By Richard Sharpee, Ph.D., Science Manager, NOW Foods.
Polychlorinated biphenyls or PCBs, are a group of odorless and tasteless synthetic (man-made) organic chemicals that contain 209 possible individual chlorinated biphenyl compounds, called congeners (varieties). They exist in many chemical forms; oils, solids or vapors. Since there are no known natural sources of PCBs, all sources are related to commercial manufacture, use, storage and disposal. They are toxic industrial compounds that pose serious developmental health risks to the unborn, babies and children from prolonged or repeated exposure. These chemicals are harmful to adults as well and were classified in 1979 by the EPA as probable human carcinogens. Although they were banned from manufacture in the United States and in most of Europe at that time, it wasn’t until the Stockholm Convention Treaty of 2001 when intentional production of PCBs was banned worldwide. Even then, the treaty did not go into force until 2004 when 50 nations had ratified it. By May, 2009 most counties of the world (189/195) have ratified the treaty. However, during this time, the continued use of existing PCBs was not banned. Thus PCBs containing material is still in use today.
Source of PCBs
PCBs are also known by the trade name of Aroclor. These PCBs can be mixed in various combinations to yield different Aroclor mixtures that are chemically stable, nonflammable with high boiling points and electrical insulating properties. These properties made PCBs popular for a variety of industrial applications, including use in electrical transformers, hydraulic fluids, lubricants and carbonless paper. More than 1.5 billion pounds of PCBs were manufactured in the United States before they were banned in 1979, and some electrical equipment (e.g., transformers) in use today still contains PCBs with a life expectancy of 30 years or more.
PCBs are found everywhere in the environment; air, soil, sediments, water and animals. Unfortunately, the same properties that made PCBs ideal for industrial use make them slow to degrade (break down) in the environment. Most PCBs do not mix with water and instead settle into riverbeds, lake bottoms and coastal sediments where they can enter the food chain and accumulate in the bodies of fish, birds and mammals, including people. The types of PCBs likely to bioaccumulate in fish and bind to sediments are the most carcinogenic PCB mixtures.
Sources of PCB Exposure – Primarily Fish
Exposure to PCBs is predominately through diet, especially from fish and seafood products. However, red meat, eggs, and dairy products also may be important sources. Industrial and municipal discharges, agricultural practices, and storm water runoff can all deposit PCBs into the water where fish can absorb these directly from the water, suspended sediments, and their food. Since PCBs are slow to degrade, they are highly persistent in the environment with half-lives (time required for 50% of that compound to degrade by natural processes) in soil and sediment ranging from several months to greater than 20 years which can, in some cases, lead to accumulation at potentially dangerous levels. They are highly lipophilic (fat soluble) and can be rapidly accumulated by aquatic organisms. Through the aquatic food chain they can bioaccumulate in the fatty tissues of fish and other animals. Concentrations of PCBs can be from 2,000 times to more than a million times higher in aquatic animals than the concentrations found in surrounding waters. High-fat containing predatory fish such as shark, bluefish, king mackerel, swordfish, tilefish and Great Lakes salmon and lake trout have potentially the highest concentration. These high concentrations can pose potential health risks to people who frequently eat contaminated fish.
Based on available data on PCB concentrations in fish, the Environmental Defense Fund recommends limiting consumption of certain fish. In general, wild caught fish tend to have lower levels of PCBs. For example, 4 servings per month of wild Alaskan salmon are considered safe while 1 serving per month of farm raised salmon is the recommended safe consumption amount.
Although banned for many years, PCBs are found all over the world, with an increasing frequency of PCB-contaminated fish. For example in the US, the EPA’s National Listing of Fish and Wildlife Advisories increased 177% for PCBs between 1993 and 2003 with more than 39 states issuing advisories. Statewide freshwater advisories have been issued in several states while 7 states have issued coastal advisories for PCBs. Statewide advisories urge people to limit their consumption of all fish and shellfish from freshwater or coastal areas.
Health Risks Associated with Eating PCB-contaminated Fish
According to the EPA, contaminated fish are a persistent source of PCBs in the human diet. PCBs are readily absorbed through the gastrointestinal tract (75 to 90%) and distributed throughout the body. Because of their lipophilic (fat soluble) nature, they accumulate in body fat, liver and breast milk. PCBs are not highly toxic in a single dose (i.e., a single meal), but continued low levels of exposure (for example, eating contaminated fish over an extended period of time) may be harmful. Retention in body fat is linked to the degree of chlorination of the PCBs. Lower chlorinated PCBs have half-lives between 1 to 6 years while higher chlorinated PCBs have half-lives ranging from 8 to 24 years.
