Công bố mới về Dioxin ở Việt Nam

Công bố mới về Dioxin ở Việt Nam

Đây là công bố mới nhất về dioxin thực tế đã được dùng ở Việt Nam trong chiến tranh. Bài này được công bố trên tạp chí Science hôm 17/4, vì chưa thấy trong này ai nói tới nên mình post lại để tất cả cùng đọc.
The extent and patterns of usage of Agent Orange and other herbicides in VietnamJEANNE MAGER STELLMAN*, STEVEN D. STELLMAN??, RICHARD CHRISTIAN§, TRACY WEBER* & CARRIE TOMASALLO*

* Department of Health Policy and Management, Mailman School of Public Health, Columbia University, 600 West 168th Street, New York, New York 10032, USA
? Department of Epidemiology, Mailman School of Public Health, Columbia University, 600 West 168th Street, New York, New York 10032, USA
? Institute for Cancer Prevention, One Dana Road, Valhalla, New York 10595, USA
§ 2102 Old Stage Road, Alexandria, Virginia 22308, USA


Correspondence and requests for materials should be addressed to J.M.S. (e-mail: jms13@columbia.edu).

Abstract
Herbicides including Agent Orange were sprayed by United States forces for military purposes during the Vietnam War (1961?"1971) at a rate more than an order of magnitude greater than for similar domestic weed control. In 1974, the US National Academy of Sciences published estimates of the extent and distribution of herbicides sprayed. Here we present revised estimates, developed using more-complete data. The spray inventory is expanded by more than seven million litres, in particular with heavily dioxin-contaminated herbicides. Estimates for the amount of dioxin sprayed are almost doubled. Hamlet census data reveal that millions of Vietnamese were likely to have been sprayed upon directly. Our identification of specific military herbicide targets has led to a more coherent understanding of spraying. Common errors in earlier interpretations of the spray data are also discussed.


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(continued)
Between 1961 and 1971 herbicide mixtures, nicknamed by the coloured identification band painted on their 208-litre storage barrels, were used by United States and Republic of Vietnam forces to defoliate forests and mangroves, to clear perimeters of military installations and to destroy 'unfriendly' crops as a tactic for decreasing enemy food supplies1. The best-known mixture was Agent Orange. About 65% of the herbicides contained 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), which was contaminated with varying levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Herbicide mixtures are listed in Table 1.
Table 1 Use of military herbicides in Vietnam (1961?"1971)

