Fate and Transport in the Environment
Methods for Monitoring in the Environment
Methods for Measuring Human Exposure
Strategies for Preventing or Controlling Exposure
PCBs - Harmful Effects
PCBs - Dose Response
Sites of Toxicity
Mechanisms of Toxicity
Links for More Information
Who is exposed?
Although the manufacturing of PCBs was discontinued in 1977, exposure to these chemicals still persists due to their ability to circulate between various media and locations and their inefficient breakdown in the environment. PCBs can enter the air, water, or soil from their manufacture, leaks, fires, disposal or transport. When PCBs contaminate the water, they can bioaccumulate in the fish. Their bioaccumulation in fish is of concern to public health because the primary route of human exposure to PCBs is through eating these contaminated fish. Several epidemiologic studies have reported associations between fish consumption and adverse health effects attributable to PCBs.
Populations that are particularly at risk of PCB exposure include people with high fish consumption (Native Americans and sport anglers), the elderly, pregnant women, fetuses and nursing infants of mothers who consume contaminated Great Lakes fish, and people living near hazardous waste sites. Because PCBs bioaccumulate in the fat, body burden appears to be associated with increased fish consumption. It is estimated that people who eat sportfish consume 2-3 times more fish than the overall U.S. population and that those who eat Great Lakes sportfish for more than 15 years have 2-4 times more pollutants in their serum than nonfisheaters.
Although PCBs persistent in the environment, there are several steps people can take to reduce their exposure to these hazardous chemicals.
- Pay attention and obey state and tribal fish advisories.
- Discourage children from playing with old appliances, electrical equipment, or transformers.
- Discourage children from playing around or in dirt near hazardous waste sites.
- If working with PCBs at the workplace, wash potentially contaminated clothing separately and if possible, shower and change clothes before leaving work.
In the 1970s, commercial production of PCBs in the United States was restricted, and ended in 1979. Because of the ban on PCB production, decreasing use of PCBs, and efforts to remediate contaminated sites, general population exposure to PCBs in fish and other foods has been significantly reduced, and PCB levels in human blood are also decreasing. The EPA web site http://www.epa.gov/pcb provides information on numerous laws and regulations regarding PCBs as well as rules for their handling, storage, disposal, and decontamination procedures. The following list outlines some of the more specific restrictions placed on PCBs. Although it is by no means conclusive, it highlights those pertaining specifically to exposure prevention.
- Polychlorinated biphenyls (PCBs) have been identified in at least 500 of the 1,598 hazardous waste sites that have been proposed for inclusion on the EPA National Priorities List (NPL).
- The Federal Registry and its amendments include requirements for the manufacture, processing, distributing in commerce, use, cleanup, storage, and disposal of PCBs.
- EPA requires that companies that transport, store, or dispose of PCBs follow the rules and regulations of the federal hazardous waste management program. EPA also limits the amount of PCBs put into publicly owned waste water treatment plants. EPA requires that industry tell the National Response Center each time 1 pound or more of PCBs have been released to the environment.
- The Toxic Substances Control Act (TSCA) bans manufacturing, processing, and distributing PCBs in commerce.
- The Toxic Substances Control Act also regulates any release of PCBs into the environment, including accidental leaks or spills. Specific actions are required depending upon the concentration of PCBs in soil resulting from spills. The PCB Spill Cleanup Policy is the source of risk-based PCB "cleanup levels" for unrestricted versus restricted areas (i.e., areas that are easily accessible by the general public, versus sites that are remote or difficult to access) that have been applied to the remediation of contaminated sites under other federal programs.
- In April 1996, President Clinton partially lifted the ban on PCB imports, enabling PCB waste to be shipped to the United States for incineration. Canada responded in November 1996 with an extension of an export ban to prevent the export of PCB waste from Canada, reflecting the evolving competition for hazardous waste business.
