Dioxins and Dioxin-Like Compounds
in the Food Supply

Strategies to Decrease Exposure 

Executive Summary & Introduction 

Food and Nutrition Board (FNB) / Institute of Medicine (IOM) / National Academies 1jul03

Dioxins and chemically-related compounds (referred to collectively as DLCs) occur as widespread, low-level contaminants in animal feeds and the human food supply. Because dioxins accumulate in fatty tissues, consumption of animal fats is thought to be the primary pathway for human exposure. In humans, dioxins are metabolized slowly and accumulate in body fat over a lifetime. Dioxin toxicity and its human health impact have been the subjects of recent reevaluations by the International Agency for Research on Cancer, the U.S. Agency for Toxic Substances and Disease Registry, the National Institute of Environmental Health Sciences, and the U.S. Environmental Protection Agency (EPA). Data indicate declining levels of dioxin in the environment and in human tissues, although the assessments prepared by the agencies differ and have not yet been reconciled.

Notwithstanding the declining overall levels, public concern about food safety issues such as endocrine disruptors in the food supply and the effects of dioxin-like compounds on children's health and development persists. Further, special populations that consume large amounts of fish and wildlife for cultural reasons (American Indian and Alaska Native tribes) and subsistence fishers have eating patterns that place them at higher risk for exposure levels that may be found to be dangerous.

Against this background, the National Science and Technology Council's Interagency Working Group (IWG) on Dioxin anticipated the need to develop policies to reduce dioxin exposure. IWG, with support from the U.S. Department of Agriculture (USDA), the U.S. Department of Health and Human Services, and other agencies and sponsors asked the National Academies to assist them by identifying potential strategies to meet this need.

The sponsors explicitly enjoined the committee from re-examining the question of whether low doses of dioxin are toxic or to what degree in general or specific populations. Separate scientific reviews have been initiated to reassess and reconcile the different exposure analyses. However, the sponsors anticipated that regulatory and other public health policies would likely be necessary to reduce exposures, especially among vulnerable populations, and foresaw the need to be prepared with evidence-based strategies.

The sponsors charged the Committee on the Implications of Dioxin in the Food Supply to review the scientific evidence to identify potential ways to reduce the levels of dioxin in food, taking into account the need to promote good nutrition and health. Specifically, the committee was charged to:

• Take into account the substantial body of data available in the EPA draft reassessment and other reports on the pathways by which DLCs add to the dioxin body burden by concentrating in food from sources such as animal feeds that contain recycled animal fat or sources contaminated by airborne DLCs, and through the intake of specific foods such as seafood, foods of animal origin (e.g., eggs, dairy products, meat) and plant foodstuffs

• Review the data on food-consumption patterns of various subgroups in the population that appear to be at increased risk due to physiological state, food practices, or geographic location

• Identify and describe possible risk-management options that could be instituted to decrease the content of dioxins in food animals, seafood, and other food products, and possible changes in food and/or nutrition policies that would decrease exposure, including, where possible, an assessment of the net risk reduction afforded by a risk management option, including effects on nutrition

• Identify and describe efforts in the United States and other countries to decrease dioxin exposures of specific subgroups of the population through public health or risk communication initiatives, and assess the extent to which federal food and nutrition policies contribute to decreasing exposure to dioxins.

The study sponsors recognized that the limited data available would likely allow only qualitative estimates of net risk, descriptions of exposure reduction, and identification of data needs. The committee did not make any judgments about the risks of human exposure of DLCs through food. Rather, it offered options available to the government to reduce this type of exposure and to increase benefits to nutrition and health, while gathering the data needed to determine future action.

The committee concluded that although direct health effects currently cannot be measured, animal and human epidemiological studies support exposure reduction while potential health risks are more fully studied. In its analysis, the committee developed and used a framework to identify and evaluate options to reduce exposure and suggested actions that the government might take as it continues to collect the data needed to devise a more comprehensive, long-term risk-management strategy.

This report is organized around three specific pathways that lead to DLC exposure through the food supply: (1) animal production systems, (2) human foods, and (3) food-consumption patterns.

