Chemical Description and Toxicology
Chemically, Agent Orange is an approximately 1:1 mixture of two phenoxyl herbicides – 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) – in iso-octyl ester form.
Numerous studies have examined health effects linked to Agent Orange, its component compounds, and its manufacturing byproducts.
Prior to the controversy surrounding Agent Orange, there was already a large body of scientific evidence linking 2,4,5-T to serious negative health effects and ecological damage. But in 1969, it was revealed to the public that the 2,4,5-T was contaminated with a dioxin, 2,3,7,8-tetrachlorodibenzodioxin (TCDD), and that the TCDD was causing many of the previously unexplained adverse health effects which were correlated with Agent Orange exposure. TCDD has been described as "perhaps the most toxic molecule ever synthesized by man". Internal memoranda revealed that Monsanto (a manufacturer of 2,4,5-T) had informed the U.S. government in 1952 that its 2,4,5-T was contaminated. In the manufacture of 2,4,5-T, accidental overheating of the reaction mixture easily causes the product to condense into the toxic self-condensation product TCDD. At the time, precautions were not taken against this unintended side reaction, which caused also the Seveso disaster in Italy in 1976.
In 1979, the Yale biologist Arthur Galston, who specialized in herbicide research, published a review of what was known at the time about the toxicity of TCDD. Even "vanishingly small" quantities of dioxin in the diet caused adverse health effects when tested on animals. Since then, TCDD has been comprehensively studied. It has been associated with increased neoplasms in every animal bioassay reported in the scientific literature. The National Toxicology Program has classified TCDD as "known to be a human carcinogen", frequently associated with soft-tissue sarcoma, non-Hodgkin's lymphoma, Hodgkin's lymphoma and chronic lymphocytic leukemia (CLL).
While the two herbicides that make up Agent Orange, 2,4-D and 2,4,5-T, remain toxic over a short period—a scale of days or weeks—they quickly degrade. A 1969 report authored by K. Diane Courtney and others found 2,4,5-T could cause birth defects and stillbirths in mice. Several studies have shown an increased rate of cancer mortality for workers exposed to 2,4,5-T. In one such study, from Hamburg, Germany, the risk of cancer mortality increased by 170% after working for 10 years at the 2,4,5-T-producing section of a Hamburg manufacturing plant. Three studies have suggested prior exposure to Agent Orange poses an increased risk of acute myelogenous leukemia in the children of Vietnam veterans.
Starting in 1991, the US Congress asked the Institute of Medicine to review the scientific literature on Agent Orange and the other herbicides used in Vietnam, including their active ingredients and the dioxin contaminant. The IOM found an association between dioxin exposure and diabetes.
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