- OSHA regulates that workers not be exposed by inhalation over a period of 8 hours for 5 days per week to more than 1 milligram per cubic meter of air (mg/m_) for 42% chlorine PCBs, or to 0.5 mg/m_ for 54% chlorine PCBs.
- OSHA requires employers of workers who are occupationally exposed to PCBs to institute engineering controls and work practices to reduce and maintain employee exposure at or below permissible exposure limits (PELs). Respirators must be provided and used during the time period necessary to install or implement feasible engineering and work practice controls.
- NIOSH recommends that workers not breathe air containing 42 or 54% chlorine PCB levels higher than 1 microgram per cubic meter of air (µg/m_) for a 10-hour workday, 40-hour workweek.
- The FDA has set residue limits for PCBs in various foods to protect from harmful health effects. FDA required limits include 0.2 parts of PCBs per million parts (ppm) in infant and junior foods, 0.3 ppm in eggs, 1.5 ppm in milk and other dairy products (fat basis), 2 ppm in fish and shellfish (edible portions), and 3 ppm in poultry and red meat (fat basis).
- The EPA standard for PCBs in drinking water is 0.5 parts of PCBs per billion parts (ppb) of water. For the protection of human health from the possible effects of drinking the water or eating the fish or shellfish from lakes and streams that are contaminated with PCBs, the EPA regulates that the level of PCBs in these waters be no greater than 0.17 parts of PCBs per trillion parts (ppt) of water. Many individual states have also established more stringent drinking water standards and guidelines.
- Currently, 679 advisories restricting the consumption of PCB-contaminated fish, shellfish, and wildlife have been issued in 37 states and in one U.S. Territory (American Samoa).
Are PCBs a real threat to the health of the endocrine system?
Although epidemiologic studies have not always produced consistent results regarding the effects of PCBs on the endocrine system, there has certainly been enough evidence gathered to warrant further investigation. Evidence of PCBs toxicity to the reproductive system and the thyroid gland has been demonstrated in human studies and more strongly in animal studies. While some may argue that endocrine disrupting chemicals including PCBs are not a significant public health threat, there is a wealth of information available to at least demonstrate the potential for adverse health outcomes that cannot be ignored given the vital role of the endocrine system to human health and development. PCBs in particular are very prevalent in the environment. Studies in the general population have detected PCBs in blood, adipose tissue, breast milk, and other tissue samples indicating widespread exposure to PCBs. Figure 1 below illustrates the frequency of NPL sites with PCB contamination.
Figure 1. Frequency of NPL sites with PCB contamination
It has been difficult to determine minimal risk levels of PCBs because people are generally environmentally exposed to PCB mixtures of different congeneric composition than commercial PCB mixtures. It is possible that environmental PCB mixures may be more or less toxic than commercial mixtures. One method that has been used to estimate risk is the toxic equivalency factor (TEF) method. This method compares the toxicity of individual PCB congeners to the structurally similar 2,3,7,8-TCDD (dioxin), which is known to be more toxic and has been extensively studied. The primary limitation to this method is that it assumes a common mechanism of action that involves an Ah-receptor mechanism of toxicity.
Despite uncertainties in the data, concern over the adverse health effects of PCB exposure has prompted health officials, government agencies, and environmental groups to initiate and maintain efforts to control exposure to PCBs through regulations, fish advisories and other recommendations to the public. Furthermore, the information available on PCBs health effects to the endocrine system has also been persuasive enough to convince researchers to initiate more investigations on the reproductive toxicity, dose-response, and genotoxicity of PCBs. While gathering more information on the adverse health effects of PCBs will help to refine our current state of knowledge, it will also aid in public health decision making. In the meantime, enough scientific information is available to suggest that PCBs are a credible threat to the endocrine system, particularly for individuals in high-risk categories such as people with high fish consumption (Native Americans and sport anglers), the elderly, pregnant women, fetuses and nursing infants of mothers who consume contaminated Great Lakes fish, and people living near hazardous waste sites.
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