2.2.2 Adverse effects of coarse particles
WHO
states:
"Answer:
There are a large number
of epidemiological studies showing that
PM10 (which includes both fine
andcoarse
particles) has adverse health effects.
Although smaller in number, the existing
studies on the fine particle fraction
(PM2.5)
show that there are also health effects
from this fraction. Only recently have
investigators begun to separately address
health effects of coarse particles (PM10-2.5).
There is limited evidence that coarse
particles are associated independently
of PM2.5
with mortality in time series studies.
One study has investigated the effect
of long-term exposure to coarse particles
on life
expectancy without producing evidence
of altered survival. There is evidence
that coarse particles are independently
associated with morbidity
endpoints
such as respiratory hospitalizations in
time series studies. Considerations of
particle dosimetry, chemistry and toxicology
provide further evidence of adverse health
effects of coarse PM. Therefore, there
is sufficient concern about the health
effects of coarse particles to justify
their control.
Rationale: Composition
The difference in size
and chemical composition between the coarse
and the fine fraction of PM is likely
to result in differences in type of disease
and severity of effect. On the other hand,
particle formation can be a complex and
dynamic process that depends upon atmospheric
chemistry and agglomerative interactions
between the different-sized particles
present in the particle phase. Particle
agglomerates that are large enough to
be in the coarse fraction may contain
many ultrafine
particles and other constituents attached
to them that originally arose in the ultrafine
fraction. Results of one of the few published
studies, in which coarse and fine PM where
compared for their effects showed that
on the equal mass basis, coarse and fine
particles both produce pulmonary inflammation
(Dick et al., 2003; Shi et al, 2003; Pozzi
et al., 2003).
Toxicology
Whereas the epidemiological studies associate
PM10 or PM2.5
with health effects a rapidly increasing
number of toxicological
studies focus on the different size fractions
within PM10. Most of these
studies apply either concentrators for
inhalation studies or novel PM sampling
techniques for in vitro or in vivo health
effects studies.
Becker et al. (2002, 2003)
studied the potency to induce inflammatory
mediators of coarse, fine and ultrafine
ambient
PM. They observed the strongest effects
in the coarse fraction, and found an absence
of effect from ultrafine particles. The
authors suggest that the effects are linked
with the presence of microbial cell structures
and endotoxins. In support of this, Schins
et al. (in press) have investigated the
inflammogenic potential of coarse (2.5–10µm)
and fine (<2.5µm)
PM from both a rural and an industrial
location in Germany. Bronchoalveolar lavage
(BAL) of rat lungs 18 hours after instillation
with PM showed that, irrespective of the
sampling location, the coarse fraction
of PM10 caused neutrophilic
inflammation
in rat lungs, while its fine counterpart
did not. The rural sample of coarse PM
also caused a significant increase in
the TNF content as well as glutathione
depletion in the BAL fluid. Endotoxin
present of the coarse fraction was the
most likely explanation of this effect.
Since broncho-constriction
is a clear symptom in people with chronic
obstructive pulmonary disease or asthma,
and dosimetry models predict that the
tracheobronchial airways are also target
for PM deposition of particles >1 µm,
a relationship might be present between
coarse mode PM and bronchoconstriction.
Dailey et al. (2002) also studied the
effects of the three size fractions in
airway epithelial cells. Interestingly,
coarse and ultrafine mode PM induced stronger
responses
(cytokine production) then the fine mode,
and again with the coarse mode PM was
the most potent fraction. Li et al. (2002)
described that coarse and fine mode particles
collected in Downey, CA, produced different
effects in an oxidative stress model.
In addition, the effects of coarse mode
particles were most effective when collected
in the fall and winter. Both coarse and
fine PM are able to generate OH radicals
and to induce formation of 8-hydroxy-2’-
deoxyguanosine in cultures of epithelial
cells (Shi et al., 2003). Pozzi et al.
(2003) showed in an in vitro assay that
coarse and fine fraction PM were equally
effective in causing releases of inflammatory
mediators, and that these effects were
much stronger compared with carbon black
suggesting that the contaminants adsorbed
on the particles may be responsible for
the observed induction. Other studies
focus on oxidative stress and the effects
on red blood cells. These have shown that
although haemolytic potential was greater
for the fine
particles than for the coarse
particles in equal mass concentration,
when data were expressed in terms of PM
surface per volume unit of suspension,
the two fractions did not show any significant
hemolytic differences. (Diociaiuti et
al., 2001).