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In 1970, the US Congress directed the US Department of Defense (DoD) to engage the National Academy of Sciences to conduct a comprehensive study (NAS-1974) of the ecological and physiological effects of defoliation in Vietnam2. NAS-1974 relied on a chronological record, the HERBS file3, which contained flight path coordinates of Air Force spraying missions carried out between August 1965 and December 1971 and from 1968 on US Army helicopter spraying missions. In 1985, the DoD supplemented this file with the Services-HERBS file, derived from ad***ional record searches. The HERBS file error rate was about 10%, attributable largely to transcription, data entry and pilot recording errors4. Under contract to the NAS, using data more complete than were then available, we undertook, in close collaboration with the US Armed Services Center for Research of Unit Records (CRUR), to correct both files (see Methods) and during this process discovered much ad***ional archived data.
Military herbicide operations in Vietnam became a matter of scientific controversy from their inception5, 6. In April 1970, 2,4,5-T was banned from most US domestic uses, on the basis of evidence of its teratogenicity7. The Agent Orange Act of 1991 requested the Institute of Medicine (IOM) to assess the strength of the evidence for association between exposure to military herbicides and disease in veterans and the feasibility of conducting further epidemiological studies. The IOM recommended that the Department of Veterans Affairs develop historical reconstruction methods for characterizing exposure to herbicides in Vietnam8, 9. The present report is the result of that recommendation.
Background to military use of chemical defoliants
The DoD's Advanced Research Project Agency's (ARPA) Project Agile was instrumental in the US development of herbicides as a military weapon, an undertaking inspired by the successful British use of 2,4,5-T to destroy jungle-grown crops during the insurgency in Malaya. ARPA supported tests on combinations and concentrations of herbicides; calibration studies of the spray delivery system to achieve the desired 28 l ha-1 (3 gallons/acre) rate; and experiments on optimal con***ions to minimize spray drift10. ARPA also developed the Hamlet Evaluation System11 which collected the political census data that we use here for estimating population exposures.
The first large-scale US military defoliation took place in Camp Drum, New York, in 1959, using Agent Purple (a 50:50 mixture of 2,4-D and 2,4,5-T) and a spray system which was the model for those used in Vietnam. Herbicide tests were run from August to December 1961 in the Republic of Vietnam (RVN), using dinoxol and trinoxol12, 13. An insecticide test series was also undertaken. The first major herbicide shipment arrived in RVN in January 1962; defoliation targets were sprayed during September and October 1962 (Agent Purple); crop destruction targets were sprayed in November 1962 (Agent Blue)14. Systematic testing of herbicides and calibration of herbicide delivery systems continued for several years15.
A 1962 pact assigned ownership of the herbicides to RVN when they entered its territory. Vietnamese physically handled the herbicides during off-loading, transport, and transfer to storage tanks. RVN ownership complicated United States Air Force (USAF) logistics and record-keeping, and disposal when Agent Orange use was abandoned in mid-1970 (ref. 16). US policy emphasized that its forces were assisting the RVN in the herbicide programme. C-123 aircraft carried out the missions camouflaged and equipped with removable identification insignias. Crop destruction aircraft bore South Vietnamese markings and were accompanied by a Vietnamese crew member under a State Department/DoD concept known as Farmgate17. Flight crew wore civilian clothing.
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The herbicide targets and US Air Force project folders
US Air Force (USAF) operations, codenamed Operation Ranch Hand, dispersed more than 95% of all herbicides used in Operation Trail Dust, the overall herbicide programme. Other branches of the US armed services and RVN forces, generally using hand sprayers, spray trucks (Buffalo turbines), helicopters and boats, sprayed much smaller quantities of herbicide. Operation Ranch Hand was organized into projects that underwent a complex combined South Vietnamese and US approval system which could sometimes last as long as one year. Each project consisted of specific targets that were often amended or deleted during the approval process. Crop destruction also required White House approval until 1963, after which final approval was delegated to the US Ambassador to the RVN.
We reconstructed the project number to which each mission in the HERBS file belonged by concatenating two data fields. Aggregating missions by project number transforms the HERBS file from a chronological listing of criss-crossing flight paths into target-related groups of flights flown at different points in time (Figs 1 and 2). The importance of projects and targets has not been sufficiently appreciated. NAS-1974, and even the USAF itself18, inverted the hierarchy thus: "All missions within a target formed a project".
Figure 1 Herbicide projects, targets and spraying19. a, Spraying operations were directed at specific targets, 487 of which are shown. Labels in a refer to areas blown up in the corresponding parts of Figs 1 and 2. b, Some areas were targeted in multiple projects at different times: black box, 1964; red boxes, 1965; green boxes, 1966. c, We identified targets active before 1965; at least 4.7 million litres of herbicides were used to destroy 33,339 ha of crops and defoliate 101,300 ha of land. Dioxin contamination may be particularly relevant for this time period. d, Correspondence between HERBS file Agents Orange and White mission paths (orange and white lines) and target boxes, three of which enclose a railroad right-of-way. In Figs 1 and 2, waterways such as canals and rivers are shown in blue.
Figure 2 We could not locate target documentation for half the Ranch Hand missions on the HERBS file. a, Missions clearly directed at specific targets. Our current work is to identify probable targets through such mapping. Colours represent the flight paths of spray missions delivering Agents Orange and White b, HERBS file problem. Some purposes defined in the HERBS file documentation3, such as waterways and communication lines, are often labelled defoliation in the spray tapes, as shown. NAS-1974 and others have analysed spraying by HERBS file purpose but this is inaccurate.

