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     Agent Orange was the code name for a herbicide developed for the military, primarily for use in tropical climates. Although the genesis of the product goes back to the 1940's, serious testing for military applications did not begin until early 1960's.

     The purpose of the product was to deny an enemy cover and concealment in dense terrain by defoliating trees and shrubbery where the enemy could hide. The product "Agent Orange" (a code name for the orange band that was used to mark the drums it was stored in, was principally effective against broad-leaf foliage, such as the dense jungle-like terrain found in Southeast Asia.

     The product was tested in Vietnam in the early 1960's, and brought into ever widening use during the height of the war (a067-68),  though it's use was diminished and eventually discontinued in 1971.

     Agent Orange was a 50-50 mix of two chemicals, known conventionally as 2,4,D and 2,4,5,T. The combined product was mixed with kerosene or diesel fuel and dispersed by aircraft, vehicle, and hand spraying. An estimated 19 million gallons of Agent Orange were used in South Vietnam during the war. The earliest health concerns about Agent Orange were about the product's contamination with TCDD, or dioxin. TCDD is one of a family of dioxin, some found in nature, and are causings of the dibenzofurans and PCB's.

     The TCDD found in Agent Orange is thought to be harmful to man, in laboratory tests on animals, TCDD has caused a wide variety of diseases, many of them fatal. TCDD is not found in nature, but rather is a man-made and always unwanted product of the chemical manufacturing process. The Agent Orange used in Vietnam was later found to be extremely contaminated with TCDD.

     The case of the Vietnam Veterans's exposure to dioxin through Agent Orange presents the most complex epidemiological problem ever imagined. The test is this: How do you determine, among 2.5 million Vietnam Veterans, who was exposed to Agent Orange, to what degree and extent, and what if any, is the resultant harm of the exposure?

     Some of the difficulties encountered when confronting this problem include:

1. An estimated 2.5 million men and women served in Vietnam. During their tour or tours, they may have been highly mobile, moving about the countryside throughout an area as big as the state of California. Tracking a single individual for every day of their tour is extraordinarily difficult, tracking large numbers is almost impossible.

2. How can exposure be quantified with precision? "Exposure"  in epidemiology means the person had the "opportunity" for contact in some manner with the chemical. But what is contact? Does this mean direct contact, such as physically being sprayed with the products, or does it include more remote opportunities, such as contact through airborne particles, or contact throughout the food and water chain?

3. Degree of exposure: This is sometimes called the dose/response factor in science. In order to estimate the health effect of an exposure, it is useful (some say critical) to be able to estimate "how much" exposure a person may have had, in quality, frequency, and duration as well as means of exposure.

4. Effect: Science looks for: "cause and effect" in determining health outcomes, It is extremely difficult to accurately state that a behavior or exposure causes an outcome. For example, it is widely accepted that cigarette smoking may cause lung cancer, but this does not account for those who smoke for years and never get cancer, nor those who never smoked and get the disease.

5. Delay: Many diseases, including cancer, have extremely long latency periods. It is possible, therefor, for a person to be exposed to a toxin, and not have the effect of that exposure manifested for twenty years or more. During the years, however, a person may have been "insulted" with other additional exposures through  the workplace or the environment. It becomes extremely difficult assessing and separating there "confounding" exposures when looking for the source of a disease.

     Keeping these difficult criteria in mind, we shall next examine the efforts at studying the effect of Agent Orange exposure.

     The use of herbicides Agricultural research in the quest for synthetic herbicides has been on-going since the 1930's. Classified military research on herbicides took place throughout World War II, primarily at Ft. Dietrich, Maryland. It was not until the 1950's, however that effective herbicides began to be developed (effective in the sense that they would destroy a variety of types of plants).

     The first tests of what was to become Agent Orange (a mixture of the chemicals 2,4,D and 2,4,5,T took place at Camp Drum, New York in 1959. The first operational field tests in Vietnam took place in 1961. Other testing programs were also conducted in Thailand in 1964-65.

     The term "Agent Orange" was at the time; merely one of several used to identify various herbicides used in Vietnam. Others included Agents White, Blue, Purple, Pink and Green. Agent Orange was used in by far the largest quantities in Vietnam.

     The primary service responsible for the application of Agent Orange was the U. S. Air Force, Project "Hades" eventually became Operation Ranch hand, who's motto became "Only we can prevent forest"...

     Most Agent Orange was sprayed from Hercules C-123 Providers, specially equipped with spray booms to spray the herbicide, which was mixed 50-50 with kerosene or diesel fuel for better dispersion. These "fixed wing" missions were carefully recorded on computer tapes known as the 'Herbs Tapes".

     Other spray missions, (particularly near base camp perimeters) were performed by the U. S. Army Chemical Corps, primary from specially equipped UH1 "Huey" helicopters. Spraying from both truck and back pack were utilized along roadways. The Navy also sprayed riverbanks from small PBR-type boats. these spray missions were recorded on computer tapes know as the "service Herbs Tapes".

     The important factor in Agent Orange was its contamination with TCDD or dioxin. the Agent Orange in Vietnam was contaminated in amounts from 0.05 to almost 50 parts per million, with the mean contamination being 2 parts per million (ppm). This contamination resulted in an estimated 368 pounds of dioxin sprayed  over Vietnam over a six-year period.

     The last helicopter spray mission was flown in Vietnam on October 31, 1971




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