Dosimetry
A substantial fraction of inhaled coarse
particles is deposited in the airways
or lungs. This fraction is substantially
greater than for particles in the fine
fraction (i.e. 0.1< dae <2.5 µm,
see Fig. 4). The difference in tracheobronchial
and thoracic deposition fractions between
children and adults increases with particle
size and is significantly greater for
children (ages of 0–15 years old)
than for adults.
Few investigators have
specifically addressed the particle lung
doses from fine and coarse PM. Venkataraman
& Kao (1999) showed that on a mass
basis, the proportion of fine PM being
deposited in the pulmonary region is three
times larger than the proportion of coarse
PM. The number dose to the pulmonary region,
however, was five orders of magnitude
higher for fine than for coarse PM. This
indicates that if effects of PM would
even [be] partly related to particle number,
the fine fraction completely dominates
effects related to pulmonary deposition.
Fig.
4. Modelled deposition of particles in
the human respiratory
tract
using the MPPD (Price et al., 2002) model
Settings:
Default settings with nose-mouth breathing
pattern.
Epidemiology
In the last 15 years, airborne particles
have been characterized in many epidemiologic
studies by mass concentrations of particles
smaller than 10 micrometer in diameter
(PM10), because particles of
this size can penetrate into the thoracic
part of the airways where they may have
adverse effects. The more inclusive measure
of “Total Suspended Particulates”
(TSP) did incorporate larger particles,
but was considered to be too unspecific
to be used as a basis for air quality
standards aimed at protecting human health.
Because PM10
often to a large extent consists of particles
smaller than a few micrometers, it cannot
be easily distinguished in studies from
fine particulate
matter, often measured as particles
smaller than 2.5 micrometers or PM2.5.
That is not to say that the concentrations
are the same; the issue is that temporal
and spatial variation of PM2.5
and PM10 are often similar,
despite the difference in sources and
composition between fine and coarse particles,
simply because PM2.5
is often a large fraction of PM10.
Only in recent years has
the difference between coarse and fine
particles come to be more explicitly
appreciated in epidemiologic studies.
Investigators have included separate measurements
of fine and coarse particles in their
studies rather than measurements of PM2.5
and PM10. This has shown that,
in contrast to the high correlation between
PM10 andPM2.5,
there is often much less correlation between
PM2.5
and coarse particles, usually defined
and measured as particles larger than
2.5 and smaller than 10 micrometer. Of
note is that sometimes this quantity is
arrived at by subtracting a direct measurement
of PM2.5
from a direct measurement of PM10;
the disadvantage of this is that “coarse”
particle measurement is then affected
by two measurement errors rather than
one. Other sampling configurations separate
fine and coarse particles before they
are collected on filters to be weighed,
or detected by other means. These recent
studies have made it possible to investigate
the role of fine and coarse particles
without running into the complication
that any statement about PM10
is likely to be also valid for (or even
dominated by) PM2.5, simply
because PM2.5
is such a large fraction of PM10.
The observation that the correlation between
“fine” and “coarse”
particles is often low has made it relatively
easy to separate their effects in field
studies.
A detailed description
of occurrence, measurement and correlations
of coarse and fine particles can be found
in Wilson & Suh (1997). These authors
concluded that “fine and coarse
particles are separate classes of pollutants
and should be measured separately in research
and epidemiologic studies. PM2.5
and PM(10–2.5) are indicators or
surrogates, but not measurements, of fine
particles.” To illustrate the last
point, it has been shown that in certain
areas windblown dust significantly contributes
to PM2.5
(Claiborn et al., 2000).
An early example of a
study that addressed fine and coarse PM
separately is a study from the United
States of America (Schwartz et al., 1996)
that found that daily mortality in six
cities was associated with fine particles
but not with coarse
particles. Since then, a body of evidence
has emerged that allows further analysis
of the relative importance of fine and
coarse particles. As there are virtually
no studies that have defined “coarse
particles” other than PM10–2.5
(occasionally PM15–2.5),
what we know about “coarse mass”
or CM refers to particles smaller than
10 (or 15) µm,
and larger than 2.5 µm.
The emphasis is on comparing effect estimates
for fine and coarse particles within studies.
