A Geographic Information System for Characterizing Exposure to Agent Orange and Other Herbicides in Vietnam. (Research)

By Stellman, Jeanne M.; Stellman, Steven D. et al. | Environmental Health Perspectives, March 2003 | Go to article overview

A Geographic Information System for Characterizing Exposure to Agent Orange and Other Herbicides in Vietnam. (Research)


Stellman, Jeanne M., Stellman, Steven D., Weber, Tracy, Tomasallo, Carrie, Stellman, Andrew B., Christian, Richard, Jr., Environmental Health Perspectives


Between 1961 and 1971, U.S. military forces dispersed more than 19 million gallons of phenoxy and other herbicidal agents in the Republic of Vietnam, including more than 12 million gallons of dioxin-contaminated Agent Orange, yet only comparatively limited epidemiologic and environmental research has been carried out on the distribution and health effects of this contamination. As part of a response to a National Academy of Sciences' request for development of exposure methodologies for carrying out epidemiologic research, a conceptual framework for estimating exposure opportunity to herbicides and a geographic information system (GIS) have been developed. The GIS is based on a relational database system that integrates extensive data resources on dispersal of herbicides (e.g., HERBS records of Ranch Hand aircraft flight paths, gallonage, and chemical agent), locations of military units and bases, dynamic movement of combat troops in Vietnam, and locations of civilian population centers. The GIS can provide a variety of proximity counts for exposure to 9,141 herbicide application missions. In addition, the GIS can be used to generate a quantitative exposure opportunity index that accounts for quantity of herbicide sprayed, distance, and environmental decay of a toxic factor such as dioxin, and is flexible enough to permit substitution of other mathematical exposure models by the user. The GIS thus provides a basis for estimation of herbicide exposure for use in large-scale epidemiologic studies. To facilitate widespread use of the GIS, a user-friendly software package was developed to permit researchers to assign exposure opportunity indexes to troops, locations, or individuals. Key words: Agent Orange, cacodylic acid, defoliants, 2,4-dichlorophenoxy acetic acid, exposure opportunity, geographic information system, GIS, herbicides, military, picloram, 2,4,5-trichlorophenoxy acetic acid, Vietnam.

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Between 1961 and 1971, the United States Armed Forces in South Vietnam used nearly 19.5 million gallons of chemical herbicides for tactical defoliation and crop destruction. Several types and combinations of chemicals were used. The mixtures were nicknamed by the color of the identification stripe that appeared on their chemical storage drums (National Research Council 1974). The three most common mixtures were Agent Orange [esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)], Agent White (triisopropanolamine salts of 2,4-D and picloram), and an arsenical called Agent Blue (cacodylic acid). It has been estimated that Agent Orange was contaminated with < 0.05-100 ppm of dioxin (Darrow 1971). The U.S. Air Force in its Operation Ranch Hand dispersed between 97% and 98% of all the herbicides used. Figure 1 shows a typical Ranch Hand mission composed of three C-123 aircraft (each known as a "sortie") flying in typical tight formation and usually spraying at an altitude of 150 feet. Spraying was only carried out in clear weather, with wind speeds less than 8-10 knots and no temperature inversion present.

[FIGURE 1 OMITTED]

An estimated 3.2 million American men and women served in the Armed Forces in Vietnam, many of whom were assigned to areas defoliated by herbicides such as Agent Orange (Stellman et al. 1988a). Neither the extent of exposure nor long-range health effects are fully known after 30 years. The Agent Orange Act of 1991 (P.L. 102-4) directed the Secretary of Veterans Affairs to request that the National Academy of Sciences (NAS) conduct a comprehensive review and evaluation of available scientific and medical information about the health effects of Agent Orange and other herbicides. The Academy convened a committee of experts at the Institute of Medicine (IOM), which since 1994 has issued biennial reports that have associated a number of veteran illnesses with herbicide exposure, based on data drawn primarily from nonveteran observations (IOM 1994, 1996, 1998, 2001). …

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