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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