PCB contamination and food safety

Background

Low levels of PCBs are found in the environment, and as as a result, in foods. The presence of these contaminants in foods and the environment means that everyone can be exposed to very low levels of PCBs. Exposure to these low levels does not appear to affect human health. However, PCBs can accumulate in the human body and remain there for years. PCBs stands for Polychlorinated Biphenyls. The name refers to any one, or any combination of 209 specific chemicals that are similar in structure. PCBs are extremely persistent. They last for many years because they do not break down easily on their own and they are difficult to destroy. PCBs were first manufactured in 1929. For several decades, they were used widely as ingredients in many industrial materials, such as sealing and caulking compounds, cutting oils, inks and paint additives. PCBs were also used to make coolants and lubricants for certain kinds of electrical equipment, such as transformers and capacitors. Attention began to focus on potential hazards linked to the use and disposal of PCBs, when the presence of PCBs was detected in lakes for the first time in 1966. By 1977, concern over the impact of PCBs on the environment led to a ban on manufacturing and importing PCBs. The ban did not cover PCBs that were already in use in electrical applications. These are being phased out now, and there are strict regulations for the handling, storage and disposal of PCBs. PCBs are mixtures of up to 209 individual synthetic chlorinated organic chemicals. Because PCBs are fire-resistant, stable, and do not conduct electricity, they were used in a wide range of industrial and consumer products. PCBs were widely used as a cooling fluid, fire retardant, and insulation in a many types of electrical equipment, as well as in such diverse applications as hydraulic and lubricating fluids, plastics, paints, and asphalts . Scientific concern about the safety of the use and disposal of PCBs began in the 1960s. In 1966 PCBs were detected in the Great Lakes. In 1968 PCBs were widely reported following discovery of PCB contamination in birds in Sweden and the poisoning of 1,200 people in Japan from consuming contaminated fish oil. In 1973 the Organization for Economic Cooperation and Development (OECD) recommended member nations to limit the use of PCBs, and develop approaches to limit human exposure. The environmental releases of PCBs worldwide, have resulted in traces of PCBs in our bodies. Because PCBs are persistent toxic substances that break down very slowly over time, PCBs accumulate in the food chain. Of particular concern is PCB accumulation in lakes and marine environments, where PCBs enter the waters through multiple pathways. Thus the primary sources of human environmental exposure to PCBs are through eating PCB-contaminated fish, meat, and dairy products; and breathing air contaminated with PCBs from old electrical equipment or nearby hazardous waste sites.

Where PCBs are Found Today

Trace levels of PCBs in the environment (air and water) are found all over the world. Some of this was caused by accidental releases and improper disposal practices in the past, but today, contamination is due primarily to the long-range transport of PCBs by global air currents. Once PCBs get into the environment, they accumulate in the cells of animals. The highest concentrations are found in animals at the top of the food chain, including humans. PCBs are still present in certain types of electrical equipment. Also, public concern over disposal practices has led to the storage of PCBs in many facilities around the country. In some instances, PCBs have been put into specially engineered landfills. Despite strict controls on the handling and storage of PCBs, there remains the potential for accidental releases into the environment.

How are we exposed to PCBs

Everyone is exposed to very small amounts of PCBs through food, and to a lesser extent, through air, soil and water. As a result, everyone has PCBs in their bodies. These low levels are unlikely to cause adverse health effects. Based on recent study, the average daily dietary intake of PCBs is thought to be less than half of one microgram (one microgram = one-millionth of a gram). People who eat large amounts of sports fish, wildlife or marine mammals may be exposed to higher dietary levels of PCBs. There is a risk of workplace exposure for people who replace or service old electrical equipment, and for those who transport PCBs to storage and destruction facilities or handle PCBs at these sites. Workers involved in these activities should wear protective clothing and follow prescribed decontamination procedures when they complete their work. People could also be exposed to PCBs through accidental releases, including uncontrolled fires involving PCBs. In these situations, several different things could happen:

• PCBs could be released in liquid form. They could then contaminate soil or water nearby;
• High temperatures in a fire could turn liquid PCBs into an aerosol form. If this happens, the PCBs could be inhaled. They could also be transported somewhere else by air currents; or
• When PCBs are burned at high temperatures, the process can turn them into different substances called dioxins and furans, which are far more toxic than PCBs.

