The Utility of Proximity-Based Herbicide Exposure Assessment in Epidemiologic Studies of Vietnam Veterans (2008) / Chapter Skim
Currently Skimming:
2 The Herbicide Exposure Assessment Model
2 The Herbicide Exposure Assessment Model
Pages 25-34
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 25... ...
. This chapter presents an overview of the exposure assessment concepts underlying measures of exposure opportunity and provides a brief summary of the Stellman team's exposure assessment model and the related software and databases as described in the final report to VA, the journal articles, and presentations by Dr.
|
From page 26... ...
The Stellman team's two measures of exposure opportunity are based on presence at a location that records indicate was within a specified distance of herbicide spraying and can be considered surrogates of exposure. By contrast, many past studies of Vietnam veterans and their health status have used service in Vietnam -- a marker even further removed from dose than the proximity-based measures -- as an exposure surrogate (e.g., CDC, 1987; Breslin et al., 1988; Dalager and Kang, 1997; also see Appendix B)
|
From page 27... ...
For example, such measures may be based on combinations of ambient environmental measurements and individual-level information on behavior patterns that affect exposure; estimates of ambient environmental concentrations derived from fate and transport modeling; or distance and
|
From page 28... ...
Despite their limitations, such relatively crude exposure surrogates as location have been used effectively in many environmental and occupational health studies. Indeed, geographic approaches to exposure assessment can be especially useful when pollutants vary significantly over space in a systematic manner (Briggs, 2003; Colvile et al., 2003)
|
From page 29... ...
The Stellman team has also done extensive work to compile databases on the identification of military units that served in Vietnam and on the location of many units during the period herbicide spraying took place. Data on the location of military units or on the personnel who served in them are essential inputs for generating unit- or person-level exposure opportunity scores, but unlike the geographic parameters or the data on herbicide spraying, these databases are not contained in the herbicide e xposure assessment software.
|
From page 30... ...
The final printing probably will look more like the image on the computer screen. possibility of exposure to residual herbicide from sprays on prior days as "indirect exposure." To calculate the combined direct and indirect EOI, their model takes into account for each spraying mission the quantity of herbicide or concentration factor; the reciprocal distance of the exposure location from the herbicide spray; a time factor, chosen to be a first-order environmental decay of the sprayed herbicide over time; and the concept of continuous dispersion of herbicide all along the path of the flight.
|
From page 31... ...
was developed to facilitate and automate the calculations involved in assessing proximity to the herbicide spraying that is known to have occurred during the Vietnam War. The software, which is accompanied by a manual to guide users, prompts users to provide -- either in a file that can be imported or by directly entering the data -- the information needed to calculate hits or an EOI for individuals or military units of interest.
|
From page 32... ...
UTM refers to the Universal Transverse Mercator map projection, for which latitude and longitude are transformed into meter distances on a projection of the earth's surface onto thin strips running from pole to pole. DoD's version of UTM consists of a two-letter code identifying a particular 100,000-by-100,000-meter grid cell within the map, followed by two three-digit sequences indicating the distance in hundreds of meters east and north, respectively, from the southwest corner of the grid cell.
|
From page 33... ...
. In addition to the data on these stable units, the Stellmans also have created a database capturing location information collected by JSRRC on Army combat battalions serving in the III Corps Tactical Zone during the years 1966–1969, a place and time of intense aerial herbicide spraying (Stellman et al., 2003a)
|
From page 34... ...
2004. Exposure opportunity models for Agent Orange, dioxin, and other military herbicides used in Vietnam, 1961–1971.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.