Air Pollution and Retained Particles in the Lung. (Articles)

Article excerpt

Epidemiologic evidence associates particulate air pollution with cardiopulmonary morbidity and mortality. The biological mechanisms underlying these associations and the relationship between ambient levels and retained particles in the lung remain uncertain. We examined the parenchymal particle content of 11 autopsy lungs from never-smoking female residents of Mexico City, a region with high ambient particle levels [3-year mean P[M.sub.10] (particulate matter [less than or equal to] 10 [micro]m in aero dynamic diameter)= 66 [micro]g/[m.sup.3]], and 11 control residents of Vancouver, British Columbia, Canada, a region with relatively low levels (3-year mean P[M.sub.10] = 14 [micro]g/[m.sub.3]). Autopsy lungs were dissolved in bleach and particles were identified and counted by analytical electron microscopy. Total particle concentrations in the Mexico City lungs were significantly higher [geometric mean = 2,055 (geometric SD = 3.9) x [10.sup.6] particles/g dry lung vs. 279 (1.8) x [10.sup.6] particles/g dry lung] than in lungs from Vancouver residents. Lungs from Mexico City contained numerous chain-aggregated masses of ultrafine carbonaceous spheres, some of which contained sulfur, and aggregates of ultrafine aluminum silicate. These aggregates made up an average of 25% of the total particles by count in the lungs from Mexico City, but were only rarely seen in lungs from Vancouver. These observations indicate for the first time that residence in a region with high levels of ambient particles results in pulmonary retention of large quantities of fine and ultrafine particle aggregates, some of which appear to be combustion products. Key words: air pollution, environmental exposure, particles, pulmonary retention. Environ Health Perspect 109:1039-1043 (2001). [Online 27 September 2001]


Epidemiologic studies indicate that current levels of particulate air pollution are associated with adverse health outcomes, including increased cardiopulmonary mortality (1,2). Although evidence suggests that short-term impacts of particulate air pollution are displacing deaths by more than months, of greater public health significance is the potential for long-term impacts that may shorten lives by years or that may lead to chronic cardiopulmonary morbidity. Several prospective cohort studies provide evidence of such long-term effects, including associations between ambient particles and lung cancer (3-5). Whereas acute effects may be limited to those individual's with existing cardiopulmonary disease, chronic exposures may affect a much larger proportion of the exposed population. Although the epidemiologic evidence points to a causal relationship with particles originating in combustion processes, the biological mechanism(s) as well as the exact types and sizes of particles involved are the subjects of intensive investigation. One hypothesis is that the ultrafine particle size fraction is responsible for the epidemiologic observations (6). This hypothesis is partly based on the fact that the majority of atmospheric particles, by number, are in the ultrafine mode. These particles, produced in combustion processes, are likely to contain condensates of toxic metals and surface acidity. In animal models, ultrafine particles appear to induce an intense inflammatory reaction and are believed to be translocated to the pulmonary interstitium in large numbers (7,8).

Despite the interest in the topic, little is known of the types, sizes, and locations of ambient atmospheric particles in human lungs. Direct measurements of deposited particles in humans are difficult, but animal models show that virtually all types of inhaled particles can be translocated across the alveolar epithelium to the interstitium, from which location they are cleared slowly or not at all (9). Analysis of lung parenchymal particle burden can thus provide an indication of the types and numbers of particles to which an individual has been exposed. …