Do socioeconomic characteristics modify the short term association between air pollution and mortality? Evidence from a zonal time series in Hamilton, Canada.
OBJECTIVE
To assess the short term association between air pollution and mortality in different zones of an industrial city. An intra-urban study design is used to test the hypothesis that socioeconomic characteristics modify the acute health effects of ambient air pollution exposure.


METHODS
The City of Hamilton, Canada, was divided into five zones based on proximity to fixed site air pollution monitors. Within each zone, daily counts of non-trauma mortality and air pollution estimates were combined. Generalised linear models (GLMs) were used to test mortality associations with sulphur dioxide (SO(2)) and with particulate air pollution measured by the coefficient of haze (CoH).


RESULTS
Increased mortality was associated with air pollution exposure in a citywide model and in intra-urban zones with lower socioeconomic characteristics. Low educational attainment and high manufacturing employment in the zones significantly and positively modified the acute mortality effects of air pollution exposure.


CONCLUSIONS
Three possible explanations are proposed for the observed effect modification by education and manufacturing: (1) those in manufacturing receive higher workplace exposures that combine with ambient exposures to produce larger health effects; (2) persons with lower education are less mobile and experience less exposure measurement error, which reduces bias toward the null; or (3) manufacturing and education proxy for many social variables representing material deprivation, and poor material conditions increase susceptibility to health risks from air pollution.
Jerrett
M
M
School of Geography and Geology and McMaster Institute of Environment and Health, McMaster University, Hamilton, Ontario, Canada. jerrettm@mcmaster.ca
Burnett
R T
RT
Brook
J
J
Kanaroglou
P
P
Giovis
C
C
Finkelstein
N
N
Hutchison
B
B
D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000633:toxicity; D000397:Air Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data; D004522:Educational Status; D015987:Effect Modifier, Epidemiologic; D005260:Female; D006801:Humans; D007221:Industry; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009026:Mortality; D009864:Ontario / Q000453:epidemiology; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012959:Socioeconomic Factors; D014504:Urban Health
D000393:Air Pollutants