Advances in molecular biology and analytical chemistry are providing potentially useful tools for the epidemiologic study of occupational and environmental lung disease (NRC, 1989; Paoletti, 1995; Schulte, 1996). These tools are biological indicators, or biomarkers, of events that represent exposure to a xenobiotic, effects of exposure and susceptibility to effects of exposure. Taken together, these biomarkers can be used to describe a continuum of events following a xenobiotic exposure and proceeding through resultant diseases. Using a continuum concept expands the classic epidemiologic model that involves statistically inferring an association between an exposure and disease. This classic approach has yielded many useful findings for public and occupational health with regard to pulmonary diseases such as coal workers' pneumoconiosis, beryllium disease, asthma from wood dust and lung cancer from asbestos, cigarette smoking, bis-chloromethyl- ether and uranium. The epidemiologic assessment involving these lung diseases generally relied on statistical inference rather than mechanistic insight to associate exposure with disease; but that is not to say that investigators conducting such studies lacked biological hypotheses for such associations. What differs from these previous investigations is the potential for identifying various events in a continuum between an exposure and disease (NRC, 1989). These events are represented by biomarkers. Biomarkers are generally biological measurements representing or correlating with an event, serving as the event, or predicting the event. Biomarkers can range from those on the macroscale, such as dysfunction, disease and death down to those on the microscale (such as the cell, gene or molecule). The middle of this range can include biomarkers such as various anatomic, physiologic and functional changes.
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