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With US National Archives staff assistance we located a collection of USAF operational project folders for about 50% of the projects and nearly 60% of the volume of herbicide inventoried in the HERBS file19. Many folders contained 'after action reports' or other documentation on completed missions which had not been included in any HERBS file and permitted us to identify some 200 new missions that pre-date August 1965, the date of the earliest missions on the NAS-1974 HERBS file. The early years of the Vietnam War have incorrectly been regarded as of minor importance with regard to herbicide spraying. In total, about 1.9 million litres of Agent Purple were sprayed between 1962 and 1965, which is particularly significant because herbicides manufactured in the early 1960s were almost certainly more heavily TCDD-contaminated than those produced later20. Further, pre-1965 spraying was limited to a relatively small area (Fig. 1c), which thus may be at particular risk for TCDD contamination. Recent data on TCDD residues in soil sampled near US Army Special Forces camps where Agent Purple was sprayed21, and results of soil assays at the testing grid in Eglin Air Force Base, Florida22, support this interpretation.
Revised spray inventory
We have re-estimated the volume and type of herbicides sprayed between 1961 and 1971 to have 7,131,907 more litres than the 'uncorrected' NAS-1974 inventory and 9,440,028 l more than NAS-1974's 'corrected' inventory, in which about 10% of all missions had been discarded because of obvious recording errors. Figure 3 shows the areas sprayed; Fig. 4 shows the yearly distribution of spray; Fig. 5 shows the numbers of sorties flown, 1961â?"1971. Table 2 gives estimates of the frequency with which land areas were repeatedly sprayed.
Figure 3 Volumes of herbicide sprayed. a, b and c represent known volumes of Agents Orange, White and Blue, respectively, sprayed by US military forces in RVN, 1961â?"1971. Volumes are calculated for individual grids spaced at 0.01 degrees (1.2 km2), that divide up Vietnam in a geographic information system developed by us45. Colours in a, b and c correspond to volumes as shown in key. Arrows in a and c point to missions in Laos and in the Parrot's Beak region of Cambodia, respectively. d, Grids sprayed with volumes greater than 4,800 l (about 10% of total), with marker size increasing in proportion to volume and colours corresponding to herbicide codenames. All herbicides containing 2,4,5-T are represented by orange markers.
Figure 4 Litres of herbicides sprayed over 1962â?"1971. The data are taken from the corrected HERBS file and do not include Dinoxol and Trinoxol used in 1961.
Figure 5 Time course of herbicide sorties. At least 19,905 sorties were run between 1961â?"1971 (1â?"34 daily, with a daily average of 10.7 sorties). These data disagree with USAF estimates18. The number of daily sorties mirrors the course of the Vietnam War itself: a slow build-up, maximum activity 1968â?"1969, then a slow but steady decline. The abrupt spraying drop-off at the end of January 1968 corresponds to the Tet Offensive wherein North Vietnamese forces carried out massive, coordinated attacks throughout RVN for nearly 2.5 months. Spray equipment was removed from Ranch Hand aircraft and crew and aircraft participated in airlift operations.
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Contamination of 2,4,5-T with TCDD varied widely by production run, manufacturer, and the percentage 2,4,5-T in the formulation. In early 1966, Agent White, which did not contain 2,4,5-T and hence was not TCDD-contaminated, began to replace Agent Orange. Chemical market forces had led to a shortage of Agent Orange. From a tactical perspective, Agent White was less satisfactory than Agent Orange because several weeks were required for defoliation to begin. It was accepted by the DoD, however, because Agent Orange would apparently no longer be available in sufficient quantities23. Agent Blue was the agent of choice for crop destruction by desiccation throughout the entire War, but more than four million litres of the other agents, primarily containing 2,4,5-T, were also used on crops.
Procurement records show that at least 464,164 l of Agent Pink and 31,026 l of Agent Green, with comparatively higher TCDD levels, were purchased, but we have been able to document little more than 50,000 l as having been sprayed in RVN and about 15,000 l that were used in tests. We have identified missions which dispersed about 1.9 million litres of Agent Purple, but available procurement data show purchase of only 548,100 l (ref. 24), indicating that the procurement records are incomplete.
Extent of dioxin contamination
Estimates of how much TCDD was deposited in Vietnam are based on the volume of 2,4,5-T-containing herbicide sprayed (which has been revised upward on the basis of the new inventory), and on TCDD contamination levels. Estimates of the mean contamination level used by the USAF18 and by NAS-1974 are probably too low. After Agent Orange spraying ended in May 1970, the USAF was required to dispose of very large stockpiles of surplus herbicide that were ultimately incinerated aboard the M/T Vulcanus in 1977. (The US government had also assumed liability for large unblended inventories of 2,4,5-T and 2,4-D from contracted suppliers, either paying for storage or stockpiling the chemicals at Kelly Air Force Base, Texas, in December 1970 (ref. 25). We do not know the fate of the stockpiles.)
