Ambient PM(2.5) and risk of emergency room visits for myocardial infarction: impact of regional PM(2.5) oxidative potential: a case-crossover study

BACKGROUND: Regional differences in the oxidative potential of fine particulate air pollution (PM(2.5)) may modify its impact on the risk of myocardial infarction. METHODS: A case-crossover study was conducted in 16 cities in Ontario, Canada to evaluate the impact of regional PM(2.5) oxidative potential on the relationship between PM(2.5) and emergency room visits for myocardial infarction. Daily air pollution and meteorological data were collected between 2004 and 2011 from provincial monitoring sites and regional estimates of glutathione (OP(GSH)) and ascorbate-related (OP(AA)) oxidative potential were determined using an acellular assay based on a synthetic respiratory tract lining fluid. Exposure variables for the combined oxidant capacity of NO(2) and O(3) were also examined using their sum (O(x)) and a weighted average (O(x)(wt)) based on their redox potentials. RESULTS: In total, 30,101 cases of myocardial infarction were included in the analysis. For regions above the 90(th) percentile of OP(GSH) each 5 μg/m(3) increase in same-day PM(2.5) was associated with a 7.9 % (95 % CI: 4.1, 12) increased risk of myocardial infarction whereas a 4.1 % (95 % CI: 0.26, 8.0) increase was observed in regions above the 75(th) percentile and no association was observed below the 50(th) percentile (p-interaction = 0.026). A significant 3-way interaction was detected with the strongest associations between PM(2.5) and myocardial infarction occurring in areas with high regional OP(GSH) and high O(x)(wt) (p-interaction < 0.001). CONCLUSIONS: Regional PM(2.5) oxidative potential may modify the impact of PM(2.5) on the risk of myocardial infarction. The combined oxidant capacity of NO(2) and O(3) may magnify this effect. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12940-016-0129-9) contains supplementary material, which is available to authorized users.