Re: Deaths from fossil fuel burning air pollution

[Bernard L Cohen <blc+@pitt.edu>]

On Mon, 20 Nov 2000, Otto G. Raabe wrote:

> At 09:25 AM 11/20/00 -0600, Prof. Cohen wrote:
> >
> >A substantial amount of science has gone into
> >settling on fine particulate as the best indicator of air pollution health
> >effects. Most other pollutants correlate closely with it, so it serves as
> >a surrogate.
  
> I agree with Prof. Cohen's statement above. However, my point is that it is
> not the particulate matter, per se, that is responsible for the observed
> effects. The last EPA criteria document on particulate matter shows that it
> takes really high concentrations of low-toxicity particulate matter to
> yield any significant effects on laboratory animal studies involving
> chronic exposures. However, the EPA and the particulate matter
> epidemiologist apparently believe that the particulate matter by itself,
> especially of submicronic particles, is responsible for increased mortality
> and morbidity even at low concentrations and for acute exposures with a
> linear no-threshold (LNT) dose-response.

	--I don't know the EPA viewpoint, but for the many members of the
air pollution health effects community that I know, there is a recognition
that fine particulate is a surrogate for all types of air pollution, all
of which are correlated.
	Incidently, there is no "linear-no threshold" assumption stated,
or even implied. There are lots of data on exposure vs health effects, and
these are analyzed with regression analysis involving other potential
confounding factors, i.e. multiple regression. Regression analysis by
definition gives a linear fit to the data, but it is not "linear-no
threshold"; the (0,0) point is not included in the regression analysis.
	The reason why "linear-no threshold" has a bad name is because it
is used to extrapolate data at very high exposures down into the low
exposure region where there are no data. In the case of air pollution,
only the region where there are data are considered. The very high
exposure data are not considered, and the zero exposure case where there
are no data is not considered. Even rural areas where exposures are very
low are not considered because there would be many potential confounding
factors that would be very different from urban areas.

Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


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