DLCs enter the food chain when airborne contaminants that have been deposited on plants or in soil and sediment are taken up by food animals or fish (e.g., through grazing or the direct consumption of feeds that contain DLC-contaminated plant- and animal-based ingredients). Due to geographic variation in DLC levels that may result from long-distance air transport and deposition, naturally occurring and unintended contamination events, and different animal husbandry practices, the exposure of food animals to DLCs in forage and feed varies by region, by differences in DLC levels in feed ingredients, and by the combination of ingredients in different feeds. The resulting concentration of DLCs in food animals is a consequence of accumulated exposure from these various sources as the animals' body fat increases.

DLCs accumulate in human foods through the animal production systems pathway. Levels of exposure through foods may vary regionally, depending on the amount of locally produced food that is consumed. Most foods, except milk, are processed in bulk and distributed widely, so that foods purchased by consumers are less likely to reflect variable DLC levels. Thus, the exposure of the general population through the food supply appears to be relatively uniform. On the other hand, foods that are caught or harvested in the wild have levels of DLCs that reflect those found in the local environment, so some populations that rely on locally caught fish and wildlife for food may be at risk for higher exposure levels.

As a component of its data-gathering process, the committee commissioned an analysis of the population's DLC intake from foods at current levels of consumption. The analysis presented in this report was based on DLC values gathered in the FDA's Total Diet Study (a market basket survey) and linked to the Continuing Survey of Food Intakes by Individuals, which measures actual food intake. Dietary intake scenarios, based on the analysis, were used to predict the potential for reducing exposure to DLCs by decreasing meat and fish intake and by substituting low-fat (1 percent fat) or skim milk for whole (3.5 percent fat) milk. The scenarios indicated that the greatest exposure to DLCs through food was from animal fats found in meats, full-fat dairy products, and fatty fish.

The committee was charged by its sponsors to identify, evaluate, and recommend policy options to reduce dietary exposure to DLCs, while taking into consideration the need to maintain good nutrition and health. The committee was also charged to evaluate the net exposure reduction afforded by various risk-management options, including nutrition options, in light of efforts in the United States and abroad to decrease the exposure of sensitive or otherwise vulnerable populations.

The framework for risk-management options established a systematic approach to identify, evaluate, and recommend potential interventions to reduce the exposure of humans to DLCs through the food supply. The committee approached the development of options from the perspective of the three pathways discussed above and it considered the potential nutritional consequences of dietary modifications to reduce DLC exposure through risk-relationship analysis. For each option, the committee considered:

1. Alternate or interim actions

2. Current barriers to implementation

3. Anticipated DLC exposure reduction achievable through implementation

4. Risk relationships that included decreases (ancillary benefits) or increases (countervailing risks) in other risks.

The discussion of options to reduce DLC exposure through the food supply must consider food safety statutes and other regulatory policies and procedures that frame and constrain the adoption of exposure reduction options. Within the federal government, FDA has the primary food safety regulatory jurisdiction over DLCs in food. EPA considers food safety and acceptable levels of DLCs in fish when setting acceptable air and water emission levels for DLCs. FDA is the enforcement agency for DLCs in animal feed and human food, with the exception of meat and poultry, which are under the jurisdiction of USDA's Food Safety and Inspection Service (FSIS). FDA has broad authority to control DLCs in animal feed and human food, constrained by the requirement to make factual showings concerning DLCs and their risk in order to implement regulatory control.

The committee considered a range of possible interventions, but not all options were put forward as recommendations. Options considered to reduce DLC exposure through animal production systems included:

• Require testing for DLC levels in forage, feed, and feed ingredients,
• Establish tolerance levels for DLCs in forage, feed, and feed ingredients,
• Restrict the use of animal products, forage, feed, and feed ingredients that originate from specific areas that are considered to be contaminated, and
• Restrict the use of animal by-products in agriculture, animal husbandry, and manufacturing processes.

