used in Vietnam during the war include Agent Blue, Agent Purple, Agent Pink, and Agent Green. The names of the herbicides were derived from the color-coded bands around the 55-gal (208-L) drums used to ship and store them (Young, 2009). The military use of herbicides has been discussed in several other Institute of Medicine (IOM) reports (IOM, 1994, 2003, 2008) and two books (Buckingham, 1983; Young, 2009), and will not be described in detail here.

The tactical herbicides used in Vietnam were intended to kill a broad spectrum of plants. Agent Orange and Agent White were used against broadleaf plants and woody shrubs and trees, including mangroves. Agent Blue was effective against grasses and grains, such as rice (Young, 2009).

Herbicide Composition

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) was the main active ingredient of Agent Orange and the herbicides used earlier in the Vietnam War. As a result of the synthesis of 2,4,5-T, it was contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD, also referred to as TCDD). Production of 2,4,5-T ceased in 1979 when the US Environmental Protection Agency (EPA) canceled all registrations for its use (EPA, 1979). The EPA based that decision on its toxicity resulting from its unavoidable TCDD contamination. Of the herbicides used in Vietnam, only those containing 2,4,5-T were contaminated with TCDD. 2,4-dichlorophenoxyacetic acid (2,4-D)—a second active ingredient of Agent Orange, Agent White, and Agent Purple—was and continues to be a widely used herbicide around the world. Its human health and environmental risks were assessed by the EPA in 2005 to support its reregistration. It is permitted for agricultural and residential herbicide use (EPA, 2005).

The magnitude of TCDD contamination in the herbicides used in Vietnam is the subject of controversy. Part of the issue is that the herbicides were not tested for TCDD content when manufactured or used. Assessment of TCDD content is based on the analysis of the herbicide stockpiles that were stored at Johnston Island in the Pacific and the Naval Construction Battalion Center in Gulfport, Mississippi, before their destruction by at-sea incineration in 1977. The TCDD content was known to vary by herbicide and by production run. Some manufacturers were able to reduce the TCDD concentrations in their 2,4,5-T during the 1960s, particularly after 1967 when one manufacturer installed an

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