You may have heard some dirt on dioxins, but now it is time to dig deeper. Just what are dioxins and what should consumers know about them? Dioxins are a family of chemical compounds with common chemical structures and biological characteristics. There have been concerns over the years about the potential health impact of dioxins found in the environment and in the food supply. In recent decades these concerns have prompted significant coordinated U.S. government regulatory and industry efforts to reduce dioxin emissions to the environment. The results are impressive. According to Environmental Protection Agency (EPA) data, dioxin emissions from quantified sources have dropped by over 90 percent since 1987.
Dioxins are colorless, odorless organic compounds containing carbon, hydrogen, oxygen, and chlorine. They occur naturally in small quantities as a result of volcanic activity, brush and forest fires, and are also generated by human activities such as chemical manufacturing and incineration. Backyard trash burning, a common practice in rural areas, is the number one quantifiable source of dioxins to the environment today. EPA defines backyard trash burning as the burning of household trash by residents on their own property. Trash typically burned can include paper, cardboard, food scraps, plastics, and yard trimmings—essentially any materials that would otherwise be recycled or sent to a landfill.
Exposure to Dioxins
Dioxins can be deposited on plants and taken up and concentrated by animals and fish as they feed. This is how dioxins enter the food chain. It is estimated that 95 percent of human exposure to dioxins comes from the diet through food and human breast milk as dioxins have a high affinity for fatty substances and are found in fat tissue.
Dioxins are usually detected at concentrations in the part-per-trillion (ppt) range. (One part-per-trillion is roughly equivalent to a drop of ink in an Olympic size swimming pool.)
Dioxins, Diet, and Health
Dioxins have been the subject of intensive scientific research and environmental controls since the 1970s. In July 2006 the National Research Council (NRC) of the National Academies published a report evaluating a previous review of the scientific literature and a draft assessment of the health risks of dioxin conducted by the Environmental Protection Agency (EPA) in 2003. According to the NRC, the previous risk assessment did not adequately quantify the uncertainties associated with the risks, nor did it adequately justify the assumptions used to estimate the risks. The use of different and more scientifically supportable assumptions may result in a lower estimated cancer risk for humans exposed to low doses of dioxin and related compounds. In other words, the 2003 risk assessment may have over estimated the cancer risks associated with the low levels of exposure experienced by most people and animals.
Although the NRC review committee did not go so far as to suggest that there is a lower cancer risk to humans through exposure to dioxins in food, water, or the environment, it gave no reason for increased concern. Committee Chair David L. Eaton, a professor and associate vice provost for research at the University of Washington, Seattle, noted the significant decline in the levels of dioxins from emissions since 1987. The Committee urged EPA to follow the Committee’s recommendations to revise the 2003 assessment.
Typical dietary exposure has not resulted in elevated levels of dioxin in the body. The level of dietary exposure, even over the course of many years, is still far below that which might occur in accidental occupational exposures. Scientists continue to study any potential health risks although there appears to be no clearly established health effects associated with exposure to the current low levels of dioxins in food or the environment. Chloracne, a reversible skin condition, has been documented in people who are accidentally exposed to much higher levels of dioxin in industrial settings, or who are intentionally poisoned.
Dioxins are known to pass from the mother’s body to the infant during breastfeeding. Because dioxins can be found in human breast milk, some have questioned whether it is safe for infants to nurse. Many health experts recognize that breast-feeding provides numerous nutritional, immunological, and other benefits to infants in the first months of life.
Scientists continue to study dioxins to ensure there is no harm to humans through dietary exposure, and industry and government continue their efforts to reduce dioxin levels in the environment.
Minimizing Dietary Exposure to Dioxins
Choosing a balanced diet that is low in total fat helps consumers minimize potential exposure to dioxin from food because dioxins are found mostly in animal fats (due to the fat-soluble properties of the dioxin compound). Adherence to the recommendations of the 2005 Dietary Guidelines for Americans should result in reduced dioxin exposure.