TCDD concentrations varied widely in the mixtures. The USAF was required to provide the US Environmental Protection Agency with an Environmental Impact Statement (EIS) prior to incineration26. The EIS sheds light on TCDD levels in the over three million litres of herbicide stockpiled at the Naval Construction Battalion Center (NCBC), Gulfport, Mississippi, and the approximately 26,000 208-litre barrels in the Johnston Island stockpile.
TCDD concentrations ranged from 6.2 to 14.3 p.p.m., and averaged 13.25 p.p.m. in samples drawn for incineration-effluent modelling studies from 28 different NCBC barrels chosen by the USAF as representative of the seven manufacturers of the NCBC stockpile26. However, in other samples drawn from the NCBC stockpile, the TCDD range was about 0.05 to 13.3 p.p.m. (weighted average 1.77 p.p.m.). (NAS-1974, however, calculated a range of <0.05 to 17.0 p.p.m., and an arithmetic mean of 2.99 p.p.m. from the same analytical data2.) The large discrepancies between the effluent modelling study and the other samples analysed by the USAF and NAS-1974 can be explained by information in the background analytical documentation in which runs analysed by NAS-1974 are consistent with the 'low dioxin' analytical series27, 28. The documentation also reports dioxin levels to be heterogeneous, even within production runs. USAF chemists had concluded that generalization from tested barrels to untested ones in the same production batch was not reliable. NAS-1974 appears not to have been provided information either on the heterogeneity of production runs or that they were generalizing from data consistent with a 'low dioxin' analytical series.
Two hundred random samples from the Johnston Island stockpile were also analysed for TCDD content. The Johnston Island stockpile is likely to have been primarily contracted for in 1967 or later and to consist almost exclusively of Agent Orange, because Agents Purple, Pink and Green were not manufactured after the use of Agent Orange began29 and in mid-1966 Ranch Hand missions were curtailed because of a severe herbicide shortage17. NAS-1974 calculated a mean TCDD level of 1.91 p.p.m. 20% for the stockpile2. USAF documentation that is widely viewed as authoritative18, however, disputes this mean and contends that the four highest values (17, 22, 33 and 47 p.p.m.) must have been Agent Purple, and not Agent Orange, because these values exceeded the mean reported for the NCBC inventory, citing a personal communication from a military officer who recalled that as many as 20 drums of Agent Purple may have been present in the stockpile and redrummed into Agent Orange containers. (The hypergeometric probability of selecting four of the 20 Agent Purple drums from the stockpile is 1.32 10-5.) In fact, the range observed is completely consistent with the USAF's own analysis of the range and heterogeneity of TCDD levels27, 28. By 1988, Young, the senior author of the USAF documentation, dropped the word "may" and simply reported the four high values to have been Agent Purple30. This latter reference has been relied upon as authoritative by the IOM8, and many others.
A 1971 NAS-1974 analysis of six core soil samples collected from the central calibration grid at Pran Buri, Thailand, over which all ARPA test flights had flown, found TCDD levels ranging from non-detectable (<0.0012 p.p.m.) to 0.0233 p.p.m. and 2,4,5-T residue from non-detectable (< 0.02 p.p.m.) to 0.61 p.p.m.. NAS-1974 estimated the original herbicide to have contained <3 to 50 p.p.m. TCDD, consistent with the range observed in the Johnston Island stockpile2. (The USAF documentation18 incorrectly asserts that NAS-1974 had erred in attributing the TCDD to Agent Orange rather than to Agents Purple and Pink. These misstated findings are used as further rationale for assuming the four high TCDD values to have been Agent Purple.)
Although Agent Purple is, indeed, likely to have been more highly contaminated with TCDD (an archived sample of Agent Purple at Eglin Air Force Base contained 45 p.p.m. TCDD18 and historical TCDD contamination data show early 1960s contamination levels to have been much higher)20, it is also likely that mean TCDD levels in Agent Orange were far higher than 3 p.p.m. for much of the herbicide used. An average value closer to 13 p.p.m. may be more realistic.
If 3 p.p.m., the mean associated with the 'low dioxin' series is conservatively applied to the new inventory we have presented here, the estimate for TCDD present in the spray grows to 221 kg from NAS-1974 estimates of 106â?"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 ad***ional 165 kg, or 366 kg in total (which still does not take into account the herbicides sprayed by RVN forces, and possibly by US Army and Navy forces by trucks, boats, hand sprayers and helicopters, nor the more than 400,000 l of Agent Pink shown in procurement records but not found in any recorded missions). If, indeed, dioxin contamination of Agent Orange could be fourfold or more higher, then this increased dioxin load grows proportionally. It is also possible that some missions recorded as having dispersed Agent Orange did, in fact, spray the much more highly contaminated but unaccounted-for Agent Pink, but we know of no way to determine this. It is more likely that the unaccounted-for herbicides were used by Vietnamese troops, although about 50,000 l of Agent Pink do appear on the 1965 inventory.
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Estimates of population exposure to herbicides
A Hamlet Evaluation System (HES) in which US district advisors and Vietnamese district chiefs filled out monthly political survey and census forms was established in June 1967 and a gazetteer of place names and precise geographical locations was also created. The HES data provide a comprehensive rural census that permits us to estimate the numbers of hamlets and size of the population directly sprayed upon31. HES files were not made available to NAS-1974 early enough to permit analyses2.
