of hazardous wastes, and they include long-term studies of actively exposed persons, prospective studies of a distinct group, and followup studies of exposed children. Here, problems of execution relate to the emotional turmoil that usually surrounds suspicion of exposure to hazardous wastes, the difficulty of following residents who might have moved away, and the climate of distrust that sometimes arises after the discovery of a hazardous-waste site. In addition, because the courts often seal resolved lawsuits, potentially valuable information on long-term consequences of exposure is unavailable for scientific review and analysis. The committee's second report will discuss this further.

Although few studies directly assess airborne exposures to hazardous wastes, the committee finds persuasive evidence that health effects can occur from such exposures. Review of the relevant animal literature on compounds known to occur at hazardous-waste sites, along with the few epidemiologic studies, shows that a wide range of effects may occur, including such serious diseases as cancer, birth defects, and neurologic disease. Studies of populations near hazardous-waste sites have detected complaints of neurobehavioral symptoms. Although it might be concluded that recall bias explains the differences in such subjectively reported symptoms, the real possibility nevertheless exists that the symptoms complained of are more sensitive as indicators of significant exposure than are more severe diseases that have long latencies, such as cancer and other chronic diseases.

The constellation of self-reported symptoms in persons living near some hazardous-waste sites shows remarkable consistency in populations with similar exposures in different countries. These symptoms have recently been provoked in double blinded tests using subjects who might or might not have previously reported symptoms. Those exposed to odorless test agents developed neurobehavioral symptoms, further strengthening the argument that there is a physiologic basis to some of the complaints.

Symptom reports appear to be sensitive indicators of adverse health effects. Simultaneous use of air monitoring and diary records could reduce the problem of recall bias, which is especially troubling in situations where people suspect ill effects could be produced by their exposures. These methods are particularly valuable when small changes in pollutant levels cannot be detected by the subjects in a study. The committee believes that further studies of acute symptoms linked to monitoring data, based on concurrent exposure measurements, are likely to reveal that reported symptoms are not completely explained by recall bias. The current data base clearly indicates the importance of continued use of these techniques.

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