Agent Orange and Other Herbicides

Exposures to TCDD also resulted from industrial wastes or accidents that contaminated entire communities such as Times Beach, Missouri, and Seveso, Italy. Although TCDD is no longer commercially available, it remains a hazard for several occupations and occupants of certain geographical localities (Table 1-5). Cocaine abusers can encounter cocaine derived from coca plants treated with phenoxy herbicides in countries without herbicide regulation (Elsohly et al. 1984). 

TABLE 1-5. Occupations and locations at risk for herbicide poisoning 

Occupations Firefighters (transformer/capacitor fires) Hazardous waste cleanup crews Manufacturers of chlorinated herbicides, germicides, and organic solvents Municipal/waste incinerator workers Utility workers working in or spraying herbicides along rights-of-way Vietnam War veterans 

Residence Herbicide-sprayed utility or other right-of-way Municipal/waste incinerators Other agricultural spraying areas 

Others Breast-fed children of exposed women Cocaine users 

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Stellman, J.M., Stellman, S.D., Christian, R., Weber, T., Tomasallo, C., 2003. The extent and patterns of usage of Agent Orange and other herbicides in Vietnam. Nature 422, 681-687. 

We should not forget that pesticides have been used as warfare agents, notably in Vietnam. The use of Agent Orange and other herbicides had an immediate and chronic effect on human health, and the vegetation has been seriously and permanently disturbed (Westing, 1975). 

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. 

Herbicides are designed to kill plants, not animals, and in general have lower mammalian toxicity than insecticides. Most herbicides interfere with plant hormones or enzymes that do not have any direct counterpart in animals. The most serious human health concerns have been related to contaminants of the primary chemical herbicide. There is an enormous amount of animal and some human toxicity data on 2,4-D and 2,4,5-T, but it now appears that much of this toxicity is caused by the contaminant TCDD. Military personnel exposed to Agent Orange, often contaminated with TCDD, reported birth defects, cancers, liver disease, and other illness. These concerns led to improvement in the manufacturing process to reduce TCDD contamination and ultimately to a reduction in use of 2,4-D herbicides. There is also concern that some herbicides may affect wildlife. For example, atrazine, a persistent herbicide, may adversely affect frogs. Persistence of herbicides may also... 

Dioxins are sometimes—but rarely—produced in nature, most commonly during volcanic eruptions and forest fires. Their most common source in the environment are industrial reactions in which they occur as by-products of other chemical changes or during the incineration of certain synthetic organic compounds. For example, trace amounts of 2,3,7,8-TCDD occur as an impurity in the herbicide Agent Orange (a mixture of 2,4,5-trichlorophenoxyacetic acid [2,4,5-T] and 2,4-dichlorophenoxyacetic acid [2,4-D]), which was... 

Chance almost certainly explains the difference in the occurrence of the neural tube defects, as it explains many other results in epidemiology. For instance, many early studies of possible effects from exposures to herbicides reported increases in cleft lip and cleft palate (none of which was considered significant)43 among children born to exposed parents. In contrast, there were five cases of cleft lip and cleft palate among the children bom to the Comparisons and none in the children born to Ranch Hands. No one would argue that Agent Orange prevents cleft lip and palate based on this observation. 

IOM produced two volumes about Agent Orange in 2000. One is a special report about herbicides and diabetes. The other is an update that added a childhood cancer to the list of diseases caused by parental exposures to herbicides. 

A legacy of the use of an estimated 600 kg of the herbicide Agent Orange during the conflict in Vietnam has been the contamination of soil, rivers, sediment and biota with dioxins [53, 54]. Hot spots of contaminated soils in the Aluoi Valley and other former US bases where the pesticides were stored have recently been identified [53]. These sites have considerably higher dioxin levels compared with regions where dioxins were aerially sprayed. These sites, if not cleaned up, will be a continued source of dioxins to the local environment for the foreseeable future. 

In addition, a morbidity study was recently completed (Ranch Hand study) on pilots who flew spraying missions in Vietnam and on other Air Force personnel. These members of the military were exposed to Agent Orange, a mixture of the herbicides 2,4-D and 2,... 

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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