[sustran] More evidence on particulate air pollution danger

[SUSTRAN Resource Centre]

New Scientist this week reports:

Hold your breath
Tiny particles of dirt in the air of cities really can kill you 

A FRESH analysis of a classic pollution study has vindicated its conclusion
that city-dwellers in Europe and the US are dying young because of
microscopic particles in the air. 

Most of the concern about particulate pollution began in 1993 with the
publication of the Harvard "Six Cities" study, which identified particles
with a diameter of less than 10 micrometres (PM10) as a threat to public
health. A team of researchers at the Harvard School of Public Health in
Boston, led by Douglas Dockery, compared death rates and pollution levels
in six American cities by following more than 8000 adults for up to 16 years. 

They found that the death rates increased in almost direct proportion to
the level of particulate pollution. People living in the most polluted
city--Steubenville, Ohio--had a 26 per cent risk of dying young compared
with residents of the cleanest city, which was Portage, Wisconsin (New
England Journal of Medicine, vol 329, p 1753). 

A larger study by the American Cancer Society in 1995 tested these findings
by following 550 000 adults over seven years. Once again, there appeared to
be a strong link between death rates and particulate pollution. Critics of
these studies argued, however, that other differences between the
cities--such as poverty--might be responsible for the different death rates. 

So the Health Effects Institute, an independent research organisation in
Cambridge, Massachusetts, funded jointly by industry and the US
government's Environmental Protection Agency, spent three years
re-analysing the data and testing dozens of different explanations for the
results. They controlled for factors such as education, ethnicity, income
levels and the availability of health care, as well as differences in other
pollutants, temperature and humidity. 

But the re-analysis broadly confirmed the original conclusion. "For the
most part, the inclusion of these additional [factors] did not alter the
association," says team leader Daniel Krewski of the University of Ottawa.
"We were very surprised and relieved, actually," says Dockery. Adrian Pope
of the Brigham Young University in Provo, Utah, who led the American Cancer
Society study, hopes the results will end the controversy. 

The HEI study suggests that tiny particles with a diameter of less than 2.5
micrometres, or PM2.5, are more dangerous than PM10. Most of the PM2.5
fraction is caused by by-products of combustion, which may contain more
carcinogens. 

Currently the US sets air-quality standards for both PM10 and PM2.5. Europe
only has a standard for PM10, but the European Commission is due to review
its particle pollution standards. Roy Harrison of the University of
Birmingham, who advises the British government on particulate air
pollution, says separate monitoring is unnecessary because, in Britain at
least, PM2.5 levels rise and fall with PM10 levels. 

But Tim Brown of Britain's National Society for Clean Air says researchers
need to know more about how particle composition--and not just
size--affects health. Brown asks: "Are all particles equally dangerous?"

Nell Boyce 

>From New Scientist magazine, 05 August 2000.

© Copyright New Scientist, RBI Limited 2000
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Distributed for the purpose of education and research.

A. Rahman Paul BARTER
SUSTRAN Resource Centre
Information services for the Sustainable Transport Action Network
for Asia and the Pacific (the SUSTRAN Network)
sustran at po.jaring.my 
http://www.malaysiakini.com/sustran
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