More than 20,585 unique hamlets are represented in the corrected version of the database used here. Population data are not available for 18% of these hamlets and population data are not systematically reported each month for all years. Among the hamlets with some population data, 3,181 were sprayed directly and at least 2.1 million but perhaps as many as 4.8 million people would have been present during the spraying. Another 1,430 hamlets were also sprayed, but we cannot estimate the population involved. In all, at least 3,851 out of 5,958 known fixed-wing missions had flight paths directly over the hamlet coordinates given in the HES and gazetteer data and about 35% of the total herbicide sprayed was flown by these missions, although, in general, flight paths extended beyond hamlet borders.
Aborted missions and emergency dumps
Forty-two missions originally intended to spray 120,000 l of herbicide are known to have ended with emergency herbicide dumps where the chemical was jettisoned in about 30 s, compared to the usual 4 to 5 min. At least five herbicide-loaded aircraft crashed. Hundreds of other missions were aborted after take-off because of poor weather at the target site, heavy anti-aircraft fire, or mechanical problems. Such aircraft returned to base with herbicide load intact. It has been erroneously reported that aborted missions automatically dumped herbicide before landing32. Many flights were 'aborted' before take-off because of mechanical problems. One extensive but incomplete list of aborted missions is contained in a large-format uncorrected version of the HERBS file, known as the Map Book, which has served as the basis for much analysis of potential exposure, particularly by Vietnamese scientists33. When the Map Book list is checked against the USAF Daily Air Activities Reports (DAARS), it is found to consist primarily of mechanical aborts, not herbicide dumps. Conversely, the list does not contain many actual dumps identified by CRUR and has other inaccuracies which have been corrected over the years by the DoD and now by us.
In 1971, NAS-1974 analysed five soil samples from an area in which about 3700 l of Agent Orange had been dumped in December 1968. No 2,4,5-T could be detected. TCDD was not analysed34. Aborted missions may not represent the significant source of exposure that it has been represented to be by others, and studies which have relied on the uncorrected data in the Map Book will, of necessity, be inaccurate.
Discarded drums
Approximately two litres of herbicide residue remains in the 208-litre barrel after it has been 'emptied'. Typically about 20% of the residue remains after three rinses. Residue, on average, contained 5.96 mg of TCDD, arising from heavily contaminated herbicides and about 1.25 mg per drum from 'low dioxin' herbicides26. Barrel residues had led to inadvertent defoliation of trees and gardens in Da Nang, Nha Trang, Bien Hoa, Phu Cat and Saigon civilian areas near USAF airbases that handled the herbicides when the empty barrels were transported to local merchants for commercial uses35. Improved handling procedures were adopted in 1969 following the Da Nang defoliation incident but the ultimate fate of most of the empty barrels is not known and the extent to which people who used the barrels for other purposes may have been exposed is not known.
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Spraying in Laos and Cambodia
Operation Ranch Hand flew its first missions outside RVN in December 1965 to defoliate the major reinforcement and supply route through Laos known as the 'Ho Chi Minh trail'. Known spraying was above the 17th parallel (the northern border of RVN), along Routes 92, 922, 96 and 965 below Tchpone and the Sihanouk Trail that went from Laos to Cambodia. Missions in both countries below the 17th parallel can clearly be seen in Fig. 3a and c. A small amount of crop destruction using Agent Blue was also documented. Laos was also the site of a brief experiment to determine whether F-4E Phantom II jet fighters could successfully be used to carry out spray operations and avoid anti-aircraft fire. At least five F-4E missions were flown until a fighter was shot down and the strategy was abandoned. Documentation of spray activities in Laos is incomplete. The Services-HERBS file shows flight paths for 210 missions, which sprayed about 1.8 million litres. NARA-held documentation shows as much as 14% more herbicides as having been sprayed but no coordinates are given so that these data cannot be included in the revised HERBS file36.
Unlike in Laos, it was official US policy to avoid spraying Cambodia either directly or indirectly by spray drift37 (cited by Cecil38). Records show several heavily sprayed regions of RVN, near Cambodia. The HERBS file shows one five-aircraft Ranch Hand mission dispersing approximately 19,000 l of Agent Orange on 5 April 1969 inside Cambodia. Another nine missions dispersed about 136,000 l of Agent Orange while partly over Cambodian territory (Fig. 3c). At the typical rate of 28 l ha-1 this would cover about 5,500 ha. Undocumented spray drift may have also occurred. In May 1969 a diplomatic crisis arose when Cambodia charged the US with repeatedly spraying it and defoliating 70,930 ha; evidence of defoliation was confirmed by visiting foreign scientists39. Cambodian claims seem to be exaggerated in that to achieve the extent of alleged defoliation nearly half of the Ranch Hand flights for Aprilâ?"May 1969 would have to have been directed towards Cambodia. Records are not available to resolve the controversy, particularly since the area was devastated by US B-52 bombing raids in 1970.
