Caption title. At head of title: Project summary. Distributed to depository libraries in microfiche. "June 1986." "EPA/600-S9-86-004."

Research on the class of compounds called dioxins began several decades ago, but the research activity increased substantially in the 1960's and 1970's, when the complex problem of dioxin contamination received national and international attention. Although considerable research has continued in this field, there are still voids in scientific knowledge, among them an understanding of the bioavailability of dioxins, that need to be identified to evaluate more accurately human and environmental risks associated with these chemicals. The EPA Office of Research and Development sponsored the Research Planning Workshop on the Bioavailability of Dioxins, September 9-12, 1984, that brought together scientists and managers in various aspects of dioxin work from government agencies, academia, and industry. About ninety researchers focused their attention during the four-day meeting on identifying the most obvious gaps in knowledge and the consequent research needs, evaluating the ongoing research on the bioavailability of chlorinated dioxins and related chemicals and developing a research plan. Workshop participants were organized into three groups that addressed the topics: environmental processes in bioavailability, bioavailability to ecosystems, and bioavailability to humans. The Environmental Processes in Bioavailability Group focused on defining various environmental processes controlling the bioavailability of TCDD in the biosphere. Transformation processes and bioavailability assessments were also discussed in this group. The Bioavailability in Ecosystems Group evaluated the factors relevant to the bioavailability of dioxins in aquatic and terrestrial ecosystems and the potential impact of these chemicals on ecosystems. Ecosystem processes were identified, particular species and communities that are potentially impacted by dioxins were addressed, and the role of food chains and the food web in human exposure and risks was discussed. The Bioavailability to Humans Group evaluated factors such as the bioavailability of TCDD from environmental matrices, the host factors affecting bioavailability, in vivo bioavailability, routes of exposure, toxic human effects, interspecies differences, and extrapolation from other animals to humans.