Dioxin continues to be the focus of research internationally. More than 2,000 scientific articles and studies have been published on dioxins and furans since the U.S. Environmental Protection Agency (EPA) released its year 2000 “Draft Dioxin Reassessment.”
The Weight of Evidence
The scientific and health data have only consistently demonstrated that relatively high exposures to dioxin may cause chloracne. While health effects have been reported in some epidemiology studies, there have been no consistent findings of disease risk across studies. Although some people in rare situations (including highly exposed workers and communities like Seveso, Italy that experienced industrial accidents) have been exposed to very high levels of dioxin (i.e. hundreds to thousands of times higher than typically found in the environment), no consistent findings of health effects are evident across the many studies of human health, including Dow’s studies on its own exposed employees. Temporary liver and other biochemical changes have been reported in some human studies, but not consistently. These temporary changes have not led to long-term adverse health impacts in people. For additional information, see “Health Studies” on the Other Opinions and Sources of Information page on this web site.
Dow Employee Studies
Since 1967, Dow scientists have conducted numerous studies among employees worldwide who, as a result of their work, have been exposed to a variety of chemicals, including dioxin. More than 200 studies have been published in peer-reviewed scientific journals. We know of no other company that has done more comprehensive employee studies over a longer time, or published more occupational health papers on its employees.
The largest single-plant study of workers who were exposed to dioxin during manufacturing operations from the late 1930s to 1979 at the Dow site in Midland, Michigan involves the health of 2,192 employees in the U.S. Some of these chlorophenol workers may have had dioxin levels in the past that were 10,000 times greater than background levels today. After an outbreak of chloracne, the health of these employees has been followed for more than 60 years — longer than any other dioxin-exposed employee population in the world. Researchers evaluated mortality rates for several diseases including cancer and those affecting the heart and lungs. Results show no indication of increased trends of disease related to dioxin exposure, with the exception of chloracne. Of those employees, 12 percent exhibited chloracne, and this group in particular showed overall cancer rates 50 percent lower than expected for the general population. Among all dioxin-exposed employees in the study, numbers of deaths from cancers of the stomach and prostate were slightly elevated, but numbers of deaths from other cancers were below expected. In any study, some causes of death will be higher and some will be lower based on normal variability. The results show no relationship between elevated dioxin exposure levels and cancer. The studies also show that Dow employees with dioxin exposure are healthy relative to the general population.
Since the initial study, which was published in a peer-reviewed occupational medicine journal in 1980, Dow has published 32 more studies on potential human health effects of dioxin exposure. These studies included evaluations of reproductive outcomes such as miscarriages and birth defects; diabetes; and effects on other organs like the liver and kidneys. Dow also evaluated levels of dioxin in the blood in a subset of the study group and the report was published in 2005. This study validated previous estimates of exposure based on jobs held, and the number of years they held them. Results of all studies demonstrate the same conclusion — that Dow employees who were exposed to high levels of dioxin in an industry setting generally do not have a higher risk of disease, with the exception of chloracne, which occurred in employees who experienced very high exposure levels and that effect is only temporary.
Currently, Dow supports additional studies that will improve our understanding of dioxin-related issues. For example, in Mid-Michigan Dow has commissioned a broad array of human health exposure and environmental studies to evaluate the potential impact of environmental dioxin. Specifically, the University of Michigan in 2006 reported the results of a two-year study of dioxin and furan and PCB exposure in the Midland, Michigan area and along the Tittabawassee River downstream from Dow manufacturing operations. Dow provided an unrestricted grant to the University of Michigan to conduct the study. To review the findings, please go to http://www.sph.umich.edu/dioxin/. While the results of this study are still being analyzed and reported, the initial findings from this study show little relationship between soil levels and levels in people living along the Tittabawassee River and in Midland. This finding should be reassuring and demonstrates that contact with contaminated soil does not contribute significantly to dioxin concentrations in humans. “The most important factor related to levels of dioxins in people’s blood is age,” (according to the University of Michigan study) and other factors such as amount of body fat and diet.
