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1 Introduction BACKGROUND 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 indus- trial 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, geo- graphic distribution and accumulation of dioxins is not necessarily dependent upon a nearby source. Dioxins and related compounds, including dioxin-like polychlorinated bi- phenyls (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, 19981. 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. 13
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4 DIOXINS AND DIOXIN-LIKE COMPOUNDS IN THE FOOD SUPPLY 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 implica- tions for human health. DLC exposure through foods occurs primarily by con- sumption 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. THE COMMITTEE AND ITS CHARGE Following a request by federal agencies to the National Academies, an ex- pert 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 reas- sessment (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
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INTRODUCTION 15 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 pos- sible; 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 popula- tion through public health or risk communication initiatives, and assess the extent to which federal food and nutrition policies contribute to decreasing exposure to 1- . aloxlns. 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 Expo- sure 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, de- scribed 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 fea- sible interventions to reduce DLC exposure. This array of options is discussed in Chapter 7. The committee's recommendations, which flow from the analytical frame- work, 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. ORGANIZATION OF THE REPORT 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 evi- dence 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
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16 DIOXINS AND DIOXIN-LIKE COMPOUNDS IN THE FOOD SUPPLY Chapter 7 discusses and summarizes the comm~ttee's deliberations on the array of options to reduce exposure. Chapter 8 provides a summary of the comm~ttee'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 sup- ply. The separate issue of determining a safe or minimal level of exposure to DLCs, which was not part of the comm~ttee's charge, will be a challenge to address and requires much more research. REFERENCES 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 Expo- sure 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.