symptoms. Symptom reports appear to be sensitive indicators of adverse health effects. The simultaneous use of air monitoring and diary records could reduce the problem of recall bias, and these methods are particularly valuable when small changes in pollutant levels cannot be detected by the subjects in a study. It has been suggested that airborne exposure to low levels of formaldehyde is followed by changes in cells that indicate that the immune system has been affected. Although the precise significance of such changes is unclear, the possibility must be considered that exposure to toxic substances from hazardous-waste dumps causes similar or related changes, as these involve similar exposures. It is likely that air emissions from hazardous-waste sites have caused a variety of symptoms that indicate low-level interference with normal function.
Asthma and other respiratory diseases are common and well-studied disturbances of the respiratory system. During the past decade, our knowledge of factors related to airway responsiveness has expanded greatly. Exposures to a wide range of substances (more than 200 are listed in one review) can change airway responsiveness or reduce the threshold for response to a specific substance. More commonly, exposure leads to a nonspecific increase in airway responsiveness as measured by inhaled histamine or methacholine aerosols. A number of studies of hazardous-waste sites document complaints of chest tightness and shortness of breath. Therefore, the possibility must be entertained that proximity to some of these sites has induced increased airway responsiveness. To our knowledge, this has not yet been specifically sought in hazardous-waste-site studies.
Although the role of ambient air pollution in asthma prevalence has not yet been determined, it seems likely that air pollution is an aggravating factor. It seems unlikely, however, that exposures from hazardous-waste sites could have played a part in the generally increased prevalence of asthma. The role of exposures from hazardous-waste sites in the development of respiratory symptoms cannot be readily evaluated.
As Chapter 5 makes clear, exposure from domestic water is not limited to ingestion, but includes airborne exposures from materials that can outgas during showering, bathing, or cooking, or can be absorbed through the skin. Therefore, estimates of exposure from domestic water need to be expanded to take into account the role of airborne exposures from volatile and nonvolatile substances.