ARTICLE IN PRESS
Atmospheric Environment 39 (2005) 307–314
www.elsevier.com/locate/atmosenv
Long-term PAH accumulation after bud break in Quercus ilex
L. leaves in a polluted environment
Anna Alfania,, Flavia De Nicolaa, Giulia Maistoa, Maria Vittoria Pratib
a
Dipartimento di Biologia Vegetale, Università degli Studi di Napoli Federico II, via Foria 223, 80139 Napoli, Italy
b
Istituto Motori del CNR, via Marconi 8, 80125 Napoli, Italy
Received 1 October 2003; accepted 8 September 2004
Abstract
The dynamics of polycyclic aromatic hydrocarbon (PAH) concentrations in the leaves of Quercus ilex L. for 16
months after bud break (May 2001–September 2002) were studied at a polluted site in the urban area of Naples by
comparison to the dynamics at a control site in the Vesuvius National Park. Twenty-seven PAHs were extracted by
sonication and quantified by GC-MS. Total PAH concentrations in the leaves sampled at the urban site showed a
considerable increase from bud break, with the highest values during the winter (about 3-fold greater than the initial
value) and a subsequent decrease, unlike the control site. The control site exhibited PAH concentrations one order of
magnitude lower than the urban site. At the urban site, the medium molecular weight PAHs, amounting to 72% of the
total, appear responsible for the temporal trend, while the low and high molecular weight PAHs (respectively, 10% and
18%) exhibited only narrow variations over time. At the control site, the low, medium and high molecular weight PAHs
contributed similarly to the total concentrations (32%, 31% and 37%, respectively); the low molecular weight PAHs
showed the widest temporal variations. Carcinogenic PAHs showed a dynamic at the urban site comparable to that
shown by the total PAHs. At the control site dibenzo(a,h)anthracene exhibited concentrations higher than at the urban
site.
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Polycyclic aromatic hydrocarbons; Air contamination; PAH leaf accumulation; PAH dynamics; Carcinogenic PAHs
1. Introduction
Vegetation is exposed to dry and wet deposition of
pollutants. It thus represents a sink of inorganic and
organic compounds. Various plants have been found to
accumulate polycyclic aromatic hydrocarbons (PAHs)
both in experimental research and in situ (Alfani et al.,
2001; Howsam et al., 2000, 2001; Jouraeva et al., 2002;
Müller et al., 2001; Nakajima et al., 1995; Wagrowski
and Hites, 1997). PAH root uptake from contaminated
Corresponding author. Fax: +39 081 2538523.
E-mail address: alfani@unina.it (A. Alfani).
soils was found to be negligible (Blum and Swarbrick,
1977; Edwards, 1986), so the main PAH accumulation
pathway is from the air to the leaf surface. Atmospheric
PAHs, both in gas phase and particle phase, may enter
leaves by absorption into the waxy cuticle or by stomata
uptake (Simonich and Hites, 1994). Leaf concentrations
can provide a time-integrated value of atmospheric
PAH concentrations. Accordingly, plant leaves may
represent a convenient passive sampler to monitor
atmospheric PAHs.
In recent years, PAHs have received particular attention because of their mutagenic and carcinogenic properties (EPA, 1992; IARC, 1987) and their monitoring is
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.atmosenv.2004.09.001
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regarded as necessary (European Communities, 1996).
The biomonitoring of PAH air concentrations through
leaf analyses is an economic and efficient system, but to
evaluate atmospheric PAH contamination using plant
leaves, it is necessary to determine the pattern of PAH
accumulation during leaf growth and the behaviour of
PAHs in the leaves. In previous studies on air PAH
biomonitoring (Alfani et al., 2001), high differences of
PAH accumulation were found in leaves of Quercus ilex
L. in the urban area of Naples, showing clear gradients
among the selected sites. In this paper, by sampling
Q. ilex leaves at regular intervals after bud break over a
16-month period, we aimed to highlight the dynamics
of PAH accumulation taking into account a series
of variables, such as leaf ageing, the influence of
meteorological conditions (temperature, rainfall) and
the temporal trend of air PAH concentrations. The
contribution of different molecular weight PAHs to total
leaf concentrations as well as the contribution of leaf
carcinogenic PAHs and the variation in the PAH profile
during the observation period were also considered.
2. Materials and methods
Q. ilex L., an evergreen Mediterranean oak, with
xeric, pubescent, lanceolate leaves, was selected for this
study. It is widely distributed throughout the Mediterranean region in natural and anthropic areas, showing
an ability to accumulate and retain airborne particulates
and thereby becoming a helpful biomonitor.
Samplings of Q. ilex leaves were carried out at two
sites: a square in Naples with a high vehicular traffic
flow, and a woodland in the Vesuvius National Park,
12 km from Naples, considered as a control.
At the urban and control sites, ten Q. ilex trees were
selected and, for every tree, four–six branches were
numbered and labelled; in order to collect leaves of the
same generation and from the same branches at each
sampling. The samples were collected at about 2 m
above the ground surface. From May 2001 to September
2002, every 2 months, three samples of leaves were
collected both at urban and control sites. Each sample
consisted of several leaves, each leaf being picked from a
labelled branch on the selected trees. The leaves were
removed by hand from the branches, and care was taken
to minimise contact with the leaf surface. The leaf
samples were placed in polyethylene bags and transported to the laboratory at ca. 4 1C and stored at 20 1C
until analysed. The first samples, collected in May 2001,
consisted of 2–3-week-old leaves, the last samples of
18-month-old leaves collected in September 2002.
During sampling, the leaves from the urban site
showed a conspicuous black deposit on the surface.
