Friday, June 3, 2016

‘Doomsday Chemical’ Update: Whatever Happened to Dioxin?

Dioxin, once proclaimed by the environmental community as the “doomsday chemical” of the 20th century and the “deadliest substance ever created by chemists,” has faded from the media spotlight. Why?
Why did the EPA official who recommended the evacuation of Times Beach, Missouri, admit that he made a mistake and that the evacuation of this community following the spraying of dioxin-contaminated oil on roads, and a subsequent flood, was an unnecessary overreaction brought about by the beliefs of Dr. Vernon N. Houk, Director of The Center for Environmental Health at Centers for Disease Control and Prevention?
What are the latest facts regarding adverse human health effects from exposure to dioxin?
Although dioxin’s teratogenic (birth) defects in some animals were not discovered until 1970 by Dow Chemical Company scientists, the industrial community was aware of a mysterious skin disease “chloracne” since it was first reported by Herxheimer in Germany in 1899. Choracne was originally incorrectly attributed to chlorine gas exposure and only in 1957 was it recognized by the German scientists Kimmig and Schultz that dioxin impurities in certain chlorinated phenols were responsible.
Unfortunately, this research paper was not widely read by the scientific community and it was not until 1969 that the existence of dioxins and their acnegenic properties were widely publicized. We now know that dioxin (really a family of related chlorinated chemicals, the most toxic of which is 2,3,7,8-tetrachlorodibeno-p-dioxin or TCDD) is produced when chlorinated phenols, used to manufacture herbicides (such as 2,4-D), insecticides, and antiseptics (hexachlorophene) are heated to a high temperature. In particular, during the manufacture of the herbicide 2,4,5-T, which, in combination with 2,4-D, comprised Agent Orange, it was necessary to heat the chemical ingredients in a large “pressure-cooker” chemical reactor.
As was later discovered, if the temperature of this process is not very carefully controlled, then variable amounts of the byproduct dioxin can form.  Some chemical companies were better able to control this temperature than others. In fact, of the seven companies involved in the production of 2,4,5-T for use in Agent Orange, one company consistently produced batches relatively high (>500 parts per billion) in dioxin. Although the Dow Chemical Company, the largest producer of 2,4,5-T, was eventually able to produce very “clean” — essentially dioxin-free — 2,4,5-T, public pressure forced the discontinuance of the manufacture of this chemical, despite the fact that pure 2,4,5-T has always been a perfectly safe herbicide, like the still-used 2,4-D.

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