First we try to answer the question whether
there is evidence in recent time series
studies of an effect of coarse particles
on mortality, independent of effects of
fine
particles. These studies are ordered
by number of observations because the
larger the number of observations, the
more informative a study is. Where available,
the correlations between PM10
and PM2.5,
and between PM10 and coarse
PM are also given. Some studies have addressed
effects of coarse particles on morbidity
endpoints.
These will also be reviewed.
Effects of coarse
particles on mortality
The results of time series studies on
effects of fine and coarse particles on
mortality are summarized in Table
2.
Six Cities study,
United States of America
The original study by Schwartz et al.
(1997) was essentially replicated by Klemm
et al. (2000). This is still the study
with the largest number of observations,
around 190 000 deaths observed over a
number of years in six towns in the United
States of America. In this study, fine
PM was associated with mortality but coarse
PM was not. Of interest is that in the
one town where CM was found to be associated
with mortality (Steubenville), the correlation
between FP and CM was high at 0.69. No
two-pollutant analysis of these data has
been reported.
Santiago, Chile
Cifuentes et al. (2000) analysed a large
database from Santiago, Chile where PM
levels where high. Both FP and CM were
associated with mortality, but in a two-pollutant
model containing both FP and CM, the association
with FP was unchanged, whereas the association
with CM all but disappeared.
Philadelphia, United
States of America
Lipfert et al. (2000) re-analysed data
from Philadelphia and surrounding areas,
and found associations between mortality
and fine and coarse PM of roughly similar
magnitude, although the associations with
CM were mostly not significant. The paper
contains a large number of estimates without
standard errors or confidence intervals,
the denominator of which is given as “means
minus 4th percentile”; there are
various means, but no 4th percentiles
reported. The Environment Protection Agency’s
fourth draft version of the PM criteria
document has calculated effect estimates
which are in the order of a 1.6% increase
in cardiovascular mortality per 10 µg/m3
for both metrics, being significant for
fine but not for coarse PM (US EPA, 2003).
Eight cities, Canada
In a study conducted in eight Canadian
cities, Burnett et al. (2000; 2003) found
both fine and coarse PM to be associated
with mortality; no attempt was made to
adjust these associations for each other.
The effect estimates in the table
[2] are from the recent re-analysis
report (Burnett et al., 2003). That report
contains a variety of estimates, which
show fairly similar estimates for fine
and coarse mass in the range of 0.6 to
1.5 % increase in mortality for each 10
µg/m3 increase in particle
mass. The correlations between PM10
and PM2.5
and coarse mass respectively were much
higher than the correlation between fine
and coarse PM.
Santa Clara County,
California, United States of America
Fairley et al. (1999; 2003) analysed a
small number of deaths in Santa Clara
County, California, and found mortality
to be associated with fine but not coarse
particles. The effect estimates in the
table
[2] are from re-analysed data, using
“new GLM”. The correlations
between PM10 and PM2.5
and coarse mass respectively were much
higher than the correlation between fine
and coarse PM.
West Midlands Conurbation,
United Kingdom
A study from the United Kingdom by Anderson
et al. (2001) found no association between
mortality and either fine or coarse PM.
However, in season-specific analyses there
was a significant association with fine
but not coarse PM in the warm season.
The correlations between PM10
and PM2.5
and coarse mass respectively were much
higher than the correlation between fine
and coarse PM.
Mexico City, Mexico
Castillejos et al. (2000) analysed three
years of mortality in a section of Mexico
City where coarse PM measurements were
available. Both fine and coarse mass were
associated with mortality, but in a two-pollutant
model, coarse mass was clearly dominant.
The authors speculated that there was
much biogenic contamination in the coarse
mass fraction.
Wayne County, Michigan,
United States of America
In a small study in Wayne County conducted
over the 1992–1994 period, fine
and coarse PM were both not significantly
associated with mortality. The effect
estimate for coarse mass was somewhat
larger than for fine mass (Lippmann et
al., 2000; Ito et al., 2003). As was found
in other investigations, the correlations
between PM10 and PM2.5
and coarse mass respectively were much
higher than the correlation between fine
and coarse PM.
Coachella Valley,
California, United States of America
In a study conducted in the arid Coachella
Valley, Ostro et al. (2000, 2003) found
evidence for effects of fine particles
(but not coarse particles) on total mortality.
