2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) and Agent Orange

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) is a broad leaf plant defoliant developed in the 1940s and widely used in agriculture through the early 1980s when the Environmental Protection Agency (EPA) ended its use on food crops in the United States. Agent Orange is a defoliant that is a mixture of 2,4,5-T and 2,4-D that was used during the Vietnam War. Agent Orange has subsequently been suspected of causing serious illness including cancer in Vietnam veterans that were exposed to the herbicide during the war.
Both 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-T are synthetic auxins. Auxins occur naturally as plant growth substances (growth hormones) that regulate plant growth behavior. Both of these chemicals are members of the phenoxy family of herbicides. The half-life of 2,4-D is estimated to be 7-10 days and soil microbes are primarily responsible for its degradation. Although microbes also break down these chemicals in aquatic systems tests have shown trace amounts in surface and groundwater across the United States and Canada.

For more details about the manufacture, chemistry, and toxicity of the phenoxy family of herbicides, see http://en.wikipedia.org/wiki/2,4-D