2,4,5-Trichlorophenoxyacetic acid
Encyclopedia
2,4,5-Trichlorophenoxyacetic acid (2,4,5-T), a synthetic auxin
, is a chlorophenoxy acetic acid herbicide
used to defoliate
broad-leafed plants. It was developed in the late 1940s and was widely used in the agricultural industry until being phased out, starting in the late 1970s due to toxicity concerns. Agent Orange
, a defoliant used by the U.S. in the Vietnam War, was equal parts 2,4,5-T and 2,4-D.
2,4,5-T itself is of only moderate toxicity, with oral of 389 mg/kg in mice and 500 mg/kg in rats. However, the manufacturing process for 2,4,5-T contaminates this chemical with trace amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD is extremely toxic to humans. With proper temperature control during production of 2,4,5-T, TCDD levels can be held to about .005 ppm. Before the TCDD risk was well-understood, early production facilities lacked proper temperature controls and individual batches tested later were found to have as much as 60 ppm of TCDD.
In 1970, the United States Department of Agriculture halted the use of 2,4,5-T on all food crops except rice, and in 1985, the EPA terminated all remaining uses in the US of this herbicide. The international trade of 2,4,5-T is restricted by the Rotterdam Convention
. 2,4,5-T has since largely been replaced by dicamba
and triclopyr
.
Apart from agricultural uses, 2,4,5-T was also a major ingredient in Agent Orange
, a herbicide blend used by the U.S. military in Vietnam between January 1965 and April 1970 as a defoliant. Because of TCDD contamination in the 2,4,5-T component, it has been blamed for serious illnesses in many veterans who were exposed to it. Agent Orange often had much higher levels of TCDD than 2,4,5-T used in the US.
Auxin
Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development. Auxins and their role in plant growth were first described by...
, is a chlorophenoxy acetic acid herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
used to defoliate
Defoliant
A defoliant is any chemical sprayed or dusted on plants to cause its leaves to fall off. A classic example of a highly toxic defoliant is Agent Orange, which the United States armed forces used abundantly to defoliate regions of Vietnam during the Vietnam War from 1961 to 1970.Defoliants differ...
broad-leafed plants. It was developed in the late 1940s and was widely used in the agricultural industry until being phased out, starting in the late 1970s due to toxicity concerns. Agent Orange
Agent Orange
Agent Orange is the code name for one of the herbicides and defoliants used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. Vietnam estimates 400,000 people were killed or maimed, and 500,000 children born with birth...
, a defoliant used by the U.S. in the Vietnam War, was equal parts 2,4,5-T and 2,4-D.
2,4,5-T itself is of only moderate toxicity, with oral of 389 mg/kg in mice and 500 mg/kg in rats. However, the manufacturing process for 2,4,5-T contaminates this chemical with trace amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD is extremely toxic to humans. With proper temperature control during production of 2,4,5-T, TCDD levels can be held to about .005 ppm. Before the TCDD risk was well-understood, early production facilities lacked proper temperature controls and individual batches tested later were found to have as much as 60 ppm of TCDD.
In 1970, the United States Department of Agriculture halted the use of 2,4,5-T on all food crops except rice, and in 1985, the EPA terminated all remaining uses in the US of this herbicide. The international trade of 2,4,5-T is restricted by the Rotterdam Convention
Rotterdam Convention
The Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade, more commonly known simply as the ', is a multilateral treaty to promote shared responsibilities in relation to importation of hazardous chemicals...
. 2,4,5-T has since largely been replaced by dicamba
Dicamba
Dicamba is an herbicide. Brand names for formulations of this herbicide include Banvel, Oracle and Vanquish...
and triclopyr
Triclopyr
Triclopyr is a systemic, foliar herbicide in the pyridine group. It is used to control broadleaf weeds while leaving grasses and conifers unaffected....
.
Apart from agricultural uses, 2,4,5-T was also a major ingredient in Agent Orange
Agent Orange
Agent Orange is the code name for one of the herbicides and defoliants used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. Vietnam estimates 400,000 people were killed or maimed, and 500,000 children born with birth...
, a herbicide blend used by the U.S. military in Vietnam between January 1965 and April 1970 as a defoliant. Because of TCDD contamination in the 2,4,5-T component, it has been blamed for serious illnesses in many veterans who were exposed to it. Agent Orange often had much higher levels of TCDD than 2,4,5-T used in the US.