When the analysis was restricted to cardiovascular
mortality, there was a significant association
with coarse but not fine particles, although
the effect estimate for fine particles
was still much larger than for coarse
PM. The results were generally unaffected
by model specification (Ostro et al.,
2003). In the re- analysis published in
2003, the authors looked at cardiovascular
mortality only, so that no comparison
is possible with the original report with
respect to total mortality. Again, correlations
between PM10 and fine and coarse
mass respectively were higher than the
correlation between fine and coarse PM.
Phoenix, Arizona,
United States of America
In a small study from Phoenix, Arizona,
where coarse PM is higher than fine PM
due to arid conditions, both were found
to be associated with cardiovascular mortality
at lag 0 (Mar et al., 2000, 2003). At
lag 1 the association was stronger for
fine (7.1% per 10 µg/m3,
95% confidence intervals: 1.1–12.9%)
than for coarse particles (1.6% per 10
µg/m3, 95% confidence
intervals: 0.5–3.8%). Again, correlations
between PM10
and fine and coarse mass respectively
were higher than the correlation between
fine and coarse PM.
Another small study over
a one year period in Atlanta has been
reported (Klemm et al., 2000), with about
8400 deaths, showing no effect whatsoever
although coefficient and t-statistic (t=1.15)
for fine PM were larger than for coarse
PM (t=0.21).
Schwartz analysed a time
series of mortality data from Spokane,
Washington where dust storm regularly
occur. He found that on dust storm days
(which had an average PM10
concentration of 263 µg/m3),
there was no increased mortality compared
to control days which had an average PM10
concentration of 42 µg/m3
(Schwartz et al., 1999).
The American Cancer Society
(ACS) cohort
study conducted in the United States
found no evidence that coarse PM was associated
with mortality over long periods of follow-up
(Pope et al., 2002). This is an important
observation because the health impact
assessments within CAFE and the proposed
annual average limit values for fine PM
rely in part on the mortality effects
seen in this and some other cohort studies.
Conclusion on
coarse PM and mortality
There is some evidence for effects of
coarse PM on mortality. This is most clear
in studies from arid regions (Phoenix,
Coachella Valley, Mexico City) where PM
concentrations are relatively high. Studies
from the Detroit area and from Canada
also provide some support for an effect
of coarse PM on mortality. Few studies
have analysed fine and coarse PM jointly.
Two studies that did so (from Santiago,
Chile, and Santa Clara County, California)
showed that effects of coarse PM completely
disappeared after adjustment for fine
PM. In both studies, the effects of fine
PM remained after adjustment for coarse
PM. One study from Mexico City found the
opposite: coarse PM effects remained,
but fine PM effects did not. The correlation
between fine and coarse PM in all of these
studies was moderate at values between
0.28 and 0.59 with one higher value at
0.69 in Steubenville. In contrast, the
correlations between PM10
and fine as well as coarse PM was much
larger in all studies. Usually, correlations
between PM10 and fine PM were
largest, but there were some exceptions,
notably from arid areas where PM10
was dominated by coarse PM. The implication
is that analyses based on PM10
are generally unable to support statements
on the relative importance of fine and
coarse PM. The modest correlations between
fine and coarse PM on the other hand do
allow separation of the two effects. It
is unfortunate that so far, all but a
few studies have failed to report the
results of two-pollutant analyses.
There is only one report
from Europe at this point. This study
from the United Kingdom found no effect
of either fine or coarse PM on mortality.
However, in the warm season, significant
effects of fine but not coarse PM were
observed.
The ACS cohort
study did not show an effect of spatial
variations in coarse particles on mortality.
Effects of coarse
particles on morbidity
A study of respiratory hospital admissions
from Washington State (Schwartz, 1996)
found an association with PM10.
This association which was not significantly
smaller in the autumn period when PM10
was suggested to be dominated by wind
blown dust. One would expect a smaller
association if wind blown dust was innocuous.
A more recent study from the same area
found that asthma
hospital admissions were associated with
fine as well as coarse particles, which
were only moderately correlated at 0.43
(Sheppard et al., 1999).
A study from Anchorage,
where PM10
is dominated by coarse crustal material,
found significant effects of PM10
on outpatient visits for asthma, bronchitis
and upper respiratory
tract infections (Gordian et al.,
1996).
