http://www.doh.gov.uk/comeap/
Committee On The Medical Effects Of Air Pollutants (COMEAP)
Thursday, May 03, 2001
COMEAP is an Advisory Committee of independent experts that provides
advice to Government Departments and Agencies on all matters
concerning the potential toxicity and effects upon health of air
pollutants.
Most members are appointed as independent scientific and medical
experts on the basis of their special skills and knowledge. The one
exception to this is the public interest member of the Committee who
is appointed for knowledge of consumer, and other, matters. At all
times individuals are required to declare conflicts of interest and
during discussions they may be disqualified at the Chairman's
discretion from contributing to the conclusions and recommendations of
the Committee.
The independent members are supported in their work by a secretariat
provided by the Department of Health. The secretariat have scientific
expertise that enables them to provide members with comprehensive
background information and briefing papers that inform the
decision-making processes of the Committee.
http://www.doh.gov.uk/comeap/longtermeffects.pdf
...
Our conclusions are as follows:
(i) We consider it more likely than not that a causal association
exists between long term exposure to particles and mortality. We
consider that this association is transferable to the UK, although the
quantitative impact may not be exactly the same.
(ii) We consider that, given there is information regarding the size
of the effect, it is preferable to assess this and comment on it
rather than ignore it. Nonetheless there are great uncertainties in
this process and it is vital that these are made clear. We consider
that the long-term effects are more uncertain than the short-term
effects but that it would be unwise to dismiss them completely.
(iii) It is possible, although unlikely, that there are no long term
effects, if the results are explained by unknown confounders,
confounding by sulphur dioxide or lack of control for spatial
variation. If so, the only effect on mortality would be that detected
in the time-series studies.
(iv) An approximate calculation assuming a loss of 2 to 6 months of
life per death brought forward suggests a gain of 0.007 to 0.02
million life years per µg/m 3 drop in PM10 for mortality from
short-term exposure as detected in time-series studies. Although
intended only as a rough comparison, this does suggest that the gain
in life years from the cohort studies is at least 10 fold greater than
estimates from the time series studies alone.
(v) The above calculation and those below are based on the population
of England and Wales alive in 2000 followed for 105 years as an
illustration. Other populations and years of follow-up could be used
provided the same methodology is followed. The calculations below are
expressed per µg/m 3 drop in PM2.5 representing around a 5 % reduction
from current levels.
(vi) Using a range of possible coefficients from the cohort studies
leads to an estimate of 0.2 to 4.1 million life years gained per µg/m
3 drop in PM2.5. This could be expressed as up to 1 month per person
on average if everyone was affected but could also represent a larger
gain for fewer people.
(vii) We consider that estimates at the lower end of the range are
more likely. We know that a few of the confounders in the HEI
reanalysis reduced the relative risks and there may be other unknown
confounders. If higher exposures in the past are contributing to the
effect, then the predicted effect of current levels will be
overestimated. We consider the upper end of the range to be
implausibly large compared with risks in other contexts and with the
total changes in life expectancy seen in the last 20 to 30 years when
particle levels have been dropping dramatically.
(viii) The majority of the Committee considered that an estimate of
0.2 – 0.5 million life years (1.5 to 3.5 days per person or more)
could be used to estimate the benefits of pollution reduction. The
higher estimates could be included in sensitivity analysis in
increasing bands of uncertainty as the size of the estimate increases.
The possibility of there being no long term effects should also be
included in sensitivity analysis.
(ix) For a birth cohort born in 2000 and followed up for their
lifetime, the gain in life expectancy for the same reduction is
estimated as between 0.5 and 4.5 weeks.
(x) Taking actual exposures into account, the estimates are less than
those for active smoking but the relative risk for mortality from
heart disease is similar to that for passive smoking. The estimates
are in line with others for air pollution in the literature.
(xi) The key uncertainties are whether the results can be explained by
undetected confounding, whether high exposures in the past lead to an
overestimation of the effect, what lagtimes and what duration of
exposure are required for the effect and a lack of understanding of
the underlying mechanism. These uncertainties need to be addressed by
further research.
= - = - = - = - = - = - = - = - = - = - = - =
(i) Our comments on the key uncertainties (see below) should be
quoted.
(ii) Application of the results to large changes in pollution adds to
the uncertainties (see paragraph 38).
(iii) The composition of the particles is important; it cannot be
assumed that these results extend to pollution climates very different
from those typical of US cities. For example, we do not know whether
these estimates would apply around point sources.
(iv) These results relate not only to a 1µg/m 3 change in PM2.5 but
also to a particular population (those alive in 2000) and a particular
length of follow-up (105 years). We acknowledge that cost-benefit
analysis of particular policy scenarios may need different populations
and follow-up periods. We consider that this could be dealt with by
performing new lifetable calculations, provided the same methodology
was used.
--
Gary N. Greenberg, MD MPH Sysop / Moderator Occ-Env-Med-L MailList
[log in to unmask] Duke Occupat, Environ, Int & Fam Medicine
OEM-L Maillist Website: http://occhealthnews.net
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