THE ASSOCIATION BETWEEN AMBIENT CARBON-MONOXIDE LEVELS AND DAILY MORTALITY IN TORONTO CANADA

The role of ambient levels of carbon monoxide (CO) in the exacerbation of heart problems in individuals with both cardiac and other diseases was examined by comparing daily variations in CO levels and daily flu ctuations in nonaccidental mortality in metropolitan Toronto for the 1 5-year period 1980-1994. After adjusting the mortality time series for day-of-the-week effects, nonparametic smoothed functions of day of st udy and weather variables, statistically significant positive associat ions were observed between daily fluctuations in mortality and ambient levels of carbon monoxide, nitrogen dioxide, sulfur dioxide, coeffici ent of haze, total suspended particulate matter, sulfates, and estimat ed PM,, and PM,,. However, the effects of this complex mixture of air pollutants could be almost completely explained by the levels of CO an d total suspended particulates (TSP). Of the 40 daily nonaccidental de aths in metropolitan Toronto, 4.7% (95% confidence interval of 3.4%-6. 1%) could be attributable to CO while TSP contributed an additional 1. 0% (95% confidence interval of 0.2-1.9%), based on changes in CO and T SP equivalent to their average concentrations. Statistically significa nt positive associations were observed between CO and mortality in all seasons, age, and disease groupings examined. Carbon monoxide should be considered as a potential public health risk to urban populations a t current ambient exposure levels.