Particles and Mortality: A Clinical Perspective

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Abstract
Increased levels of particulate matter in the air have been associated with increased pulmonary morbidity and mortality in epidemiologic studies. The recent mortality findings are remarkable for the demonstration of an apparent adverse effect of particles in concentration ranges below the present National Ambient Air Quality Standard. This finding warrants consideration in the context of both our understanding of clinical disease and relevant data from toxicologic studies. The elderly and persons with severe chronic obstructive pulmonary disease (COPDJ would be expected to be particularly at risk; causes of acute cardiopulmonary death might be attributed to pulmonary edema, acute respiratory infection, exacerbation of COPD, or perhaps arrhythmias. Available toxicologic studies provide few clues in explaining acute mortality at low particle concentrations. Controlled clinical studies with acidic particles at concentrations greater than 20 times ambient fail to produce a pulmonary inflammatory response in healthy individuals; subJects with COPD, the group at presumably highest risk from the epidemiologic data, show no reduction of lung function with similar acute exposures. Perhaps our understanding of the toxicity of urban particles could be increased by investigations directed at the combined effect of particles with sur-face-complexed metals, particles plus oxidants, sulfuric acid-coated ultrafine metallic particles, or even ultrafine particles alone. Despite the epidemiologic observations, from a clinical perspective the pathophysiologic basis for the excess cardiopulmonary deaths remains problematic; until the findings of new toxicologic studies become available, the framework for interpreting the epidemiologic findings will be inadequate.