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Inventory of Dioxin Sources and Environmental Releases

EPA released the dioxin inventory of sources in the form of a final report entitled, "An inventory of sources and environmental releases of dioxin-like compounds in the United States for the years 1987, 1995 and 2000" in November 2006. This report represented an evaluation of sources and emissions of dioxins (CDDs), dibenzofurans (CDFs) and coplanar PCBs to the air, land and water of the U.S. The report contained an inventory that suggested there was a significant reduction in environmental releases of dioxin-like compounds from regulated industrial sources between the years 1987 and 2000, and that the open burning of residential refuse in backyard burn barrels was the largest source in 2000 that could be reliably quantified. EPA has been working on a revised version of the report. An external review draft was released in 2013 and is undergoing a public peer review before the final report will be released on the EPA web site.

Background

The purpose of this report was to present a comprehensive inventory and overview of sources and environmental releases of dioxin-like compounds in the United States. The major identified sources of environmental releases of dioxin-like compounds are grouped into six broad categories: combustion sources, metals smelting, refining and process sources, chemical manufacturing sources, natural sources, and environmental reservoirs. Estimates of annual releases to land, air, and water are presented for each source category and summarized for reference years 1987, 1995, and 2000. The quantitative results are expressed in terms of the toxicity equivalent (TEQ) of the mixture of polychlorinated dibenzo-p-dioxin (CDD) and polychlorinated dibenzofuran (CDF) compounds present in environmental releases using a procedure sanctioned by the World Health Organization (WHO) in 1998. This TEQ procedure translates the complex mixture of CDDs and CDFs characteristic of environmental releases into an equivalent toxicity concentration of 2,3,7,8-tetrachorodibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic member of this class of compounds. Using this WHO procedure, the annual releases of TEQDF-WHO98 to the U.S. environment over the three reference years are 14,000 g in 1987, 3,400 g in 1995, and 1,400 g in 2000.

This analysis indicates that between reference years 1987 and 2000, there was a significant reduction in the releases of dioxin-like compounds to the circulating environment of the United States from regulated industrial sources. In 1987 and 1995, the leading source of dioxin emissions to the U.S. environment was municipal waste combustion; however, because of reductions in dioxin emissions from municipal waste combustors, it dropped to the 4th ranked source in 2000. Burning of domestic refuse in backyard burn barrels remained fairly constant over the years, but in 2000, it emerged as the largest source of dioxin emissions to the U.S. environment that could be reliably quantified. Other potentially large sources were identified, but were not included in the inventory due to uncertainties in available data. These included forest fires and landfill fires.

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