EPA rates PCBs as “probable human carcinogens,” since they cause cancer in laboratory animals. Other tests on laboratory animals show damage from PCBs to their circulatory, nervous, immune, endocrine and digestive systems. A number of studies indicate that PCBs may cause harm to the unborn and young children are especially susceptible to the effects of PCBs on their developing nervous systems. For example:
- Children of mothers who ate fish with large amounts of PCBs from the Great Lakes had smaller head size, reduced visual recognition and delayed muscle development.
- A mother’s exposure to PCBs and other chemicals was linked to the child’s birth weight, short-term memory, and learning disability.
- Older adults (49 to 86 years old) who ate fish containing PCBs and other contaminants had lower scores on several measures of memory and learning.
Reducing the Risk of Eating PCB-contaminated Seafood
Environmental Defense Fund suggests limiting consumption of certain fish and recommends proper cooking methods to help reduce your exposure:
- Before cooking, remove the skin, fat (along the back, sides and belly) and internal organs where toxins accumulate.
- When cooking, drain the fat away and avoid or reduce fish drippings.
- Grill or broil fish, frying seals in chemical pollutants that might be in the fish’s fat, while grilling or broiling allows fat to drain away.
- For smoked fish, fillet the fish and remove the skin before smoking.
Fish Oil Supplements – Safety
Nutritional supplements made from fish oil are growing more popular as consumers discover the health benefits of omega-3 fatty acids. Most dietary supplement companies take potential health risks from contaminated fish oil supplements seriously. These companies have implemented purification processes to reduce levels of environmental contaminants including PCBs. Most companies use processes such as molecular distillation and steam deodorization while other companies use absorbent technology. These technologies are designed to help remove contaminants such as PCBs. The processes use a combination of low pressure and high temperature or absorbent materials such as clay, silica and charcoal to separate PCBs from omega-3 fatty acids.
There are a variety of standards for allowable limits of contaminants in food (including dietary supplements). While allowable levels of PCBs vary greatly from the FDA’s standard of 2,000 parts per billion (ppb) in fish to the State of California’s uniquely stringent Proposition 65 limit at only 90 ppb, the most world-recognized standards are those of the USP/EC (United States Pharmacopeia / European Commission), which are based on WHO (World Health Organization) toxicity equivalents. These are safety based limits and are more stringent than the FDA limits for fish, but are substantially different than Prop 65 levels. The world-recognized PCB limit for consuming fish oil supplements are more than 20 times lower than the limits allowed for consuming fish. In other words, a single 8-ounce serving of fish is allowed to have 20 times more PCB exposure than a single 1000 mg fish oil capsule. And there are other contaminants present in fish at concentrations greater than fish oil supplements. Consequently, fish oil supplements represent a significantly safer source of omega-3 fatty acids when compared to fish.
Sources of Fish Oil Supplements
A number of different fish species are processed for fish oil. In general, fish oil for supplements comes primarily from fisheries in Norway, Peru and Chile and, to a lesser extent, Europe, Africa and the United States. These fisheries catch fish specifically to make fish oil and fish meal (which is used mostly in animal feed). Most fish caught are small species such as anchovies, sardines, mackerel and menhaden. These fish reproduce quickly, making them relatively resilient to fishing pressure, and thus a better choice when considering environmental impact. They also don’t live as long as some other species, reducing their lifetime exposure to and accumulation of environmental toxins such as PCBs.
Consuming fish oil supplements to obtain omega-3s is clearly preferable to eating those fish that Environmental Defense Fund rates as being the Worst Choice. Some of our Worst Choice fish, such as farmed Atlantic salmon, are fed large amounts of fishmeal and are raised in problematic environments.
Fish oil supplements from the better brands are adequately purified and safety tested. Consumers should take fish oil supplements from companies that meet the USP/EC standards that are based on accepted toxicity studies. In a survey conducted by Environmental Defense Fund, more than 80% (61 out of 75) of companies with fish oil supplements met the strictest U.S. standards for contaminants (those set by the EPA and the State of California Proposition 65).
In summary, most fish oil supplements appear to be adequately purified and safe. Consumers who take fish oil supplements should consider purchasing them from companies that verified they have met the strict USP/EC standards for contamination by PCBs.
Chlorination-the degree to which a substance contains chlorine. A highly chlorinated compound is high in chlorine content.
Molecular Distillation-a boiling process which separates products by size of the molecules.
Steam deodorization-heating with boiling water to remove the low molecular weight materials which are more likely to have bad odors.
Posted May 2, 2011.