Health Risks From Dioxin And Related Compounds

Although the U.S. Environmental Protection Agency presented a comprehensive review of the scientific literature in its 2003 draft reassessment of the risks of dioxin, the agency did not sufficiently quantify the uncertainties and variabilities associated with the risks, nor did it adequately justify the assumptions used to estimate them, according to this new report from the National Academies' National Research Council. The committee that wrote the report recommended that EPA re-estimate the risks using several different assumptions and better communicate the uncertainties in those estimates. The agency also should explain more clearly how it selects both the data upon which the reassessment is based and the methods used to analyze them.

Some dioxins, which are chemical compounds that share certain structural and biological characteristics, have been linked to adverse human health effects, including cancer. 1 Often the byproducts of combustion and industrial processes, complex mixtures of dioxins enter the food chain and human diet through emissions into the air that settle on soil, plants, and water. The Environmental Protection Agency (EPA) and other entities, such as the World Health Organization, began assessing the potential human health risks of dioxins in the 1970s, when animal studies on one of them 2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD showed it to be the most potent cancer-causing chemical studied to date. EPAs initial assessment of dioxins was published in 1985. Since that time, there have been major advances in the scientific understanding of dioxin toxicity and significant new studies on dioxins potential adverse health effects. As a result, in 1991 EPA decided to conduct a reassessment of the health risks of exposure to dioxins. A draft of this reassessment was reviewed by a scientific peer review panel in 1995, and three panels reviewed key segments of later drafts in 1997 and 2000.

Increasing international concern is being expressed regarding the contamination of the environment with polychlorinated dibenzo-p dioxins (PCDDs) and polychlorinated dibenzofurans because certain of these chemicals have been shown to be highly toxic to animals and are ubiquitous in the environment. They are known to be distributed as contaminants of commercial products and as by-products from com bustion processes. A considerable volume of information has accumulated on these chemicals in the past two decades, particularly for the most toxic of them, 2,3,7,8-tetrach1orodibenzo-p-dioxin (2,3,7,8-TCDD). However, this body of knowledge has not succeeded in resolving genuine judgmental differences among experts in the field as to the degree of hazard to human health and the environment. In light of the widespread public concern, it is clearly imperative to come to grips with the continuing scientific controversy, to review the data, assess the issues, to see where areas of agreement exist, and where further research is needed to resolve remaining areas of disagree ment. This volume represents an effort to contribute to these goals.

Dioxin and dioxin-like compounds, or DLCs, are found throughout the environment, in soil, water, and air. People are exposed to these unintentional environmental contaminants primarily through the food supply, although at low levels, particularly by eating animal fat in meat, dairy products, and fish. While the amount of DLCs in the environment has declined since the late 1970s, the public continues to be concerned about the safety of the food supply and the potential adverse health effects of DLC exposure, especially in groups such as developing fetuses and infants, who are more sensitive to the toxic effects of these compounds. Dioxins and Dioxin-like Compounds in the Food Supply: Strategies to Decrease Exposure, recommends policy options to reduce exposure to these contaminants while considering how implementing these options could both reduce health risks and affect nutrition, particularly in sensitive and highly exposed groups, if dietary changes are suggested.

This book originated in a series of cross-disciplinary conversations in the years 1984-1990 between the editor, who is a physician-researcher involved in clinical and laboratory research, and a dioxin toxicologist. During the years in which the conversations took place, an extraordinary amount of new scientific literature was published related to dioxins, defined for purposes of this text as the chlorinated dibenzo-p-dioxins, dibenzofurans, polychlorinated biphe nyls (PCB's) and other compounds that are structurally and toxicologically similar to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7 ,8-TCDD), the most extensively studied and most toxic of this group of chemicals. Dioxins also began to interest not only chemists and toxicologists, but also specialists from diverse disciplines such as wildlife and environmental science, immunology, neuroscience,public health, epidemiology, med icine, government, law, sociology, and journalism. Specialists from such varied disciplines, while familiar with their own literature, frequently did not have time to follow the dioxin literature outside their specialty area. In addition, each specialty had unique knowledge, methods, and perspectives. Cross disciplinary conversation was necessary, but all too frequently, specialists from the various disciplines did not speak the same language, resulting in misunderstanding.

This volume is a tribute to Professor Otto Hutzinger, the founding editor of The Handbook of Environmental Chemistry, in recognition of his pioneering work and contribution to our understanding of the sources, fate, exposure and effects of persistent organic pollutants. It consists of fourteen chapters written by individuals who have been inspired by his work and have followed in his footsteps by refining our knowledge of this field and opening new research directions. In Professor Hutzinger’s tradition of passing on valuable information to others, the authors present recent advances in areas such as inventories, remediation, and analytical determinations. Levels and trends in abiotic environments, biota, and human exposure via food, as well as the risks to the environment and humans from polychlorinated dibenzo dioxins, furans, and PCBs are also discussed. Other chapters deal with the relevant topics of DDT and its metabolites along with halogenated and phosphorus flame retardants.