Health effects of sulfur-related environmental air pollution. I. Executive summary.

The motivation of simulating real-world environmental exposure in a number of long-term studies with dogs was to address the question of whether or not perpetual inhalation of air pollutants can initiate diseases in healthy lungs and can thus contribute to the increasing prevalence of respiratory diseases in industrialized countries. The major conclusion of this article is that this question has to be answered in the negative for the simultaneous inhalation of the major constituents of combustion-related air pollution, particle-associated sulfur(IV), and particle-associated hydrogen ions. Over 13 mo, 8 healthy beagle dogs were exposed in 2 whole-body chambers daily for 16.5 h to 1 microm neutral sulfite [sulfur(IV)] particles at a mass concentration of 1.5 mg m-3 and for 6 h to 1.1 microm acidic sulfate particles carrying 15 micromol m-3 hydrogen ions into the canine lungs. This longitudinal study was characterized by repeated observations of individual respiratory response patterns. To establish baseline data the dogs were repeatedly examined preexposure while the chambers were ventilated over 16 mo with clean air. Each individual served thus as its own control. Another eight dogs served as additional controls. They were housed in 2 chambers ventilated with clean air over the entire study period of 29 mo. To assess response patterns, respiratory lung function tests were performed pre- and postexposure, segmental lung lavages were repeatedly performed to obtain epithelial lining fluid from the lungs for analysis of cell content, cell function, and biochemical indicators of lung injury, and radiolabeled test particles were used to study pathways of intrapulmonary particle elimination. At the end of the study, the lungs of all animals were morphologically and morphometrically examined. Functional and structural responses were finally compared to those observed previously as a result of a sole exposure of canine lungs to neutral sulfite particles over 10 mo (Heyder et al., 1992). Interactions between responses induced by neutral sulfite and acidic sulfate particles occurred, but antagonism rather than synergism was observed. The responses induced by sulfur(IV) were less pronounced, not detectable, or even reversed when hydrogen ions were also delivered to the lungs. On the other hand, responses not induced by the sole exposure to sulfur(IV) were observed: The activity of alkaline phosphatase was elevated and type II pneumocytes proliferated. It can, however, be concluded that long-term exposure of healthy lungs to particle-associated neutral sulfur(IV) and hydrogen ions at concentration close to ambient levels causes subtle respiratory responses but does not initiate pathological processes in the lungs. In other words, the perpetual inhalation of sulfur(IV) and hydrogen ions from the atmospheric environment presents no health risk to the healthy lungs. It is thus also very unlikely that respiratory diseases can be initiated by the inhalation of these pollutants.