Health Effects of PCBs

Most of what is known about the human health effects of PCBs is based on exposures due to accidental releases or job-related activities. These exposures are much higher than the levels normally found in the environment. The adverse health effects include a severe form of acne (chloracne), swelling of the upper eyelids, discolouring of the nails and skin, numbness in the arms and/or legs, weakness, muscle spasms, chronic bronchitis, and problems related to the nervous system. The current state of knowledge suggests that low-level exposures to PCBs are unlikely to cause adverse health effects. People eating large amounts of certain sports fish, wild game and marine mammals are at increased risk for higher exposures and possible adverse health effects. People at greater risk include Aboriginal peoples, as well as anglers and hunters and their families. Some studies dealing with long-term low-level exposures to PCBs suggest subtle effects on reproduction and on the development of newborns and young children. Research into this subject continues. The issues are very complex because the chemical make-up of PCBs mixtures varies from one exposure situation to the next, and people exposed to PCBs may have been exposed to other related contaminants at the same time. Scientists must determine the role each substance may play in causing adverse health effects. The most commonly observed health effects in people exposed to high levels (i.e., occupational exposures) of PCBs are skin conditions such as acne and rashes. Studies in exposed workers have shown changes in blood and urine, which may indicate liver damage. PCB is also considered a probable human carcinogen, based on limited evidence that long-term, high-level occupational exposure can lead to increased incidence of liver and kidney cancers . PCB exposures in the general population are not likely to result in skin and liver effects.There is more uncertainty about the effects of chronic PCB exposure to levels typically associated with environmental exposures. Human health studies indicate that PCBs:

• May affect women’s reproductive functions
• May expose fetuses and newborns through the placenta and breastfeeding
• May create neurobehavioral and developmental deficits in newborns and children exposed to PCBs in utero (passed from the mother’s PCB body burden to the fetus through the placenta), including:
  • Low birth weight
  • Shorter gestational period
  • Smaller head size
  • Abnormal neurodevelopment (e.g., abnormal reflexes, motor immaturity, permanent learning disabilities, mental retardation, impaired cognitive skills, problems with memory, and depressed responsiveness)
  • Neurobehavioral deficits (e.g., increased hyperactivity)
  • Immunologic effects (e.g., allergic reactions, higher prevalence of recurrent middle ear infections, and higher prevalence of chicken pox)
  • Problems with thyroid function
• May decrease thyroid hormone levels
• May weaken the immune system
• May increase cancer risks, such as liver and non-Hodgkin’s lymphoma (NHL)
• May produce a number of other negative health effects from chronic exposures, including:
  • Hypertension and related cardiovascular effects
  • Respiratory tract symptoms (e.g., cough, and chest tightness)
  • Gastrointestinal effects (e.g., nausea, vomiting, and abdominal pain)
  • Eye irritation.

Minimizing Your Risk

To minimize your risk of exposure and health effects related to PCBs:

• Follow advice about limiting your consumption of wild game and sports fish. In addition, you can prepare game and sports fish in a way that minimizes your exposure to PCBs. Discard the inner organs and remove the skin and all visible fat. Broil, bake, boil or grill the flesh, but avoid frying as this cooking method retains the fat;
• There is no need to restrict consumption of fish from the commercial food supply (e.g., fish bought in a supermarket);
• Never burn wood that has been treated or painted, since burning materials that contain PCBs can create dioxins and furans; and
• If you are at risk for exposure to PCBs in the workplace, be sure to take appropriate safety precautions and follow all prescribed decontamination procedures.