in the health outcomes chapters from endpoint to endpoint, and also from update to update. Of particular importance to the VAO project are a number of continuing studies of populations that have been exposed to the herbicides sprayed in Vietnam or to their components. It is essential that laboriously amassed information on a single population be recognized as such. Placing each new publication in historical context helps the committee avoid factoring what is actually a single observation into their deliberations repeatedly. Such studies are extremely important in describing the time course of a population’s response to an exposure. Furthermore, joint consideration of an entire body of research on a population may permit more insightful evaluation of relationships with potential confounding factors. This chapter augments the existing information on these study populations with descriptions of any new publications investigating any of their members, explaining how the new work meshes with earlier efforts.
Many studies, particularly cancer cohort studies, report on multiple health endpoints. The weight appropriately attributed to a study’s findings is determined in the context of its design and execution. Because repetition of this information in the health outcomes chapters for every specific endpoint report would be cumbersome and tedious, discussions of design and evaluation comments for these studies are presented in this chapter and distilled in the design tables in Appendix A. Of course, a multi-endpoint study might also qualify for inclusion in this chapter because it addresses a previously studied population.
Studies new to this update that report on a single endpoint and were conducted on a population that has not been studied by others are not included in this chapter. Their designs characteristics are present in the one place where their results are reported in one of the chapters on health outcomes.
The chapter is organized into three major sections—occupational studies, environmental studies, and studies of Vietnam veterans. Detailed descriptions of many of the study populations can be found in Chapter 2 of the original report of this committee, Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (hereafter referred to as VAO; IOM, 1994), and the criteria for inclusion in the review are discussed in Appendix A of that report. In addition to a review of studies that involved exposures to the chemicals of interest (2,4-D; 2,4,5-T and its contaminant TCDD; cacodylic acid; and picloram), the committee also examined some studies that addressed compounds chemically related to the herbicides used in Vietnam, such as 2-methyl-4-chlorophenoxyacetic acid, hexachlorophene, and chlorophenols, including trichlorophenol. In some published reports, the study investigators did not indicate the specific herbicides to which study participants were exposed or the magnitude of exposure; those complicating factors were considered when the committee weighed the relevance of a study. Available details of exposure assessment and use of exposure in analyses are discussed in Chapter 5.
The occupational section covers studies of production workers, agriculture and forestry workers (including herbicide and pesticide appliers), and paper and