Options considered to reduce DLC exposure through the food supply included:

• Require testing and publishing of data on DLC levels in the human food supply, including food products, dietary supplements, and breast milk, to use in establishing tolerance levels in foods,
• Establish enforceable standards for DLC levels in processed foods and in packaging that comes in direct contact with food, and
• Require cleaning or washing practices for all vegetable, fruit, and grain crops that potentially had contact with soil.
• Increase the availability of low-fat and skim milk in federal feeding programs targeted to children, which currently favor the provision of whole milk (e.g., the National School Lunch Program),
• Establish a maximum saturated fat content for entrees in schools participating in federal child nutrition programs, and
• Promote changes in dietary-consumption patterns of the general population that more closely conform to recommendations to reduce consumption of animal fats, such as the recommendations of Dietary Guidelines for Americans.

Because of the persistent nature of DLCs and the uncertainty about their toxic effects, almost any action taken to reduce their concentration in the food supply will have a long-term, rather than an immediate, impact on human health. Such actions will, however, have an immediate impact on the food supply, which could, in turn, have other health and nutritional effects.

With regard to the possible detrimental nutritional effects due to changes in food-consumption patterns, the committee noted that current dietary recommendations for the general population stress the benefits of reduced intake of saturated fats to decrease the risk of many chronic diseases. Thus, changes in dietary patterns to reduce DLC exposure that involve a reduction of animal fats, the primary source of saturated fats in our diet, would generally have beneficial rather than detrimental nutritional effects.

Apart from the general population, the committee also took into account DLC-sensitive population groups, such as developing fetuses and infants, that are vulnerable due to developmental immaturity, and groups such as breastfeeding infants, subsistence fishers, and American Indian and Alaska Native fish-eating populations that receive higher-than-background levels of DLC exposure. Although not a highly exposed population, preadolescent and teenage girls and young women were of concern to the committee because they accumulate, over time, body burdens of DLCs that can, when they enter their child-bearing years, become a potential source of exposure for their developing infants in utero and while breastfeeding.

Recommendations to reduce exposure were tailored to the particular concerns of these groups, including weighing the benefits of breastfeeding against the risks of DLC exposure for infants, early intervention to reduce lifetime body burdens in children, especially girls, and cultural practices important to American Indian and Alaska Native tribes and other groups.

The committee considered both the scientific uncertainties in risk at current levels of exposure and the concern within the general population about exposure to DLCs. It further recognized that there are substantial gaps in the data that have to be filled before many of the identified policy options can be adopted. Based on the analysis of current data and deliberations concerning the strategic options available to the government, the committee recommended several risk-management actions. The committee's recommendations are qualitative rather than quantitative in light of the paucity of data to support specific reduction goals, and they fall into four categories: (1) general strategic recommendations, (2) high-priority risk-management interventions, (3) other risk-management interventions that deserve consideration, and (4) research and technology development to support risk management.

The following risk-management strategies were determined to be of greatest priority to achieve a reduction in human exposure to DLCs through the food supply:

• Strengthen interagency coordination for DLC risk management. The committee recommends that the sponsoring agencies empower an interagency coordination group with the authority and mandate to develop a risk-management strategy to reduce DLCs in the food supply.
• Interrupt the cycle of DLCs through forage, animal feed, and food-producing animals. The committee recommends that development of a risk-management strategy for DLCs give high-priority attention to reducing the contamination of animal forage and feed and interrupting the recycling of DLCs that result from the use of animal fat in animal feed.
• Reduce DLC intakes in girls and young women. The committee recommends that the government place a high public health priority on reducing DLC intakes by girls and young women in the years well before pregnancy is likely to occur.

The committee recommends that the government place a priority on the following research and technology development efforts:

• Develop cost-effective analytical methods and reevaluate the use of toxicity equivalents in assessing DLC exposure.
• Increase research efforts aimed at removing DLCs from animal forage and feed.
• Expand the National Health and Nutrition Examination Survey's data collection of DLC body burdens.
• Increase research efforts on the effects of dietary DLCs on fetuses and breastfeeding infants.
• Increase behavioral research on achieving dietary change.
• Develop predictive modeling tools and apply them in studies to assess the effects of potential interventions on reducing DLCs in the food supply.

