Health Information Summary for CF Members
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IThe U.S. military used several different herbicide mixtures during the Vietnam War. These mixtures contained herbicides that were commercially available in the 1960's, but the mixtures themselves were made specifically for the U.S. military. In order to readily identify these different mixtures in the field, the storage drums for these mixtures used in Vietnam were painted with coloured bands, such as pink, purple, blue, white, green, and orange. The herbicide in the orange drums was an equal mixture of 2,4-D and 2,4,5-T (2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid). It became known as "Agent Orange", as this was the colour of the bands on the drums it was stored in. In Vietnam, more than 45 million liters of Agent Orange were sprayed (the most of any herbicide formulation) and less than 2 million liters of Agent Purple were sprayed during the war (Stellman et al., 2003).
Both Agent Orange and Agent Purple were 50-50 mixtures of 2,4-D and 2,4,5-T; the distinction is in the type of 2,4,5-T. Agent Orange was a 50-50 mixture of n-butyl ester 2,4-D and n-butyl ester 2,4,5-T. Agent Purple contained 50% n-butyl ester 2,4-D, 30% n-butyl ester 2,4,5-T, and 20% isobutyl ester 2,4,5-T.
TCDD is an abbreviation for 2,3,7,8-tetrachlorodibenzo- p -dioxin (which can also be abbreviated as 2,3,7,8-TCDD). TCDD was an unintended contaminant in the production of 2,4,5-T. Therefore, TCDD was also a component of herbicide mixtures containing 2,4,5-T, such as Agent Orange. According to the U.S. Institute of Medicine, " TCDD is thought to be the most toxic of the compounds " used in Vietnam (Institute of Medicine, 2005).
TCDD is one specific type of chemical from a family of chemicals known as "dioxins". Some of the chemicals within the dioxin family are considered to be toxic whereas others are much less toxic. TCDD is considered to be the most toxic of the dioxins. Because of this, the toxicity of mixtures of dioxins is usually described in relation to TCDD. The scientific term for this is "toxic equivalent", or TEQ: the toxicity of a mixture of dioxins, expressed as an amount of TEQ, is comparable to the toxicity of the same amount of pure TCDD.
In later parts of this document ( "Is Agent Orange the only source of TCDD?" and "Can TCDD be measured in our bodies" ), some of the cited references discuss amounts of TEQ and amounts of TCDD. For simplicity, only the term "TCDD" is used in those sections.
The term "part per million" is used to describe the concentration of one substance (the "part") contained within another substance (the "per million"). Using the example of 2 ppm TCDD contamination, every million parts of Agent Orange would contain 2 parts of TCDD. If the TCDD contamination were 2 ppm, then a 55-gallon drum of Agent Orange would contain 4 drops of TCDD. If the TCDD contamination were 47 ppm (such as an Agent Purple sample), a 55-gallon drum of Agent Purple would contain about one third of a one-ounce shot glass of TCDD.
A part per trillion is a very tiny amount. One ppt is equivalent to 1 second in about 32 000 years, 1 drop of water in 40 Olympic size swimming pools, or the distance of 1 centimeter (the width of your "pinkie" fingernail) in 1200 round trips between Fredericton and Vancouver.
It is not known with certainty how much TCDD was in the Agent Orange and Agent Purple used by the United States during the Vietnam War. Because TCDD was an unintended contaminant, it was not routinely measured at the time these herbicide mixtures were made. However, the TCDD content can be estimated from samples collected from these herbicides. A survey of 15 million pounds of Agent Orange (200 samples) conducted by the U.S. Air Force revealed that the average TCDD content of the mixture was 1.91 ppm (parts per million, equivalent to mg/kg), and 68% of the samples contained 0.5 ppm or less of TCDD (Kearney et al., 1973). Four saved samples of Agent Orange left over from testing at Eglin Air Force Base in Florida had a mean TCDD concentration of 2.4 ppm (range 0.04 to 6.4 ppm); an analysis of 490 Agent Orange samples from U.S. and Pacific inventories had an average concentration of 2 ppm (Young et al., 2004b). Recently, it has been suggested that these values are an underestimate, and that an average TCDD contamination of 13 ppm for Agent Orange may be more realistic (Stellman et al., 2003).
Less information is available for Agent Purple. In the testing of 200 Agent Orange samples mentioned above, the four highest TCDD values of 17, 22, 33, and 47 ppm were actually Agent Purple, and not Agent Orange (Stellman, 2003). One saved Agent Purple sample at Eglin Air Force Base contained 45 ppm TCDD (Young et al., 2004b).