April 17, 2003 

“How much dioxin in defoliants sprayed during the Vietnam War?” is probably a tough question without reasonable answers. Up to date, estimates from studies conducted by the U.S. National Academy of Sciences (NAS) (1974) and the U.S. Air Forces (1978), which have been widely accepted, indicate that the total amount of the defoliants sprayed during the Vietnam War was approximately 19.4 million gallons (73.3 million liters) containing between 170 kg and 180 kilograms of dioxin. 

These above estimates, however, are revised upwards by another study conducted by Columbia University in New York for the U.S. Institute of Medicine. Although the study report has not been released, results from the study already appear on the journal Nature, Volume 422 dated April 17, 2003 in an article entitled “The extent and patterns of usage of Agent Orange and other herbicides in Vietnam” by Jeanne Mager Stellman, the primary researcher, and other authors. According to this article, the revised estimates have “...7,131,907 more litres than the ‘uncorrected’ NAS-1974 inventory and 9,440,028 l more than NAS-1974’s ‘corrected’ inventory...” As a result, the total amount of defoliants sprayed during the Vietnam War was estimated by the Stellman study to vary from 80.4 to 82.7 million liters. The Stellman study also indicates that “... the estimate for TCDD [dioxin] present in the spray grows to 221 kg from NAS-1974 estimates of 106-163 kg. Applying 32.8 p.p.m. and 65.5 p.p.m. as the average TCDD in Agents Purple and Pink, we obtain an additional 165 kg, or 366 kg in total...” 

The Stellman study was cited by national broadcasting programs such as ABC’s World News Tonight on April 16, 2003 and dubbed by Declan Butler as “... the most detailed and sophisticated computerized maps ever produced of herbicide spraying in Vietnam” in a story entitled “Vietnam dioxin spray estimate quadruples” dated April 17, 2003 on Nature Science Update at\nsu. The story indicates “A fresh study of long-forgotten flight records of US military aircraft that sprayed Agent Orange over Vietnam has shed unexpected light on one of the darkest episodes of that conflict... For the first time, the authors say, it is possible to calculate an exposure index for individuals and populations that is accurate enough for the epidemiological research that is needed for firm links with health data... The data include flight-path information, the amount and type of agents delivered (including releases caused by leaks, crashes and dumps), troop locations and movements, land features and soil type, and the location of Vietnamese populations... It is possible to tell from the maps, for example, whether individual soldiers or populations were likely to be present in a particular zone on the day of spraying and exposed directly, or whether they arrived later and were exposed indirectly... Using census data for 20,000 Vietnam hamlets for the first time, the study shows that at least 3,000 of them were sprayed directly, affecting between 2 million and 4 million people. The researchers also plan to publish maps of spraying in relation to US troop positions...” 

Those long-forgotten flight records have also shed unexpected light on the “controversial” results of the Stellman study. In fact, if the total sorties, i.e. aircrafts, run between 1961 and 1971 were 19,905 as identified by the Stellman study, the total amount of defoliants sprayed during the Vietnam War can be reasonably estimated at 19,905,000 gallons or 75.2 million liters. That is because the volume of the tank on the plane was 1,000 gallons. This estimate is consistent with 19.4 million gallons or 73.3 million liters estimated by the previous studies. The total amount of defoliants sprayed during the Vietnam War was calculated at 73.7 million liters if the sprayed area of 2,631,297 hectares (estimated by the Stellman study) and the typical rate of 28 liters/hectare were used. The estimate based on parameters from the Stellman study (73.7 million liters) is even closer to the estimate from the previous studies (73.3 million liters). 

We know that each sortie covered a land strip of approximately 253 acres or 101 hectares (240 feet wide and 8.7 miles long). As a result, the sprayed area can be reasonably estimated at 5,035,965 acres or 2,010,405 hectares. The previous estimate of 2.3 million hectares appears to be appropriate because it included areas not sprayed by the Ranch Hand. 

We also know that the defoliants were not used directly. They were mixed with water, jet fuel, or diesel fuel at a ratio varying from 1:10 to 1:50. Therefore, the quantity of dioxin contained in the defoliants sprayed during the Vietnam War should be re-estimated downwards instead of upwards. Because the TCDD concentration in the defoliants was used for estimation, the estimated quantity of dioxin should be at least 10 times less than 366 kg estimated by the Stellman study, i.e. 36.6 kg.  

Because of a lack of data and information, we cannot comment on other issues discussed in the Stellman study at this time. These issues include the dioxin concentration in Agents Purple and Pink (32.8 ppm and 65.5 ppm, respectively), the estimated population (2.1 million to 4.8 million people) that “... were likely to have been sprayed upon directly,” and the land features and soil type used in the study. It appears that the dioxin concentration of Agent Purple is merely the average concentration of 5 (five) samples discussed in the article (17, 22, 33, 47, and 45 ppm). We are making efforts to obtain a copy of the full report of the Stellman study, and we will have additional comments in the near future when such copy is provided. 

 Vietnamese American Science and Technology Society (VAST) NMQ