Abstract
BackgroundAir pollution in Darwin, Northern Australia, is dominated by smoke from seasonal fires in the surrounding savanna that burn during the dry season from April to November. Our aim was to study the association between particulate matter less than or equal to 10 microns diameter (PM10) and daily emergency hospital admissions for cardio-respiratory diseases for each fire season from 1996 to 2005. We also investigated whether the relationship differed in indigenous Australians; a disadvantaged population sub-group.MethodsDaily PM10 exposure levels were estimated for the population of the city from visibility data using a previously validated model. We used over-dispersed Poisson generalized linear models with parametric smoothing functions for time and meteorology to examine the association between admissions and PM10 up to three days prior. An interaction between indigenous status and PM10 was included to examine differences in the impact on indigenous people.ResultsWe found both positive and negative associations and our estimates had wide confidence intervals. There were generally positive associations between respiratory disease and PM10 but not with cardiovascular disease. An increase of 10 μg/m3 in same-day estimated ambient PM10 was associated with a 4.81% (95%CI: -1.04%, 11.01%) increase in total respiratory admissions. When the interaction between indigenous status and PM10 was assessed a statistically different association was found between PM10 and admissions three days later for respiratory infections of indigenous people (15.02%; 95%CI: 3.73%, 27.54%) than for non-indigenous people (0.67%; 95%CI: -7.55%, 9.61%). There were generally negative estimates for cardiovascular conditions. For non-indigenous admissions the estimated association with total cardiovascular admissions for same day ambient PM10 and admissions was -3.43% (95%CI: -9.00%, 2.49%) and the estimate for indigenous admissions was -3.78% (95%CI: -13.4%, 6.91%), although ambient PM10 did have positive (non-significant) associations with cardiovascular admissions of indigenous people two and three days later.ConclusionWe observed positive associations between vegetation fire smoke and daily hospital admissions for respiratory diseases that were stronger in indigenous people. While this study was limited by the use of estimated rather than measured exposure data, the results are consistent with the currently small evidence base concerning this source of air pollution.
Highlights
Air pollution in Darwin, Northern Australia, is dominated by smoke from seasonal fires in the surrounding savanna that burn during the dry season from April to November
The relative role of particulates derived from biomass as opposed to fossil fuel combustion remains unclear, two empirical studies of PM10 derived from vegetation fires [3,4], and one review of studies examining PM10 from wood smoke [5] all observed that the magnitude of associations with respiratory outcomes is greater when Particulate Matter (PM) was derived from biomass combustion
Studies examining a single source of ambient PM10 are infrequent because of the difficulty finding a site without a mixture of various pollutants, and the complexity of apportioning contributions from different sources [2,6]
Summary
Air pollution in Darwin, Northern Australia, is dominated by smoke from seasonal fires in the surrounding savanna that burn during the dry season from April to November. Our aim was to study the association between particulate matter less than or equal to 10 microns diameter (PM10) and daily emergency hospital admissions for cardio-respiratory diseases for each fire season from 1996 to 2005. Associations between daily hospital admissions for cardio-respiratory diseases and particulate matter less than or equal to 10 microns in aerodynamic diameter (PM10) have been described in many settings worldwide including North America, Europe, Asia and Australia [1]. The relative role of particulates derived from biomass as opposed to fossil fuel combustion remains unclear, two empirical studies of PM10 derived from vegetation fires [3,4], and one review of studies examining PM10 from wood smoke [5] all observed that the magnitude of associations with respiratory outcomes is greater when PM was derived from biomass combustion. A few epidemiological studies have apportioned total PM according to a range of sources (such as biomass, crustal and motor vehicles) and have found a range of different clinical outcomes were associated with different exposure sources [7,8]
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