# Presentation: 467591

## Researching Source-to-Exposure Pathways for Dioxin-Like Compounds Under the Dioxin Exposure Initiative

- Matthew Lorber1, David Cleverly1, John Schaum1, Brian Gullet2, Paul Lemieux2, Dwain Winters3, Joseph Ferrario3, Christian Byrne3,
- George Fries4, Cindy Deyrup4, Randall Lovell5
- 1National Center for Environmental Assessment, 2National Risk Management Research Laboratory, Office of Research and Development
- 3Office of Pesticides, Prevention, and Toxic Substances, 4United States Department of Agriculture,  5Food and Drug Administration

- Can we quantify the pathways of dioxin exposure, starting from sources of dioxin release, through the environment and into the food chain, in order to assist in the development of a regulatory strategy for this important class of compounds?

**Research Goals**

**Impact and Outcomes**

**Science Question**

- The research program has reduced uncertainty in risk assessment by:
-   Providing data, tools and expertise that are being used worldwide.  Dr. Heidelore Feidler, an internationally recognized dioxin sources expert, has developed a “Toolkit” for the United Nation’s Environmental Program that is used to develop national sources inventories.  This toolkit directly mimics EPA’s Sources Inventory structure and approach;
-   Identifying ball clay as a feed contaminant (the first reported incident) has lead to similar worldwide findings of feed contaminated with dioxin-like compounds (PCBs in Belgium poultry/pork feed; contaminated citrus pulp in Brazil; contaminated European poultry feeds, etc.);
-   Developing laboratory procedures for measuring dioxins at trace levels in environmental matrices, through the DEI, established EPA as worldwide leaders in dioxin chemistry;
-   Employing ORD’s procedures to evaluate exposures in site-specific assessments as well as national regulations.  Exposure and risk assessments involving incinerators, such as the East Liverpool, Ohio hazardous waste incinerator or the Columbus Municipal Solid Waste Incinerator, have all used ORD’s modeling and exposure pathway procedures.  Risk assessments associated with national regulations on land application of sewage sludge, pentachlorophenol, 2,4-D, and others, have similarly relied on ORD’s exposure procedures;
- With these lines of research into source characterization, air-to-plant-to-animal modeling, food and feed studies, pharmacokinetics, and the like, ORD will provide the Agency with a scientific basis upon which it could develop a regulatory strategy that could reduce exposures of Americans to this important class of compounds.

**References**

- A listing of 50 publications associated with Dioxin Exposure Initiative is available under separate cover

***                    ******Dioxin Sources***
*Direct measurement of dioxin source emissions, directed by*
*ORD’s National Risk Management Research Laboratory,  *
*includes such diverse point sources as diesel engine tail *
*pipes, incinerator stacks, and controlled laboratory *
*bench-scale mockups of incinerators.  Also, studies *
*have sought to quantify diffuse sources of release, *
*such as from backyard barrel burning and forest fires. *
*The National Center for Environmental Assessment *
*has developed the Dioxin Sources Inventory, which*
*attempts to quantify all known sources of dioxin-like*
*Compounds.  The graph to the right shows the*
*Inventory for years 1987 and 1995.** An inventory for a *
*third reference year, 2000, is currently under review.  *

*   **Environmental Fate and Transport *
*The National Dioxin Air Monitoring Network includes 34 ambient monitoring stations in rural and background settings of the United States. The purpose of the network is to obtain national baseline/background air measurements of dioxins over a period of time, and secondarily, to develop data that possibly can be used in future national-scale air modeling exercises. The link between sources and animal exposures has also included model simulation work. Models of the air-to-plant pathway have demonstrated that deposition of atmospheric dioxins, and particularly dioxins in the gas phase, is the primary pathway that leads  to terrestrial vegetation contamination, and hence terrestrial animal exposures. *

- 	In September of 1994, the National Center for Environmental Assessment released its public review draft of the Dioxin Reassessment.  At that time, they also announced the start of the Dioxin Exposure Initiative, DEI,  to fill critical data gaps regarding the sources of dioxin that contribute to human exposure.  The DEI was identified as a multi-year effort that would extend beyond the current Reassessment effort.  However, particular emphasis would be placed on gaining as much information as possible that could be incorporated into the final Reassessment.
- 	The fundamental goal of the Initiative is to _quantitatively link dioxin sources to general population exposure_.  This is being accomplished by pursuing two simultaneous lines of inquiry. One approach is to focus on identifying  sources of dioxin-like compounds and work forward along their pathways of transport and deposition. The second is to start with human body burdens and work backwards through the process of bioaccumulation and uptake.   As these two lines of inquiry merge, they should provide an adequate understanding to enable EPA to target future exposure reductions to those sources and pathways that most significantly contribute to human risk.   An additional goal of the initiative is to estimate, where possible, past trends in dioxin exposure and to establish a current baseline for monitoring future trends.

*                     **Analytical Chemistry*
*The Office of Pesticides, Prevention, and Toxic Substances Laboratory at the Stennis Space Center in Bay St. Louis, Misssissippi, has established itself as a world-wide leader in dioxin chemistry.   That laboratory pioneeered the methods for trace chemical analysis of dioxin-like compounds in a variety of matrices, such as air, soil, blood, and importantly, food.  They have conducted the analysis of virtually all of the samples that have been taken in studies of the Dioxin Exposure Initiative.  *

***EXPOSURE  MODELING STUDIES***
*	**Simple pharmacokinetic models have been*
* **used to translate dioxin intakes to body burdens.  *
*One study looked at exposures throughout the 20**th** *
*century, and into the 21**st** century, and showed *
*how general population body burdens rose throughout the 20**th** century, but are currently and will continue to decline within the population.  A second study looked*
* **at the impact of breast feeding on the body burdens of dioxins in infants. The graph to the left shows how the infant body burden varies according to the amount of breast-feeding, from no breast-feeding, to regimes of 6 weeks, 6 months, 1 year, and 2 years.  *

***Food and Feed***
*	**A major finding of the Dioxin Reassessment is that consumption of animal food products, particularly terrestrial food animal products, dominates human exposures:  over 95% of typical background exposures can be attributed to dioxins present in the fat of consumed animal food products. Efforts to more directly quantify human exposure through food consumption began with EPA’s cooperative efforts with the USDA in the mid-1990s to sample beef, pork, and poultry from slaughterhouses.  National studies of dioxin in milk were also conducted using EPA’s radiation network, ERAMS.  Results from these critical studies were used to estimate background exposure of dioxin-like compounds.  The table to the right is a principal result of the Dioxin Reassessment, and it was made possible by the food studies of the Dioxin Exposure Initiative.*
*	**.  *

* **A finding of a small number of highly contaminated poultry samples was traced back to the poultry feed, which was contaminated by a minor component, ball clay, added  as a flowability agent.  This was the beginning of a primary focus in the DEI, which was on the role of animal feeds in the  contamination of the food supply.  Animal feed studies have included a study to sample minor feed components like ball clay, and a second study to sample major and minor components of dairy feeds nationally.*
*	**.  *