The researchers found that both pollutants had similar effects -- mainly raising the rate of cardiopulmonary (defined) deaths. This is not surprising, since they both usually originate in burning fossil fuels, and are usually found in combination.
But the large study had enough statistical power (defined) to show subtle distinctions among the pollutants' effects. While sulfates were linked with increased rates of lung cancer, particulates were linked with an increase in all deaths. (Incidentally, cigarette smoking was linked with all three causes of death.You can choose not to smoke, but breathing's kind of ... mandatory. (Care to light up a Why File on nicotine addiction?)
The reason for the term "cardiopulmonary disease," says study co-author Dockery, is that it's often hard to distinguish the cause of death. "Especially in the elderly, the differentiation between cardiovascular disease and respiratory disease as a cause of death is very poor." Many of the victims arrive dead at the hospital, and the cause of death may be listed as heart attack with no mention on the death certificate of any contribution from lung disease or air pollution.
What exactly is the mechanism -- or mechanisms -- through which air pollutants harm the body? Although there's plenty of room for speculation, Dockery notes that vulnerable people don't die immediately when the pollution rises, rather, death rates tend to rise for a few days during pollution episodes. This, he says, implicates a "cascade of effects" in the deaths.
