A COMPARISON OF HEALTH EFFECTS FROM EXPOSURE TO AMBIENT AND NON-AMBIENT PARTICLES

Abstract

ISEE-89 Introduction: The plausibility of epidemiological associations between adverse health effects and outdoor concentrations of airborne particulate matter (PM) has been questioned by studies demonstrating low correlations between individual exposures to ambient PM and ambient PM concentrations. Since personal exposure to PM is frequently dominated by exposure to non-ambient particles, it is important to evaluate the potential health impacts of both ambient and non-ambient exposures. Methods: In summer 1998, personal exposures to PM2.5 and sulfate, and ambient concentrations of PM10, PM2.5 and sulfate were measured for a repeated measures (7 repeats) panel study of respiratory and cardiovascular effects in chronic obstructive pulmonary disease (COPD) patients (n=16). In a further analysis of this dataset, we used an estimation method, based on time-activity data and the personal/ambient ratio of sulfate as a marker for the infiltration of ambient particles with the same size distribution, to develop separate estimates of exposures to ambient PM2.5, PM10 and PM10-2.5 and to non-ambient PM2.5. Health outcome measures included lung function, blood pressure, heart rate variability, and arrhythmia. The concentrations and association with health effects of these estimated exposures were compared to the originally measured total personal exposures and to measured ambient concentrations. Use of mixed models and elimination of one day of exposure associated with transported Asian dust led to larger and more significant associations than found in an earlier analysis. Results: Personal exposures to PM2.5 were dominated by exposures to non-ambient PM2.5 (56% on average), which were uncorrelated with exposures to ambient PM2.5 and to measured ambient PM2.5. For most outcomes, ambient exposure provided greater and more significant effect estimates in the expected direction than non-ambient or total exposure. For most outcomes, the effect estimates between PM indicators and health outcomes were similar in direction and magnitude for ambient concentrations and their respective ambient exposures. However, for most outcomes, effect estimates for ambient exposures were larger and more significant than those for ambient concentrations. Discussion: This study demonstrates a methodology that permits epidemiological analyses using separate indicators for ambient and non-ambient exposure. The results support the hypotheses that ambient exposures provide more precise and stronger estimates of effect in epidemiological analyses than ambient concentrations and that ambient exposures and non-ambient exposures will demonstrate different associations with health outcomes. These results also support the plausibility of associations between ambient concentrations and adverse health outcomes.