Important progress has been made in reducing new discharges of DLCs into the environment. With respect to DLC exposure through food, most of the effort has focused on assessing the potential risks of DLCs. Given that the risk assessments conducted have raised concerns about the health impacts of DLCs and that there is no benefit, but possible harm, from DLC exposure through foods, the committee considers it appropriate for the federal government to focus its efforts on exposure reduction strategies. To move effectively toward reducing human exposure to DLCs through food, the federal government should begin by pursuing the following strategic courses of action: (1) establish an integrated risk-management strategy and action plan, (2) foster collaboration between the government and the private sector to reduce DLCs in the food supply, and (3) invest in the data required for effective risk management.

Considering the large number of federal agencies with responsibility for the safety of food, reduction of DLCs in the food supply will require action across the system. The committee recommends that, as an initial step, federal agencies including FDA, FSIS, and EPA, create an interagency coordination group to develop and implement a single, integrated risk-management strategy and action plan.

DLC exposure through food is a shared problem that requires shared, collaborative solutions. The committee recommends that as part of the process of developing an integrated riskmanagement strategy and action plan, the federal government create an atmosphere and program of collaboration with the private sector, involving agriculture, the food processing industry, health organizations, and consumers, which would include ongoing collection and re-evaluation of data.

There are significant gaps in the data required to devise, implement, and evaluate risk management interventions to reduce DLC exposure through food. The cost of analyzing DLC congeners is extremely high and often creates an impediment to effective data collection and analysis techniques. Research priority should be given to development of less costly analytical methods for determining the level of DLCs in animal feed and human food. The committee recommends that the development of a plan and a commitment of resources for data collection and analysis be a central element of the risk-management strategy and action plan for reducing DLC exposure through food.

Findings. Animal forage and feed are primary pathways for DLC contamination of the human food supply. This typically occurs by airborne deposition of DLCs on forage and plants used for animal feed. When animals consume contaminated forage and feed, DLCs are stored in their fat and subsequently enter the human food supply. In addition to plant material used as animal feed that may contain DLCs, several billion pounds of rendered animal fat are used annually as a feed ingredient, which serves to recycle DLCs and leads to the possibility of increasing levels of DLCs in meat and other animal-derived food products. The committee considers the animal forage, feed, and production stage of the food system to be a key leverage point for reducing DLC exposure through food because it is the primary point of entry of these compounds into the human food supply.

The committee recommends that the government's risk-management strategy for DLCs give high-priority attention to reducing the contamination of animal forage and feed and interrupting the recycling of DLCs that result from the use of animal fat in animal feed.

As an initial step, the government, in collaboration with the animal production and feed industries, should establish a nationwide data-collection effort and a single data repository on the levels of DLCs in animal forage and feed, which should be accessible for both public and private use. Government and industry should also begin collaboration immediately to define voluntary guidelines for good animal feeding and production practices that would reduce DLC levels in forage and feed and minimize other potential sources of DLC exposure during animal production.

The committee further recommends that the government, in collaboration with the animal production industry, identify means to achieve the reduction or elimination of DLC-containing animal fat as a component of animal feed. However, the committee recognizes that doing so could have unintended, negative consequences: (1) increased cost of food, (2) problems of unused animal fat disposal, (3) increased food spoilage, and (4) changes in the taste of food that consumers find unacceptable. The government should consider setting legally binding limits on DLCs in forage and feed only when more complete data are generated and a better understanding is developed of how DLC contamination can be avoided.

Fetuses and breastfeeding infants may be at particular risk from exposure to DLCs due to their potential to cause adverse neurodevelopmental, neurobehavioral, and immune system effects in developing systems, combined with the potential for exposure of breastfeeding infants to comparatively high levels of DLCs in breast milk. Data suggest that because DLCs accumulate in the body over time, waiting until pregnancy to reduce DLC intake has no significant impact on the mother's level or the baby's exposure in utero or through breastfeeding. Therefore, intervention to reduce DLCs must occur in the years well before pregnancy. Substituting low-fat or skim milk for whole milk, especially when coupled with other substitutions of foods lower in animal fat by girls and young women in the crucial years before pregnancy, could reduce DLC intakes and resulting levels of DLCs during pregnancy.