Another study from Washington
State found a small increase in respiratory
hospital admissions after dust storms
during which maximum 24 hour PM10
concentrations exceeded 1000 µg/m3
(Hefflin, 1994). Coefficients were estimated
to be about 3–4% per 100 µg/m3,
which is not very different from coefficients
estimated from large time series studies
on PM and hospital admissions.
In a study among school
children (Schwartz & Neas, 2000),
fine particles were found to be associated
with reduced peak flow and increased lower
respiratory symptoms. Independently,
coarse particles were only associated
with increased cough, which was attributed
to the irritative potential of coarse
particles in the respiratory tract.
In a recent study from
Toronto, asthma hospitalizations among
6–12-year-old children were found
to be associated with coarse particles
more strongly than with fine particles
(Lin et al., 2002).
Analyses conducted within
the Children’s Health Study in southern
California found no evidence of an association
between coarse PM and bronchitic symptoms
in a prospective assessment of children
with asthma (McConnell et al., 2003).
In the same study, NO2 and
organic carbon were the pollutants most
closely associated with symptoms. The
correlation between annual average PM2.5
and coarse particles was only 0.24, whereas
PM10 was highly correlated
with both at 0.79. This analysis took
into account both within and between community
variations over a four year period. This
illustrates that separate assessment of
associations with fine and coarse PM is
possible when both are actually measured.
Earlier publications from this cohort
found some evidence of an effect of coarse
PM on lung
function growth that was inseparable
from effects of other particle metrics
(Gauderman et al., 2000, 2002). However,
in these analyses the within- community
variation in air pollution exposures over
time was not taken into account, and correlations
between PM10, coarse and fine
particles were much higher for this
reason than in the analysis of bronchitic
symptoms among children. In areas of Europe
where roads are being sanded, and studded
tyres are used in winter, episodes of
high so-called “spring dust”
concentrations occur when the snow melts.
One study from Finland has addressed possible
health consequences (Tiittanen et al.,
1999). TSP, PM10 and PM2.5
were measured, and coarse mass was estimated
by subtracting PM2.5
from PM10. Median concentrations
were 57, 28, 15 and 8 µg/m3
respectively, but maximum concentrations
were 234, 122, 55 and 67 µg/m3
(24 hour average). Correlations between
the different particle metrics were very
high at 0.90–0.98 in this study
so that they could not be separated in
the analysis. Morning peak flow and cough
were found to be associated with all of
these particle metrics (except TSP which
was not analysed) in a panel of asthmatic
children. Because of the high correlations
between metrics, no firm conclusions with
respect to an independent role of coarse
PM can be drawn.
In the time series study
from the United Kingdom quoted earlier
(Anderson et al., 2001), none of the particle
metrics analysed had a clear relationship
with respiratory and cardiovascular hospital
admissions.
A study from eight districts
in four cities in China reported that
the prevalence of respiratory symptoms
in children was more strongly associated
with TSP, and with coarse than with fine
particles. Mean concentrations were high
at 356 µg/m3 for TSP,
and 151, 92 and 59 µg/m3
for PM10,
PM2.5
and coarse mass respectively (Zhang et
al., 2002).
Conclusion on
coarse PM and morbidity
A few studies have found associations
between respiratory morbidity endpoints
and coarse particles in areas where no
such associations with mortality were
found. Evidence suggests that the irritative
potential of coarse particles might be
sufficient to cause respiratory morbidity
leading to increases in hospital admissions.
Some of these studies were conducted in
areas where coarse PM is low, e.g. Seattle
where the median and 90th percentile of
the CM distribution were 14 and 29 µg/m3
respectively (Sheppard et al., 1999).
The number of time series
studies that have addressed effects of
coarse PM seems too limited at the moment
to allow derivation of exposure-response
relationships. The sparse data reported
show that effect estimates were sometimes
of the same order as those for fine PM.
Application of two-pollutant analyses
in databases from which this has not yet
been reported is urgently needed to address
the question whether effects of coarse
PM remain after adjustment for fine PM.
Very few data exist that
allow estimates of long term effects of
coarse PM on morbidity. One study from
China, conducted at high levels of exposure,
suggests that the prevalence of respiratory
disease among children is especially associated
with coarse PM.
Table
2: Summary of time series relating coarse
particulate matter to mortality
Source
& © : WHO
Regional Office for Europe  Health
Aspects of Air Pollution
- answers to follow-up questions from
CAFE (2004), Question 8
|
2.
How does Particulate Matter (PM) affect
human health? 