These guidelines include the recommendations to
- Choose leaner cuts of beef, pork, and poultry; and trim the fat and remove the skin from chicken before cooking
- Choose non-fat and low-fat milk and milk products
These strategies help lower the intake of total fats—measures that make sense for overall health reasons: they therefore also help reduce the risk of exposure to dioxins.
Consumers are not advised to eliminate any one food or food group in an effort to reduce exposure to dioxins. Eliminating foods or food groups could lead to nutrient inadequacies and significant health consequences because each food group provides at least one nutrient important for health. In other words, no food or food groups, including breast-feeding, need be eliminated in an effort to reduce potential exposure to dioxins because the benefits of food nutrients outweigh the risks of dioxin exposure.
U.S. Efforts to Reduce Dioxins in the Environment
Major reductions in industrial sources of dioxins have led to significant decreases in the levels of dioxins in the environment, and thus to decreased levels of dioxins found in the food chain. Since the mid-1990s, dioxin levels in meat and poultry have declined significantly. Also, a recent study by the Centers for Disease Control and Prevention (CDC) confirms that dioxin levels in human tissues are very low and that the levels of dioxins in human blood have decreased by more than 80 percent since the 1980s. However, it is important to note that humans will always be exposed to some low levels of dioxins because of the naturally occurring sources of these compounds such as forest fires and volcanic activity (Figure 2 below).
| Figure 1: Dioxin in Emissions (TEQ=Toxicity Equivalent) |
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| Figure 2: Trends in Dioxin Levels in Lake Sediment, Archived Food, and Human Tissue |
| Note: Click on image to view larger version.
Source: Based on Hagenmeier and Walczok (1996), Ferrario et al., (1998) and Lorber (2002) |
Federal Government Efforts to Minimize Dioxin Levels in Foods
In 1999, the U.S. Food and Drug Administration’s (FDA) Center for Food Safety and Applied Nutrition (CFSAN) began annual monitoring for dioxin in foods collected in its Total Diet Study (TDS), a yearly program that determines levels of various contaminants and nutrients in food. TDS analyses are used to determine human exposure levels; if increased dioxin sources are detected, the FDA removes the source. The TDS indicates that dietary intake levels of dioxins compounds are 90 percent lower than those in the 1970s and 50 percent lower than those in the mid-1990s.
In May 2000, FDA’s Center for Veterinary Medicine (CVM) initiated a preliminary national survey of dioxin-like compounds in animal fats and feed. The purpose of this survey was to determine background levels of dioxins compounds in ingredients commonly used in animal feeds. In addition to reducing environmental levels and monitoring foods, the government is continuing research efforts to better understand how dioxins get into the food supply and to identify ways to further reduce the level of dioxins in food.
The U.S. Department of Agriculture’s Food Safety and Inspection Service periodically monitors the levels of dioxin compounds in various livestock and has also noted that levels of these compounds have declined in all livestock surveyed.
Bottom Line
Humans always have been and always will be exposed to some low level of dioxins because of their natural environmental sources. To date, however, there have been no established health effects in people resulting from typical dioxin exposure through food. Americans should continue to follow the dietary recommendations outlined in the 2005 Dietary Guidelines for Americans.
The federal government, regulators, educators, and physicians can all agree that a well balanced diet, rich in a variety of fruits, vegetables, and grains and enjoyed in moderation, is key to a healthful lifestyle.
Other Resources
Centers for Disease Control and Prevention
Third National Report on Human Exposure to Environmental Chemicals:
www.cdc.gov/exposurereport
Dietary Guidelines for Americans, Sixth Edition (2005)
US Department of Health and Human Services
http://www.health.gov/dietaryguidelines/
The National Academies, National Research Council
Health Risks from Dioxin and Related Compounds: Evaluation of the EPA Reassessment
http://www.nap.edu/catalog/11688.html
U.S. Department of Agriculture
http://www.cnpp.usda.gov/DG2005/index.html
U.S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
Interagency Working Group on Dioxin
Questions and Answers about Dioxins, October 2004
http://www.cfsan.fda.gov/~lrd/dioxinqa.html
U.S. Environmental Protection Agency
National Center for Environmental Assessment
Dioxin and Related Compounds
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=55264
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