In order to reduce DLC body burdens in the future for women with childbearing potential, the committee recommends, as an immediate intervention, that the government take steps to increase the availability of foods low in animal fat in government-sponsored school breakfast and lunch programs and in child- and adult-care food programs. Specifically, the committee recommends that low-fat and skim milk be made readily available in the National School Lunch Program. In addition, the committee recommends that participants in the Special Supplemental Food Program for Women, Infants and Children be encouraged, except for children under 2 years of age, to choose low-fat or skim milk and low-fat versions of other animal-derived foods in their food packages. Further, to reduce other sources of animal fat, the committee recommends that USDA's Economic Research Service undertake a detailed analysis to determine the feasibility of and identify barriers to setting limits on the amount of saturated fat that should be allowed in animal-derived entree dishes in the National School Lunch and Breakfast Programs.

Although more data are needed, there are several other specific interventions that could be considered as part of an integrated risk-management strategy and action plan for reducing DLC exposure through food. These include: (1) reducing DLC-discharge sources in animal production areas, (2) removing DLC residues from food during processing, particularly by the removal of fat from meat products through trimming, (3) providing advisories and education to highly exposed populations, and (4) educating the general population about strategies for reducing exposure to DLCs.

Research and Technology Development to Support Risk Management

A broader research and technology agenda is needed to support risk-management efforts to reduce exposure to DLCs through food. Among many possible subjects for such efforts, the committee recommends that the government consider placing a priority on:

1. Development of low-cost analytical methods and a review of toxicity equivalents

2. Research to support the removal of DLCs from animal feed

3. Expansion of the National Health and Nutrition Examination Survey's data collection on DLC body burdens

4. Research on the effects of dietary DLCs on fetuses and breastfeeding infants

5. Behavioral research on achieving dietary change and, where feasible, predictive modeling studies on DLCs in the food supply.

Introduction

Dioxins and furans are unintentional contaminants that are released into the environment from combustion processes. The combustion of plant material from forest, brush, and range fires contributed to preindustrial deposition of dioxins into soil, sediment, and clay. Postindustrial sources are varied and include industrial burning (e.g., steel, coke, ceramic, and foundry), landfill fires, structural fires, utility pole and transformer storage yards, crematories, and backyard barrel burning of trash and woody and other plant material.

The geographic distribution of dioxins is a function of source and transport. The reservoir source of dioxins constitutes previous releases from combustion, soil deposition, volatolized and transported particulates, and soil run-off, which were sequestered and are now being rereleased into the environment. Thus, geographic distribution and accumulation of dioxins is not necessarily dependent upon a nearby source.

Dioxins and related compounds, including dioxin-like polychlorinated biphenyls (referred to collectively as DLCs), accumulate, through the food chain, into the lipid component of animal foods. However, levels of dioxins in the environment, and thus exposures to humans, have been declining since the late 1970s. Exposures, based on human tissue samples, decreased by about 75 percent between 1986 and 1996 (Papke, 1998). Even so, public concern persists with regard to the safety of the food supply and potential adverse outcomes to DLC exposure, especially in sensitive and highly exposed population groups. Sensitive groups within the general population include developing fetuses and infants. Highly exposed groups include breastfeeding infants, subsistence fishers, and American Indian and Alaska Native tribes for whom DLC-containing fish and wild game are important cultural food sources. These populations may be at increased risk not only from exposure to DLCs through certain foods, but also at nutritional risk if the availability of these foods is limited.

Although DLCs have been extensively studied as a contaminant, there is still a great deal of controversy regarding their potential for toxicity and the implications for human health. DLC exposure through foods occurs primarily by consumption of animal fats. However, many foods that are sources of DLCs are also sources of important nutrients, such as calcium and vitamin D in milk and cheese; protein, iron, and niacin in meats; protein, vitamin A, and iron in eggs; and omega-3 fatty acids in fish.

In order to evaluate and recommend risk management strategies to reduce DLC exposure through foods, consideration must be given to the potential impact of changes to food and nutrition policies, particularly those related to public education and food assistance programs, on the nutritional status and health of the population at large and to sensitive and highly exposed groups.

Following a request by federal agencies to the National Academies, an expert committee was appointed to review existing reports on the impact of DLCs on the safety of the food supply and to offer options to further reduce exposure to these contaminants, while considering the need to maintain health and optimize nutritional status, particularly with regard to sensitive and highly exposed groups. The Food and Nutrition Board, in consultation with the Board on Agriculture and Natural Resources and the Board on Environmental Studies and Toxicology, brought together an ad hoc committee to study the implications of DLCs in the food supply.

