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US EPA Reassessment

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The EPA's third and most recent reassessment study took almost four years and cost $4 million. Because of the way that dioxin was thought to mimic hormones in binding to receptors in the cells, the EPA considered a range of chemicals that act in this way including the family of dioxins, dibenzofurans (or furans) and PCBs calling them 'dioxin-like' chemicals.

The study involved about 100 scientists including non-EPA scientists used to peer review each chapter as it developed. EPA management decided that:

since the question of dioxin's risk had been marked by considerable controversy for more than a decade, we should pursue a process that would achieve scientific consensus on this issue... As a first step, it would be conducted as a cooperative effort, written by both EPA scientists and external scientists and peer-reviewed by scientists outside the Agency who were experts on dioxin. We hoped this would help ensure not only that the most current, most scientifically accepted information was used, but also that all scientific views would be heard and debated.

Public comments were invited, three peer-review workshops were held and the drafts of each chapter, most of which were authored or co-authored by outside scientists, were reviewed and revised by a panel of scientists from other government agencies.

In 1994 a draft report was released and open to public comment and in 1995 the final report was published. The report stated that:

There is adequate evidence from studies in human populations as well as in laboratory animals and from ancillary experimental data to support the inference that humans are likely to respond with a plethora of effects from exposure to dioxin and related compounds.

Most significant in this analysis is the heightened concern about noncancer effects in humans, including disruption of the endocrine, reproductive, and immune systems, as well as dioxin's impact on the developing fetus, which may occur in some cases at or near background levels.

The report referred to studies that had found "decreased sperm count in men, higher probability of endometriosis in women, weakened immune systems, and other health problems" as a result of dioxin exposure in the general population at levels already found in the food supply. The report claimed that current background levels of dioxins could be posing a risk of one additional death in every thousand or one in every ten thousand, even though as little as 30 pounds of dioxin may be released in the US each year.

The EPA study also examined the sources of dioxin in the environment and the ways in which people are exposed. It concluded: "The presence of dioxin-like compounds in the environment has occurred primarily as a result of anthropogenic practices", that is human activities. It based this conclusion on the sampling of tissue of ancient humans and sediments in lakes near industrial centres in the US which showed low levels of dioxins prior to 1920.

The study found that most dioxin is carried through the air and taken up by plants, which are in turn eaten by fish and animals which bioaccumulate the dioxin in their fatty tissues. By the time humans eat the fish, beef, dairy products etc, the dioxin is far more concentrated than it originally had been in the environment and it accumulates in the fatty tissues of humans. Ingestion of dioxin via food is a far more significant means of exposure than breathing in polluted air. The report noted that the major source of dioxin was incinerators, and that sources such as chemical manufacturing could be significant but that there was insufficient data on them to be able to say.

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Additional Material

US EPA Reassessment Reports

US EPA, 1995, Estimating Exposure to Dioxin-Like Compounds.

US EPA, 1995, Health Assessment for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin and Related Compounds.

Montague, Peter, 1994, Dioxin Reassessed - Part 1, Rachel's Hazardous Waste News, No. 390.


© 2003 Sharon Beder