Discussion
The Vietnam War ended in 1975, yet no large-scale epidemiological study of herbicides and the health of either the Vietnamese population or war veterans has been carried out. Discussions of health and ecology studies in Vietnam have recently taken place40. During the course of developing an exposure methodology, we have unexpectedly come upon primary data which expanded existing herbicide spraying databases and could help guide the design of human health and of environmental studies.
NAS-1974 found the HERBS file to be a powerful tool for studying exposure to herbicides. The concordance between HERBS file mission coordinates, operational folders, and the precise locations of roadways, rail lines, power lines, canals and so on given in modern mapping software increases our confidence in the HERBS file. Viewing the HERBS file as a carefully planned target-based military exercise, rather than chronological unrelated missions criss-crossing RVN in straight-line paths affords a coherent analytical approach.
Our analyses using original operational records raise questions about the spraying data and dioxin contamination relied upon by researchers and policymakers. For example, we find that the '202 Tasks Realized' document used by NAS-1974 assumed missions that are missing from the HERBS file41 to represent targeted areas and anticipated spraying rather than operations completed. (Further, the '202 Tasks Realized' document contains many errors, such as misplaced decimal points for subtotals of volume sprayed, which cumulate and greatly exaggerate the total volume)42. Therefore, some NAS-1974 estimates of 'missing' spray must be revised downward. On the other hand, dioxin contamination estimates should be revised upward. Comparatively small amounts of Agent Purple and Pink sprayed in Vietnam between 1961â?"1965 may have deposited a large percentage of the total dioxin.
Large numbers of Vietnamese civilians appear to have been directly exposed to herbicidal agents, some of which were sprayed at levels at least an order of magnitude greater than for similar US domestic purposes20. Other analyses being carried out by us show large numbers of American troops also to have been directly exposed or to have served in recently sprayed areas. Areas sprayed during the early years and in the various test sites around the world15 may be of particular interest for follow-up ecological and epidemiological studies.
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Methods
We constructed a new version of the HERBS file using operational records for the USAF 12th Air Commando Squadron (ACS), which carried out the Ranch Hand missions and by systematic comparisons of four different versions of the herbicides files found at the US National Archives43 and the active file at CRUR. Of 18,087 mission records there were 1,264 non-matches between HERB2REV and the current CRUR file (that is, 2.5 million litres out of more than 66.6 million litres). About 3.4% of the total volume is represented at CRUR but not the other files. We also identified errors by mapping flight paths and by consistency checking (for example, legs that were very short or very long, over water, and so on). Discrepancies which we could not thus resolve were reviewed by a small panel of experts. The same panel reviewed each proposed amendment to the HERBS file. A small number of missions which remained ambiguous were discarded. All discarded missions were from the Services-HERBS.
Flight paths for 65 missions of fixed-wing aircraft missions that had been represented in the original HERBS file only by a single point (usually the calculated centre-of-mass) were readily deduced by comparison with similar missions or known targets. (Some missions are correctly represented as single points because they document perimeter spraying carried out by spraying specific discrete points, such as outside base camps near guard posts.) The revised file contains 9,141 missions, primarily by air, but also using other means of delivery.
We used digitizing software44 to derive the longitudes and latitudes defining the target perimeters from hand-drawn maps in the USAF Project Folders19. For folders with no map we extracted the Universal Transverse Mercator (UTM) coordinates from written descriptions of the targets and entered them into a Geographic Information System (GIS) which we created45, similar to a databank model created by NAS-1974 (we are willing to assist researchers in using our GIS software for estimating exposure using these data). Population and hamlet exposure estimates used data contained in the HES and Vietnam gazetteer data files31. Each hamlet location was assigned a grid identifier and proximity to spray was calculated using our GIS system software.
Received 6 December 2002;accepted 4 March 2003
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Acknowledgements. This research was supported by the National Academy of Sciences, the Department of Veterans Affairs and USPHS at the National Cancer Institute. We thank D. Hakenson and his staff at the US Armed Services Center for Research of Unit Records for technical support and access to military records; the staff of the National Archives and Records Administration, particularly R. Boylan and M. O. Adams; N. Heim for assistance with illustrations and F. Benjamin for assistance with military records. R.C. is a retired member of the US Army.
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Vietnam dioxin spray estimate quadruples
Flight records reveal full extent of Agent Orange contamination.
17 April 2003
DECLAN BUTLER
This story is from the News section of the journal Nature