The charge to the committee was to: (1) take into account the substantial body of data available in the U.S. Environmental Protection Agency's draft reassessment (EPA, 2000) and other reports on the pathways by which DLCs add to the dioxin body burden by concentrating in foods from sources such as animal feed, and through intake of specific foods such as seafood, foods of animal origin (e.g., eggs, dairy products, meats) and plant foodstuffs; (2) review the data on food-consumption patterns of various subgroups of the population that appear to be at increased risk due to physiological state, food practices, or geographic location; (3) identify and describe possible risk management options that could be instituted to decrease the content of dioxins in food animals, seafood, and other food products, and possible changes in food and nutrition policies that would decrease exposure, including, where possible, an assessment of the net risk reduction afforded by a risk management option, including effects on nutrition; (4) estimate uncertainty in net risk and identify key data needs; if the uncertainty is too great due to a lack of data, provide a qualitative description of the potential for net risk reduction; (5) use existing estimates of dioxin risk as much as possible; adjust chemical risk estimates derived through upper bound method, if necessary, to allow comparison with nutrition benefits estimated using central tendency methods; and (6) identify and describe efforts in the United States and other countries to decrease dioxin exposures of specific subgroups of the population through public health or risk communication initiatives, and assess the extent to which federal food and nutrition policies contribute to decreasing exposure to dioxins.

The committee approached its charge by gathering information from existing literature and from workshop presentations by recognized experts (see Appendix C for workshop agendas), commissioning an analysis of DLC exposure through foods, deliberating on issues relevant to the task, and formulating an approach to address the scope of work. Reports and other data releases, such as the Centers for Disease Control and Prevention's Second National Report on Human Exposure to Environmental Chemicals (NCEH, 2003), occurred subsequent to the committee's deliberations. However, much of the information contained in these reports was provided, in part, to the committee by agency representatives at the open sessions of the committee meetings.

The committee developed an analytical framework to identify, evaluate, and formulate recommendations to reduce DLC exposure to the general population and to sensitive and highly exposed subgroups. This analytical framework, described in Chapter 6, organizes a wide array of policy options in the form of a matrix. Within the matrix, the committee developed a set of general categories that allowed it to array and analyze options and to ask detailed questions about each potential option that would help the committee recommend the most feasible interventions to reduce DLC exposure. This array of options is discussed in Chapter 7.

The committee's recommendations, which flow from the analytical framework, comprise those interventions that the committee determined would be both feasible and effective in reducing DLC exposure through the food supply, while not compromising good nutrition and health.

This report is organized into eight chapters that describe what is known about DLCs in agricultural and human food pathways and how DLCs move through the food chain from animal feeds to human food sources. Current evidence is used as a basis for recommended options to reduce exposure through the food supply. Chapters 2 and 3 summarize current evidence for health impacts and environmental sources of exposure to DLCs. Chapters 4 and 5 discuss issues of exposure through forage and feeds, human foods, and human food-consumption patterns. Chapter 6 presents the framework for developing policy options, and Chapter 7 discusses and summarizes the committee's deliberations on the array of options to reduce exposure. Chapter 8 provides a summary of the committee's findings, recommendations, and needs for future research.

The content of this report reflects the committee's fidelity to its charge. The committee utilized the available evidence as the basis of its deliberations and recommendations to reduce the impact of DLC exposure through the food supply. The separate issue of determining a safe or minimal level of exposure to DLCs, which was not part of the committee's charge, will be a challenge to address and requires much more research.

EPA (U.S. Environmental Protection Agency). 2000. Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds. Draft Final Report. Washington, DC: EPA.

NCEH (National Center for Environmental Health). 2003. Second National Report on Human Exposure to Environmental Chemicals. NCEH Publication No. 02-0716, Atlanta, GA: Centers for Disease Control and Prevention.

Papke O. 1998. PCDD/PCDF: Human background data for Germany, a 10-year experience, Environ Health Perspect 106:723-731.