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Researching SourcetoExposure Pathways for DioxinLike Compounds Under the Dioxin Exposure Initiative

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Title: Researching SourcetoExposure Pathways for DioxinLike Compounds Under the Dioxin Exposure Initiative


1
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
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 EPAs 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 EPAs 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. .
Impact and Outcomes
Dioxin Sources Direct
measurement of dioxin source emissions, directed
by ORDs 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.
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 Nations Environmental Program
that is used to develop national sources
inventories. This toolkit directly mimics EPAs
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 ORDs 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 ORDs 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 ORDs
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.
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
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.
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.
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. .
EXPOSURE MODELING STUDIES Simple
pharmacokinetic models have been used to
translate dioxin intakes to body burdens. One
study looked at exposures throughout the 20th
century, and into the 21st century, and showed
how general population body burdens rose
throughout the 20th 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.
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.
References
A listing of 50 publications associated with
Dioxin Exposure Initiative is available under
separate cover
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