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Epi Wit & Wisdom Articles
Air Pollution Described as
Hottest Topic in Environmental Epidemiology Today
Huge Change in Thinking Brought
About by Epidemiologic Studies
Work Called a “Success for
Epidemiology”
Speaking during the opening
session of the ISEE meeting in Athens, Swedish epidemiologist Goran
Pershagen described air pollution as “the hottest topic in
environmental epidemiology today.” Intrigued by this statement and
wondering what he meant by it, the Epi Monitor asked investigators at
the meeting to expand on Dr. Pershagen’s statement. What we learned is
that important developments have been happening in the area of air
pollution.
The first point to understand is
that thinking about air pollution and health effects has been turned
upside down over the last decade. Under the old mindset, the thinking
was that air pollution is under control because the particle content
in the air has been reduced very dramatically and there is visible
improvement in the air quality.
However, pioneering time series
studies done in the 1990’s by investigators at the Harvard School of
Public Health led by Douglas Dockery and Joel Schwartz have found
otherwise. According to Dockery, “the really big change has been the
discovery that threshold levels for health effects exist for
individuals, but not for populations. As concentration of air
pollutants goes up, you knock off those at the lower thresholds. What
we’re facing is epidemiology showing us an effect at lower and lower
levels. In the old mode of thinking, we had a “bright line” but now we
should not think that way.”
Robert Maynard, head of air
pollution policy development in the UK Department of Health agrees.
According to Maynard, “there has been a complete change in views over
the last thirty years in the UK from thinking that thresholds exist to
thinking today that there are no thresholds. Thus, air pollution
cannot be defeated like smallpox. Because there are still effects at
the lowest exposure levels, the goal must be to control air pollution
to the extent we can afford it,” said Maynard.
Aaron Cohen from the Health
Effects Institute makes another interesting point. “Air pollution
epidemiology has shown that small effects can be studied and that
those associations are real. This work challenges the idea about the
limits to epidemiology,” he said.
The second point to understand
about why air pollution is a hot topic in environmental epidemiology
is that following these pioneering observations there has been a wave
of papers, largely confirmatory, and carried out in different
climates, according to Maynard. Klea Katsouyanni, Greek leader of the
European time series studies on air pollution, calls the work on air
pollution “a success for epidemiology,” and notes that “there is a
pressure to be active in this area.”
To understand just how hot this
topic is, Dockery told the Epi Monitor that the United States
Environmental Protection Agency is putting millions in particle
research, and that a real bolus of money for air pollution has been
added over the last two years.
Other factors contributing to
the increased level of activity in air pollution are a huge expansion
in air pollution monitoring and a surge in mechanistic research. The
reason for the former is obvious. The interest in the latter is
fueled, in part, by concerns of scientists outside of epidemiology who
are upset about the heavy reliance on epidemiology to support the new
thinking and the new regulatory approaches. These scientists are
reportedly very vocal in stating that we do not yet understand the
mechanisms underlying the epidemiologic observations, and, with very
small risks being reported, are calling for more mechanistic
information.
To further understand why air
pollution is hot, one has only to reflect on the observations made by
Maynard during his opening keynote address to the participants. He
informed epidemiologists that environmental epidemiology has taken on
political importance and consequently now has power because
governments are forced to listen and “politicians can be scared
witless” by what environmental epidemiologists have to say. He
cautioned the audience that responsibility always goes with power and
he urged participants to exercise it responsibly.
To illustrate his points,
Maynard invited the audience to assume that there are 20,000 deaths
per year in the UK that are advanced (i.e. occur earlier than they
otherwise might without exposure to air pollution). What the
politician or policy maker needs to know according to Maynard is—by
how much are these deaths advanced? What condition are the people in
who die early? How much would these people be willing to pay to avoid
dying? What do the results mean for the population? how does this
problem compare to other problems in public health? What is an
acceptable risk?
Evidence for the controversies
in air pollution control stirred up by the epidemiologic work on air
pollution can be found in the recent US court decision which threw out
air quality standards for fine soot developed by EPA. According to a
report in the New York Times in mid-May, the court ruling said “What
EPA lacks is any determinate criterion for drawing lines...It has
failed to state intelligibly how much is too much.” The Times went on
to report “The decision points out what people on both sides of the
case say is a growing contradiction in air pollution policy. Congress
told the EPA to set standards that protect the public’s health with
‘an adequate margin of safety’, on the theory that there is a
threshold below which any pollutant is safe. But some scientific
studies now say that for contaminants like ground-level ozone, known
as smog, any exposure may be harmful.”
What has been called a success
for epidemiology in finding a real threat to health has now become a
huge challenge to society to translate into effective and acceptable
control measures. This hot topic is unlikely to cool anytime soon. In
fact, the pace in air pollution control seems to be incredibly slow.
The Harvard studies were done in 89 - 90, reported in 1992, and the
EPA standards were released in 1997. The states have until 2012 to
reach compliance with the standards. Stay tuned....
Published October 1999 v
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