Dioxin, contaminants from agent orange

Schecter, A., Dai, L.C., Papke, O., Prange, J., Constable, J.D., Matsuda, M., Thao, V.D., Piskac, A.L., 2001. Recent dioxin contamination from Agent Orange in residents from a southern Vietnam city. J. Occup. Environ. Med. 43, 435 143. 

Schecter, A., Pavnuk, M., Malisch, R., Ryan, J.J., 2003. Are Vietnamese food exports contaminated with dioxin from Agent Orange J. Toxicol. Environ. Health 66, 1391-1404. 

Attention In dioxin was propelled into scientific and public scruliny as the result of the use uf the herbicide 2.3.5-T l Agent Orange) during the Vietnam conflict. Also, a major localized contamination resulted from an accident in a chemical plant in Seveso, Italy, in 1976... 

Mixtures with other herbicides also are used for weed control. The product Agent Orange, used extensively throughout Vietnam, was about 50% 2,4-D. However, the controversy about the use of Agent Orange was associated with a contaminant (dioxin) in 2,4,5-trichlorophenoxy acetic acid (2,4,5-T) (C8H5Cl303), not with 2,4-D. It should be well understood that 2,4,5-T is different from 2,4-D but similar to 2,4-D as a herbicide component of the defoliant.39... 

A combination of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-T (Agent Orange), was used by the US military during the Vietnam War for defoliation. Long-term health consequences from exposure to Agent Orange, in particular to dioxin contaminants, have been suspected. 

During the last decade, various remedial actions were carried out on dioxin-contaminated wastes in the United States and Europe. Historically, building rubble from industrial accidents was used as fill or disposed in the ocean. In 1977, about 2.2 million gallons of Agent Orange and similar herbicide formulations was incinerated on the ship Vulcanus in the Pacific (1). This solution was simplified by the ability to transfer the waste to the ship at a remote location in the Pacific and by the large quantity of liquid waste, which made the incineration on ship economically possible. The destruction efficiency of this at-sea-incineration was about 99.9% according to the limits of analytical detection at that time. 

Elevated human tissue dioxin levels found in certain areas after environmental contamination were described in previous publications (1-3). The highest levels were noted in human breast milk lipid a few years following heavy 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) contamination from herbicides, especially Agent Orange, sprayed in Vietnam. Elevated levels in this tissue from individuals living in the south of Vietnam decreased with time but were still above levels observed in samples from the North American continent ( ) It was hypothesized that the relatively low human tissue levels of dioxins observed in individuals living in the north of Vietnam may be attributed... 

Most of what is known about the toxicity of dioxins in the human comes from individuals exposed incidentally or chronically to higher levels (e.g., industrial accidents or presence in areas sprayed with Agent Orange or other herbicides contaminated with dioxins.). The lowest dose effects are probably associated with thymic atrophy and decreased immune response, chloracne and related skin lesions, and neoplasia (cancer). Dioxins can cross into the placenta to cause developmental and reproductive effects, decreased prenatal growth, and prenatal mortality. 

Chlorophenoxy compounds have been widely used as herbicides. Agent Orange was a mixture of the chlorophenoxy herbicides 2,4-D (dichlorophenoxyacetic acid) and 2,4,5-T (trichlorophenoxyacetic acid) that also contained small amounts of the highly toxic contaminant TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin see p 184) derived from the process of manufacturing 2,4,5-T. Manufacture ot 2,4-D by chlorination of phenol does not produce TCDD. Populations involved in manufacture or handling of 2,4,5-T may show elevated levels of TCDD on serum testing and overall increased rates of cancer compared to the general population. 

Direct human exposure to dioxin occurred in southern Vietnam and also in Seveso, Italy. It was estimated that southern Vietnam has been contaminated by 160-600kg of dioxin as a result of 80 million liters of defoliant herbicides (Agent Orange, a 50 50 mixture of 2,4,5-T and 2,4-D) being sprayed by the US military over a large area of forests and crops of southern Vietnam from 1962 to 1971 (Westing, 1984 Schecter et al., 2006 ... 

Herbicides may be selective, as for broad-leaved weeds in cereal crops, or unselective, essentially for land clearance. 2,4-Dichlorophenoxyacetic acid (2,4-D), 24.6, was commercialized in the 1940s it is inexpensive, is easy to make, and kills broad-leaved weeds in cereal crops. Worldwide, it is the most widely used herbicide. It is a synthetic auxin, or plant hormone, acting only on dicots and not monocots. There is a whole family of related compounds, prepared from chloroacetic acid (or other halo acids) and various chlorinated phenols. Agent Orange, used as a defoliant in Vietnam in the 1970s, was a 1 1 mixture of 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). The main concerns about its use relate to the possibility that dioxins are formed as contaminants in its manufacture. A few countries ban its use for control of weeds in domestic lawns. 

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