are limited by the quality of exposure data and to various extents by the low size of their populations, particularly if such rare outcomes as childhood leukemia and congenital defects are being addressed. Even if the different routes of exposure—inhalation vs ingestion—are recognized, the occupational studies tend to dominate the evidence. The committee has incorporated the information from solvent water-contamination studies, as warranted, into the overall assessments of the epidemiologic evidence as reflected in the tables and categorization of evidence in Chapter 5 and focuses here on any special contributions as a function of the more direct relevance of water contamination as the source of exposure.
With regard to methods, the studies in this chapter have largely started with the conventional approach of characterizing a broad geographic area and period and relating health outcomes to estimated exposure. However, several have gone further in refining the exposure estimates by using sophisticated engineering models (particularly in Woburn, Massachusetts) in ways that are broadly applicable to the situation at Camp Lejeune. Similarly, the Cape Cod studies have gone beyond routinely available information on water source to estimate delivered dose.
The strategy pursued by Reif et al. (2003) and in the series of Santa Clara, California, studies (for example, Wrensch et al. 1990) also warrants consideration. They began with an episode of environmental contamination but proceeded to conduct individual data collection with interviews, medical records, and, in the case of the Denver, Colorado, episode, direct evaluation of potentially affected individuals. Available records have merit as a starting point, but for many health outcomes of interest it is essential to go further to collect new data.
Collectively, the epidemiologic studies of solvent contamination of water supplies and adverse health effects are of limited quality. If their distinctive strengths and limitations are taken into account, such studies contribute to the overall assessment of the epidemiologic literature, but the committee has judged that their strengths (comparability with Camp Lejeune in exposure pathways and diversity of exposed population) do not overcome their limitations (especially quality of exposure assessment, lower range of exposure, and imprecision in measures of association) to allow identification of high-priority outcomes on the basis of their results alone.