Association between particulate- and gas-phase components of urban air pollution and daily mortality in eight Canadian cities

Although some consensus has emerged among the scientific and regulatory com munities that the urban ambient atmospheric mix of combustion related pollu tants is a determinant of population health, the relative toxicity of the c hemical and physical components of this complex mixture remains unclear. Da ily mortality rates and concurrent data on size-fractionated particulate ma ss and gaseous pollutants were obtained in eight of Canada's largest cities from 1986 to 1996 inclusive in order to examine the relative toxicity of t he components of the mixture of ambient air pollutants to which Canadians a re exposed. Positive and statistically significant associations were observ ed between daily variations in both gas- and particulate-phase pollution an d daily fluctuations in mortality rates. The association between air pollut ion and mortality could not be explained by temporal variation in either mo rtality rates or weather factors. Fine particulate mass (less than 2.5 mum in average aerometric diameter) was a stronger predictor of mortality than coarse mass (between 2.5 and 10 mum). Size-fractionated particulate mass ex plained 28% of the total health effect of the mixture, with the remaining e ffects accounted for by the gases. Forty-seven elemental concentrations wer e obtained for the fine and coarse fraction using nondestructive x-ray fluo rescence techniques. Sulfate concentrations were obtained by ion chromatogr aphy. Sulfate ion, iron, nickel, and zinc from the fine fraction were most strongly associated with mortality The total effect of these four component s was greater than that for fine mass alone, suggesting that the characteri stics of the complex chemical mixture in the fine fraction may be a better predictor of mortality than mass alone. However, the variation in the effec ts of the constituents of the fine fraction between cities was greater than the variation in the mass effect, implying that there are additional toxic components of fine particulate matter not examined in this study whose con centrations and effects vary between locations. One of these components, ca rbon, represents half the mass of fine particulate matter. We recommend tha t measurements of elemental and organic carbon be undertaken in Canadian ur ban environments to examine their potential effects on human health.