US EPA

Background

The purpose of The Inventory of Sources of Dioxin in the United States (2005 External Review Draft) is to present the most current inventory of sources and environmental releases of dioxin-like compounds in the United States. This is a comprehensive overview of what is known about sources that release dioxin into the air, land and water of the United States.

The inventory is a listing of sources by category combined with estimates of releases of dioxin to the environment from these sources. Estimates of environmental releases are associated with three calendar years: 1987, 1995 and 2000. This provides a point of reference for observing any changes in the amount of dioxin that is released to the environment with the passage of time. Between 1987 and 2000 there have been significant changes in industrial processes; combustion technologies have been improved; and national regulations are in place that may have reduced the amount of dioxin that is released from sources. The Inventory is intended to capture and document these changes in a rigorous and transparent manner.

The term dioxin-like includes:

• chemical compounds of polychlorinated dibenzo-p-dioxins (CDDs),
• polychlorinated dibenzofurans (CDFs) having chlorine atoms in the 2,3,7,8 positions on the molecule,
• and certain specific polychlorinated biphenyls (PCBs).

Dioxin-like refers to the fact that these compounds have similar chemical structure and physical-chemical properties and invoke a common battery of toxic responses. For simplicity, this group of compounds is often referred to as dioxin. When released into the environment from sources, these chemicals persist and bioaccumulate in fatty tissues of animals and humans. Consequently, the principal route of chronic population exposure is through the dietary consumption of animal fats, fish, shellfish, and dairy products. Dioxin-like compounds are persistent in soils and sediments, with environmental half-lives ranging from years to several decades.

The 1998 draft inventory presented annual estimates of environmental releases for reference years 1987 and 1995. A meeting of scientific and engineering experts was convened June 3-4, 1998, to review the scientific soundness of EPA's dioxin inventory. Overall, the reviewers found, in their peer review report to EPA, the inventory report to be comprehensive and well documented and the emission factor approach that was used to develop the inventory to be scientifically defensible.

The current inventory reflects comments made by the review committee and also represents an update with the inclusion of a third reference year, 2000. In addition, this draft document concludes that, between 1987 and 2000, there was an approximately 89% reduction in the release of dioxin-like compounds to the circulating environment of the United States from all known sources combined. Annual emission estimates of releases of CDDs/CDFs to air, water, and land from reasonably quantifiable sources are approximately 1,529 grams (3.37 pounds) in reference year 2000; 3,280 grams (7.23 pounds) in reference year 1995; and 13,962 grams (30.78 pounds) in reference year 1987.

In 1987 and 1995, the leading sources of dioxin emissions to the U.S. environment were municipal waste combustors. The inventory also identifies bleached chlorine pulp and paper mills as a significant source of dioxin to the aquatic environment in 1987 but a minor source in 1995 and 2000. The inventory concludes that the major source of dioxin in 2000 was the uncontrolled burning of refuse in backyard burn barrels in rural areas of the United States.

The reduction in environmental releases of dioxin-like compounds from 1987 to 2000 is attributable to:

• source-specific regulations,
• improvements in source technology,
• advancements in the pollution control technologies specific to controlling dioxin discharges and releases,
• and the voluntary actions of U.S. industries to reduce or prevent dioxin releases.

History/Chronology

The following is a brief history of the development of the dioxin inventory.

• 1995 - EPA's Science Advisory Board (SAB) reviewed EPA's Dioxin Reassessment. The SAB recommended that EPA undertake a detailed assessment of sources of dioxin.
• 1998 - In response to the recommendation of the SAB, EPA released the first external review draft report entitled, The Inventory of Sources of Dioxin in the United States (EPA/600/P-98/002Aa).
• 1998 - Independent peer review panel gives support to the technical approach and scientific basis of the dioxin inventory (see their peer review report). This review recommended that EPA update the inventory in order to capture changes in dioxin releases resulting from changes in technologies and regulatory requirements.
• 1999 - EPA began the development of the year 2000 update to the dioxin inventory.
• 2001 - EPA releases an electronic Database of Sources of Environmental Releases of Dioxin-Like Compounds in the United States containing dioxin emission factors specific for releases from sources in reference years 1987 and 1995.
• 2005 - EPA releases for public comment and peer review the external review draft of the dioxin updated inventory.

Next Steps

On September 13 -15, 2005, EPA will host a meeting in Washington, DC for the purpose of providing an independent scientific peer review of this document.[ Aug 12 Federal Register Notice] Following the completing of the scientific peer review, EPA will review all comments received, including public comments, to determine further work that needs to be accomplished prior to completing the document.

A final report will be published on the NCEA Web site that addresses both public and peer review comments.

U.S. EPA. The Inventory of Sources of Dioxin in the United States (External Review Draft 2005). U.S. Environmental Protection Agency, Washington, D.C., EPA/600/p-03/002a, 2005.