Despite everything you've read to this point, epidemiologist Suresh Moolgavkar of the University of Washington argues that the EPA proposal is "premature. ... Pollution is a very complex mixture, and there's simply not enough information to single out any one component and say that's responsible for the health effects."
But Dockery notes that even though pollutants always occur in combination, statistical analysis can decipher the specific health effects of individual pollutants. "When we see particles and sulfur dioxide, or particles and ozone, or particles and carbon monoxide, the excess deaths are still linked to the particles," he says. "We don't fully understand the multiple pollutants issue, but I've not seen anything yet that says particles are not responsible" for the extra deaths and disease.
Furthermore, Moolgavkar acknowledges that the approach he suggests would require what scientists like best: more study and more funding. "I think it would be possible to gather the data -- an attempt could be made in the next 5 to 10 years -- to try to tease out exactly what is going on. To spend a few million dollars a year on research -- that's not much given the costs" of control.
Not just in the United States...
The EPA is not the only organization showing growing concern about particulate pollution. The World Health Organization (WHO), which is in the process of setting new, tighter standards, calculates that raising ambient levels by 50 micrograms per cubic meter causes a doubling of deaths and symptoms of common respiratory disorders, such as asthma and emphysema (see "WHO Sets New Guidelines for Air Pollution" in the bibliography).
The WHO standards will be used as a basis for setting standards in Europe, where the mean urban level of particulates is about 20 micrograms per cubic meter. As usual, certain cities, including Pisa, Athens, Belfast, have much higher levels.
One of the most disturbing results from the particulate studies is the seeming absence of a safe level. In other words, any particles are too many particles, in terms of keeping the most vulnerable people healthy. In epidemiological terms, this is called a "no-threshold" dose-response curve, and it poses an insoluble problem: how clean is clean enough?
There's another problem: Regulators are stuck with a system designed for pollutants that do have safe thresholds, Pope says. "If you are going to use a threshold model to set a standard for a pollutant that doesn't fit the model, you are going to run into problems." Instead of forcing reality to fit the model, Pope suggests that society must choose an acceptable level of risk and regulate to that objective. He acknowledges that although this may sound difficult, it's done all the time on questions of auto and air safety.
The Why Files covered the threshold issue in a File on the health effects of ionizing radiation. Care to surf on by?
The argument against waiting for better data before regulating is two-fold. Lives are on the line today, say those who have studied the issue. And even if the regulation is passed, 5 to 10 years will elapse before it improves air quality.
What are the benefits?
How many people would be helped by the regulation? Hard to say, unfortunately. The Natural Resources Defense Council says, "Every year, some 64,000 people may die prematurely from cardiopulmonary causes linked to particulate air pollution. ... NRDC's analysis shows that between 4,662 and 37,562 lives could be prolonged" by the regulation.
But Pope is not convinced by those numbers, saying the benefits can be seen in various ways. On one hand, he says, we could focus on the small increases in death rates, mainly among vulnerable people -- children, asthmatics and the elderly -- in the time series studies. From that standpoint, the benefits of the EPA regulations would be rather limited.
On the other hard, he says, it's clear that "long-term exposure to combustion-source particulates increases your risk of respiratory disease and early death." Under this analysis, he says, "basically everybody" stands to benefit from the new EPA regulations.
So it's solved, then? Just cut the rates, and breathe easier?
