Steven Stellman - Exposure opportunity models for Agent Orange, dioxin, and other military herbicides used in Vietnam, 1961-1971

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      Stellman, S. D., Stellman, J. M. 14 (4) 354-62-

      Abstract: Nearly 19.5 million gallons of   herbicides were sprayed on the Republic of Vietnam between 1961   and 1971 for military purposes. Amounts of spray and patterns of   applications are available in an electronic file called HERBS   that contains records of 9141 defoliation missions, including   detailed coordinates of US Air Force Ranch Hand aircraft flight   paths, along with chemical agent and gallonage sprayed. Two   classes of models for use in epidemiological and environmental   studies that utilize the HERBS data for estimating relative   exposure opportunity indices are presented: a discrete "hits"   model that counts instances of proximity in time and space to   known herbicide applications, and a continuous exposure   opportunity index, E4, that takes into account type and amount of   herbicide sprayed, distance from spray application, and time   interval when exposure may have occurred. Both direct spraying   and indirect exposure to herbicide (or dioxin) that may have   remained in the local environment are considered, using a   conservative first-order model for environmental disappearance. A   correction factor for dermal versus respiratory routes of entry   has been incorporated. E4 has a log-normal distribution that   spans six orders of magnitude, thus providing a substantial   amount of discrimination between sprayed and unsprayed areas. The   models improve on earlier ones by making full use of the geometry   of the HERBS spray flight paths of Ranch Hand aircraft. To the   extent possible so many decades after the War, the models have   been qualitatively validated by comparison with recent dioxin   soil and biota samples from heavily contaminated areas of   Vietnam, and quantitatively validated against adipose dioxin   obtained in epidemiological studies of Vietnamese. These models   are incorporated within a geographic information system (GIS)   that may be used, as one would expect, to identify locations such   as hamlets, villages, and military installations sprayed by   herbicide. In a novel application, the GIS also facilitates   quantitative risk assessment in epidemiological and ecological   studies by applying the models within a framework of historical   reconstruction of exposure history of individuals based upon   their location histories.

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