Rare Cases of High Levels of Dioxin Exposure
December 20, 2004; Updated November 14, 2005
The dioxin poisoning of Ukrainian presidential
candidate, Viktor Yushchenko, raises questions about dioxin
blood levels in humans and how such levels should be interpreted.
The Associated Press reported December 17, 2004 that
Yushchenko has a blood level of dioxin of 100,000 units (parts
per trillion), the second highest level ever recorded in a
human. Tests done by Abraham Brouwer, professor of environmental
toxicology at the Free University in Amsterdam, show the particular
type of dioxin found in the candidate's blood was pure 2,3,7,8-TCDD,
the most potent of all the dioxin-family compounds1.
Cases of dioxin poisoning are rare. In 1998,
two Austrian women unknowingly ingested high levels of 2,3,7,8-TCDD.
One of those two women had the highest blood level of 2,3,7,8-TCDD
ever recorded in a human victim of dioxin poisoning. In 1976,
an industrial accident in Seveso, Italy exposed a large population
to high levels of a mixture of dioxin family compounds.
The chart above indicates the relative magnitudes
of such rare exposures2. In comparison to the high
exposures shown, levels of 2,3,7,8-TCDD in the average U.S.
resident are quite low--below the level of detection of 5.2
ppt, according to the U.S. Centers for Disease Control and
Prevention's Third National Report on Human Exposure to Environmental
Chemicals (July, 2005). Current, undetected levels represent
a decline from an estimated blood level of 20 ppt in 19703.
Yushchenko has developed chloracne, a serious
skin condition symptomatic of high exposure to dioxin. The
two Austrian women and some of the Seveso population developed
the same condition. Gastrointestinal symptoms were also reported
in these cases. Other health effects of such high exposures
to dioxin, if present, are not as clearly manifested.
Background on Dioxin
Dioxin normally occurs as a complex mixture
of a family of compounds which vary greatly in toxicity.
Sometimes the term dioxin is used to refer only to 2,3,7,8-tetrachlorodibenzo-p-dioxin
(2,3,7,8-TCDD), the most well-studied and the most toxic form
Where does dioxin come from? No one makes dioxin
on purpose except for research purposes; it is a trace byproduct
of many industrial processes, especially those involving combustion.
dioxin sources.) Dioxin is produced naturally in volcanoes
fires and burning vegetation, such as wood, in domestic
stoves and fireplaces. This substance is a ubiquitous trace
byproduct of the combustion
of organic compounds and small amounts of chloride.
Dioxin emissions to the environment from man-made
sources are estimated to have declined
92 percent since 1987, thanks to a combination of government
regulation and voluntary industry initiative. As dioxin emissions
from industry decline, largely unregulated sources, such as
burning of trash and residential wood burning, rise in
significance as contributors to dioxin emissions.
How does dioxin get into the human body? According
to the Interagency
Working Group on Dioxin (2004), more than 95% of human
exposure to dioxin is through the diet. How does dioxin get
into our food? Air emissions of pollutants, including dioxin,
settle on vegetation that is fed to livestock. Dioxin then
accumulates in animal fatty tissue and is conveyed to humans
through meat and dairy products. Fish and other aquatic organisms
ingest dioxin that is washed into surface water bodies from
land, providing another potential pathway into the food chain.
Dioxin taken in through the human diet dissolves in the fatty
components of blood, eventually accumulating in fatty tissue.
The human body eliminates dioxin slowly; at any given time,
the dioxin concentration in the fatty tissue of a human body
is a function of the competing rates of accumulation and elimination.
Trends in Body Levels of Dioxins
The graphics below illustrate trends in human
body levels of dioxins over the past several decades. The
term "dioxins" here is defined as 17 polychlorinated dibenzo-p-dioxin
and polychlorinated dibenzofuran compounds, including the
most potent and widely studied of this family, 2,3,7,8-TCDD.
Levels are indicated by "TEQ," or "toxic equivalents," a quantitative
measure of the combined toxicity of a mixture of dioxin chemicals.
The figure above illustrates that dioxin levels
in human blood are declining in people of all birth years,
but the youngest of the population begin life with much lower
levels of dioxin than their parents or grandparents, and will
never experience the high body levels accumulated by persons
alive during the middle decades of the 1900s.
Consistent with declining dioxin levels in blood,
average dietary intakes of dioxins have declined dramatically
over the past 20 years in the U.S. and Western Europe: Dioxin
body levels in people, 15-35 years of age have decreased substantially
over time. The year 2000 data includes PCBs as well as dioxins.
Without PCBs, this data point would be even lower, and considering
only 2,3,7,8-TCDD levels, all data points on the graph would
Dioxin body levels in people, 15-35 years of
age have decreased substantially over time. The year 2000
data includes PCBs as well as dioxins. Without PCBs, this
data point would be even lower, and considering only 2,3,7,8-TCDD
levels, all data points on the graph would be lower.
1Pure 2,3,7,8-TCDD is generally unavailable except
for research purposes through scientific laboratory suppliers.
2 All levels shown in the graphic represent exposures
to 2,3,7,8-TCDD, except for the two Seveso data points, which
represent exposures to a mixture of dioxin compounds.
3 Aylward, L., Hayes, S. (2002). Temporal trends
in human TCDD body burden: Decreases over three decades and
implications for exposure levels. Journal of Exposure Analysis
and Environmental Epidemiology 12, 319-328.