Open Letter to the Community from Dr. Michael Carson
#4: Understanding Dioxin Concentrations in Blood

Recent print and television coverage of the Michigan Department of Community Health's (MDCH) evaluation of dioxin blood levels in residents living along the Tittabawassee River, including individual results of the 25-person study, has brought in many inquiries to me and Dow Chemical. As a physician, I feel it important to let people know what the numbers mean.

The MDCH has not yet presented their full study report, so only a few individuals have reported their values. It is also important to note that their investigation is not designed to determine health effects. MDCH stated "Although exposure may be defined, exposure to a chemical does not mean an effect would be expected or would occur. The source of the exposure may not be defined."

The fact is that the individual dioxin blood levels reported are consistent with background levels in the general public, and the overall range is consistent with what other studies have found in the U.S. and Europe. In short, while some older individuals do have levels that are approaching the upper levels of background, this is not unexpected and is not a cause for alarm.

It is helpful to understand how dioxin gets into the blood. Approximately 95 percent or more of an individual's background dioxin exposure comes from our diet, according to the World Health Organization and the U.S. Environmental Protection Agency. Numerous scientific studies have measured the presence of dioxins in animal fat of foods, including beef, pork, fish, eggs, and dairy products, according to U.S. Food and Drug Administration and Department of Agriculture.

Studies have confirmed that older people are more likely to have higher blood dioxin levels simply because they were exposed and ingested more of it during their lives. Overall, human exposure to dioxin is decreasing, and variations in diet, age, sex, amount of body fat, and bodily elimination functions primarily determine the differences in background blood dioxin concentrations from person to person.

Locally, the data that has been recently reported is consistent with the range of background.

The U.S. Centers for Disease Control (CDC) has just released the most recent age-specific reference levels available to date in the U.S¹. A major study of 588 individuals tested between 1996 and 2001 showed that even for individuals with no unusual dioxin exposures, older individuals had a greater range of blood dioxin concentrations than younger ones. The chart below shows the CDC results:

Chart: Dioxin TEQ reference by age group based on studies from 2004 CDC study.

For Example: If you are 45 years old with a blood dioxin level of 32, you fall within the background range from the CDC study.

Clearly, dioxin blood concentrations vary significantly by age. If an individual's dioxin blood level falls within the range of the graph, it can be reasonably concluded that the blood dioxin concentrations reflects background levels. The graph represents where 95 percent of the study subjects fell for a specific age group, i.e., 95 out of 100 people studied fell within these ranges.

Even if an individual's dioxin blood level falls outside of the background range, this level could still be the result of background exposure. However, at that point it is prudent to examine occupational or environmental exposure. This will be an objective of a major study underway by the University of Michigan, which will evaluate local exposure for residents of the Tittabawassee River floodplain and Midland.

The background concentrations reported in the CDC study reflect subjects from North Carolina, Missouri, New York and Louisiana. A study of Michigan residents could be different, which is why the University of Michigan exposure study will provide useful information on background blood dioxin concentrations locally.

It is understandable that providing simple blood dioxin level concentration numbers to local residents, without information to explain what those numbers mean or how they compare to other populations, would cause heightened concern.

But the good news is that based on this very small sample of residents who have chosen to report their test results, local dioxin blood levels are consistent with typical background concentration and are quite comparable to levels found in other locations in the U.S. and Europe. This is not a cause for alarm.

Dr. Michael Carson
Regional Medical Director
The Dow Chemical Company

¹Patterson, DG, et. al., Age Specific Dioxin TEQ Reference Range, Organohalogen Compounds, Vol. 66, 2004:pp2878-2883.