micrograms per day in 1971 to 0.05 micrograms per day between 1988 and 1990. More recent Environmental Protection Agency data indicates that PCBs levels in the environment have declined even further.

Commercial fish in the marketplace are well within the FDA tolerance level, and have been for more than a decade. FDA samples of both domestic and imported salmon in 1989 showed a mean parts-per-million (ppm) level of 0.39 in 1989, which fell to 0.21 in 1990 and again to 0.15 in 1991.

What you should know about PCB levels in salmon

Consumers' seafood eating habits have changed since the initial attention on PCBs. While per-capita consumption of seafood has risen slightly over the last decade, consumers' are eating a variety of fish from different parts of the country and around the world, thereby reducing their risk of PCB exposure from fish. Increased consumption of farmed species (shrimp, catfish, salmon and trout), reduction of lake and river production (less than 1% of the commercial seafood supply), and the composition of the tuna harvest have combined to reduce the public's general exposure to chemical residues through fish.

Further, exposure through consumption of beef is 15 times higher due to the amount consumed; likewise, exposure from fluid milk is 7 times higher than exposure from fish.   An examination of eight salmon in 2001 by the Suzuki foundation claimed that the farmed salmon showed higher levels of PCBs than the wild salmon. Publicity surrounding a program airing the study in the United Kingdom caused widespread panic among the salmon-eating public, and outrage among the salmon producers. The study was subsequently discredited because of its small sample size, and the BBC issued a public apology to the salmon farming industry.  

In 2003, the Environmental Working Group (EWG) issued an unpublished, non-peer reviewed report which was largely dismissed by the scientific community based on its small sample size (10 fish). Despite EWG's claims that farmed salmon were high in PCBs, the actual report showed that PCB levels in farmed salmon averaged one-one hundredth of FDA's tolerance level.

References

•  Fish Consumption and Reproductive Outcomes in Green Bay, Wisconsin, E. Dar, M.S.
Kanarek, H.A. Anderson and W.C. Sonzogni, Environmental Research 59, 189-201 (1992)

•  Centers for Disease Control, Agency for Toxic Substances and Disease Registry "Public
Health Statement for Polychlorinated Biphenyls (PCBs)"

•  Centers for Disease Control, Agency for Toxic Substances and Disease Registry
"ToxFAQs for Polychlorinated Biphenyls (PCBs)"

•  National Fisheries Institute, "Top Ten Seafoods"

•  U.S. Food & Drug Administration, "Findings of Total PCBs in Selected Fish Species, FY
1989-1991" Environmental Protection Agency, Draft Report on the Environment , Executive
Summary, p. iii

•  National Marine Fisheries Service, Fisheries of the United States, 2002 , p.3