The health effects of the herbicides spread during the war are still unclear.
â alamy.com


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.
The study1 revises previous estimates of the quantity of the herbicide sprayed during the Vietnam War sharply upwards. Together with the earlier use of other herbicides - known as Agent Purple and Agent Pink - it finds that the total amount of dioxin contaminant sprayed in the war was up to four times as great as was previously estimated.
And in a report due to be released on 17 April, the US Institute of Medicine declares that the new work shows that it is feasible to perform large-scale epidemiological studies of the links between the herbicide spraying and the health of the Vietnamese population and US veterans. The institute calls on the US government *****pport such studies.
The new analysis, performed by a group led by Jeanne Mager Stellman at Columbia University in New York, provides the most detailed and sophisticated computerized maps ever produced of herbicide spraying in Vietnam. 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.
Stellman's team calculated the index by compiling a computer database that overlays staggering amounts of various data, much of it newly unearthed, onto geographical coordinates. 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.
"I just think, 'Wow', if only this had been around earlier," says Alistair Hay, an environmental toxicologist at the University of Leeds, UK. "It fills in the gaps, giving an accurate and comprehensive picture of where spraying took place."
Like a widely cited 1974 National Academy of Sciences study on Agent Orange, the researchers relied heavily on HERBS, an electronic record compiled by the US military, which includes data on flight paths, herbicide agents and volumes used, and other information on 10,000 spraying missions. But when digging out and cleaning up these data, the team stumbled on valuable archive data that had been overlooked, and discovered a connection that allowed them to extract far more information from existing records.
A major shortcoming of earlier analyses using HERBS was that its spraying data were treated chronologically, leading to mission flight paths criss-crossing the country but without showing patterns of which areas were sprayed over time. The new study's breakthough came when Stellman, browsing army archives, found another source of information: the daily logs filed by pilots after missions. "It was a sort of 'eureka moment' when I realized that there were 'project' numbers on each of these reports, and that those numbers vaguely resembled a couple of columns that we have never put together before or used," she says. "I just thought, 'Oh my God, look at this!'."
These columns of numbers included a column called 'missionnum', which, when linked with data in the 'military region' column, matched up with project numbers kept in the pilots' logs. The logs contained exactly what HERBS lacked: details of the missions' targets. The link enabled the team to draw the first maps of spraying patterns in Vietnam that show precise localized target zones, and how much herbicide was sprayed on them and when.
It fills in the gaps, giving an accurate and comprehensive picture of where spraying
took place
Alistair Hay
University of Leeds


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.
The findings are set to provoke a vigorous reaction both from US veterans' groups - some of which are still seeking compensation for exposure to Agent Orange - and the Vietnamese government. 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.
The model used in the study is "a valid means for assessing wartime herbicide exposure in Vietnam veterans", says the Institute of Medicine report, written by a committee chaired by David Hoel, an epidemiologist at the Medical University of South Carolina in Charleston. It commends the team for its "dogged pursuit of historical records" and recommends that the Department of Veterans Affairs, which funded the study, work with other government agencies *****pport new epidemiological studies of veterans' health.
Declan Butler is European Correspondent for the journal Nature


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

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