Rare Cases of High Levels of Dioxin Exposure

December 20, 2004; Updated November 14, 2005

Case Histories

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.

Health Effects

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 of dioxin.

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. (See man-made dioxin sources.) Dioxin is produced naturally in volcanoes and forest 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 backyard 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 be lower.

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.

Notes

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.