Polychlorinated Biphenyls (PCB) are toxic chemicals that have pervaded the soil and waters.  PCBs are mixtures of synthetic and organic chemicals with the same chemical structure that are either found as oily liquids or waxy solids. PCBs were developed because they have very high burning temperatures and were used as fire retardants, insulators, and plasticizers in electrical devises mostly.  They are most often exposed to the environment through leaky equipment, illegal dumping, waste oil from electrical equipment, and hazardous waste.  The PCBs taint the soil and can run off into waters. Before 1977, approximately 1.5 billion pounds of PCBs were produced in the US.  The troubling health effects were discovered in workers using the PCBs and coming in close contact with them.  In 1976, Congress passed the Toxic Substances Control Act (TSCA), which banned the production of PCBs.  They are still prevalent, however, due to their existence in old electrical fixings and in their persistence in waste.  The EPA states that the composition of PCB mixtures actually changes when they are released into the environment.  The types that exist in soils and water today are more toxic than the PCBs workers were originally exposed to. 


The greatest risk for human exposure is through eating tainted fish.  Fish swim in waters polluted with PCBs and absorb the toxin.  It is accumulated in the fatty tissue of the fish.  The fish at greater risk are larger fish because they feed on smaller contaminated fish, in a process called bioaccumulation, and get higher PCB levels.  The most prevalent danger to PCB exposure today is through consuming farm raised salmon.  These farmed salmon are fed fish feed that is designed to be high in fish oil.  They are fed ground up fish, which have PCBs in their fatty tissue.  It is this fatty tissue that is most utilized in making high fish oil content.  Therefore, these farmed salmon ingest dangerous levels of PCBs and often make them unsafe to eat more than once in a month. 

The Pew Charitable Trust recently completed a report on the status of farmed salmon concerning dangerous PCB levels.  They tested the levels of farmed salmon against wild caught salmon.  The study team was made up of 6 researchers from various fields of the sciences; they bought and tested 2 metric tons of salmon.  The PCB levels in the farmed salmon averaged 5 times the safe EPA standards.  The EPA sets standards for food consumption based on a graduated scale, that matches content of contaminant with amount of consumption recommended.  They recommend only one meal per month with PCB levels between 25 and 48 parts per billion (ppb), and twice a week for levels of 4 to 6ppb, for instance.  The Pew study found levels that recommended eating farmed salmon only once a month.  They also found that on average farmed salmon had concentrations of health threatening contaminants 10 times higher than wild salmon, saying the farmed salmon was “consistently and significantly more concentrated”.

The Environmental Working Group also performed PCB tests on farmed salmon.  According to their findings, 70% of the farmed salmon tested were PCB contaminated and 90% of farmed salmon failed EPA health limits for weekly consumption, 6ppb, usually exceeding average by 4.5 times.  If this PCB level were found in salmon caught in the wild, then the EPA would restrict consumption to 1 time per month, but because they are bought not caught, consumption is not restricted. 

Most researchers believe that the reason for the high PCB contamination levels in the farmed salmon is due to their feed, which is ground up fish, similar to the problems that caused Mad Cow disease, because cows were ingesting ground up cow contaminated by their own feces.  In 3 independent studies (Jacobs 2002, Easton 2002, CFIA 1999) researchers tested 37 different fish feeds from 6 countries and found PCB contamination in every case.  PCBs builds up in salmon 20-30 times the levels of PCB build up in fish feed and environment (Jackson 2001) because of its lasting quality in its fatty tissue and the nature of bioaccumulation.  So low levels of contamination in fish feed can be representative of very dangerous levels in the farmed salmon.

The consumer can determine whether the salmon is farmed or not usually by asking the seller where the fish is from.  Though it is confusing because the seller may reply, “The Atlantic”, this means that the salmon is farmed, whereas “Pacific” or “Alaskan” salmon are wild.  The Pew report also found that American farmed salmon contained less PCBs than European farmed salmon, showing Scottish farmed salmon to be most contaminated and Denver farmed salmon to be least.  So knowing where the farming occurs can also determine risk levels. 


The EPA has found that PCBs negatively affect many different areas of the body and most of the major systems.  Perhaps most importantly, the EPA has found PCBs should be regarded as carcinogens.   Studies performed on animals have found definite correlation to conclude that PCBs cause cancer in animals, and the EPA calls PCBs “probable human carcinogens”.  Most often, they have found the effect of PCB exposure to result in liver cancer in humans. 

There have also been tests performed on Rhesus monkeys (who have very similar makeup to human beings) that showed many other ill effects of PCBs.  These tests have found weakening of the immune system and changes in the thyroid hormone levels that are concurrent with human symptoms due to high exposure.  The Rhesus monkey experiments also found reduction in birth weight, conception, and live birth rates from exposed mothers.  The effects of the PCB contamination was also long lasting, affecting childbirth much after exposure.  The same was true for human children born to mothers who were exposed to PCBs in their workplace.  Newborn monkeys who were exposed also showed neurological deficiencies in visual recognition, short-term memory, and learning.  


The regulation of PCB exposure is rather complicated due to the many ways exposure can occur.  Because the highest exposure comes through ingestion of contaminated fish, that is the most important part of regulation.  Any fish recreationally caught in the wild is regulated by the EPA, who use their graduated scale determining how often that fish is safe to eat, which was updated in 1999.  If the PCB level is higher than 48ppb, the EPA recommends never eating that fish.  As discussed earlier, studies have shown that most farmed salmon, the category of fish shown to have the highest contamination levels, have levels between 24 and 48ppb, which means that the EPA would recommend consumption only 1 time a month.  The EPA, however, does not regulate farmed salmon or commercially caught salmon, the FDA does.  The FDA’s standards are 500 times less protective than the EPA and have not been updated since 1984.  All the available data cannot sway their decision, however, because for the FDA to make a policy change, they must perform their own study, something 20 years overdue.  The FDA defends its refusal to administer stronger PCB standards because they contend that the high levels of helpful Omega-3 fatty acids in farmed salmon outweigh the negative effects of high PCB levels. 


Pew Charitable Trust Report. “Contaminants in Farmed Salmon” Science Magazine                          Jan: 2004 154-155


www.psr.org (Physicians for Social Responsibility)