The leaves were not washed before PAH extraction, so
the data presented in this study are an expression of the
PAH concentrations of the leaves plus any particles
impacted and retained on the leaf surface.
The extraction procedure was carried out on defrosted
leaves. The leaf samples (ca. 5 g wet weight) was mixed
with equal quantities of sodium sulphate anhydrous.
A mix of deuterated PAHs (naphthalene D8, acenaphthene D10, phenanthrene D10, chrysene D10 and
perylene D12) were added before extraction for quantification. The samples were extracted in a mixture of
dichloromethane:acetone (1:1=v:v) by three consecutive
sonications (Misonix, XL2020). After the first sonication
(3 min) in 100 ml of mixture, the samples were recovered
by vacuum filtration and the extracts were stored in a
flask. The recovered samples were sonicated (3 min)
again, adding 100 ml of mixture, and consecutively a
third sonication (3 min) was carried out adding another
100 ml of the mixture. After the third sonication, the
samples were vacuum filtered and the extracts were
added to those from the first sonication. The extracts
were rotary evaporated to ca. 5 ml, filtered (0.2 mm), and
completely dried under a gentle nitrogen stream.
Subsequently, the extracts were diluted with 4 ml of
dichloromethane to be analysed.
The analyses were carried out by GC-MS (HewlettPackard 5890 GC with on-column manual injection,
coupled to Hewlett-Packard 5971 mass-selective detector, and equipped with an HP-5MS capillary column
30 m 0.25 mm i.d. with a 0.25 mm film thickness and a
phase ratio of 250). Oven temperature program was held
at 33 1C for 1 min, then ramped at 20 1C min 1 to 280 1C
and held for 15 min. The on-column inlet temperature
was set in oven track, with an injector temperature 3 1C
higher than the oven temperature at all times. The
carrier gas was helium at a constant flow rate of
1 cm3 min 1 during the analysis. The SIM (selected ion
monitoring) modality of acquisition was used.
The following 27 compounds were quantified after
a calibration curve had been performed for each
PAH: naphthalene, acenaphthylene, acenaphthene,
fluorene (low molecular weight PAHs), phenanthrene,
anthracene, fluoranthene, pyrene, 2,3-benzofluorene,
benzo(c)phenanthrene, benzo(g,h,i)fluoranthene, benzo(b)nafto(1,2-d)tiophene, ciclopenta(c,d)pyrene, benzo(a)anthracene,
chrysene+triphenylene
(medium
molecular weight PAHs), benzo(b+k+j)fluoranthene,
benzo(e)pyrene, benzo(a)pyrene, 1,3,5-triphenylbenzene,
perylene, indeno(1,2,3-c,d)pyrene, benzo(b)chrysene+
picene, dibenzo(a,c)anthracene, dibenzo(a,h)anthracene,
benzo(g,h,i)perylene, antantrene, coronene (high molecular weight PAHs).
The total PAHs reported in this study represent the
sum of the concentrations of all compounds. The
concentrations of all the investigated PAHs are calculated considering the recovery of deuterated PAHs. The
recoveries ranged from 40% to 80%, with the highest
losses for naphthalene and acenaphthene.
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240
The dynamics of the total PAH concentrations in Q.
ilex leaves over a period (May 2001–September 2002) of
16 months, after bud break, shows a conspicuous PAH
increase up to January 2002 at the urban site (Fig. 1).
Subsequently the concentrations decrease until July
2002, and do not show noticeable variations from July
to September 2002. The total PAH leaf concentrations
expressed as ng g 1 dry weight show a range between
1134 in July 2001 and 3482 in January 2002. The
decrease in PAH concentrations from May to July 2001
(Fig. 1) is misleading: in this period, the xeromorphism
of the young Q. ilex leaves starts to become accentuated
and the leaf dry weight per fresh weight increases (Fig. 1,
box). At the control site, leaf PAH concentrations
appear lower than at the urban site and the temporal
variations are narrow. The concentrations range from
240 to 647 ng g 1 dry weight, with the lowest concentration in March 2002 and the highest in November 2001
(Fig. 1).
Rainfall and temperature patterns in Naples during
the sampling period (Fig. 2) show a warm, dry summer
and cold, rainy winter in 2001; the summer in 2002
appears particularly rainy.
The contribution of different molecular weight PAHs
(low, medium and high), as reported by Harner and
Bidleman (1998), to the total concentrations at the
urban site differs over the study period (Fig. 3).
At the urban site, the medium molecular weight PAHs
increase 3-fold from May 2001 to January 2002 and then
decrease until September 2002, reaching roughly the
values of May 2001. The trend of the medium molecular
200
160
120
80
40
40
20
T (°C)
Precipitations (mm)
3. Results
0
0
M J J A S O N D J F M A M J J A S
Fig. 2. Rainfall (bars) and temperatures (black triangles)
applicable to the urban and control sites from May 2001 to
September 2002.
4000
400
control site
urban site
200
PAH (ng g-1 d. w.)
3000
0
MJ S N J MMJ S
2000
1000
Sept 02
July 02
May 02
Mar 02
Jan 02
Nov 01
Sept 01
July 01
May 01
0
Fig. 3. Dynamics of low (white triangles), medium (white
circles) and high (black diamonds) weight PAH concentrations
(7s.e.) in Q. ilex leaves at the urban and control (in the box)
sites.
4000
0.8
0.6
0.4
PAHtot (ng g-1 d.w.)
3000
0.2
0.0
leaf d.w./leaf w.w.
MJ S NJ M MJ S
2000
1000
Sept 02
July 02
May 02
Mar 02
Jan 02
Nov 01
Sept 01
July 01
May 01
0
Fig. 1. Dynamics of total PAH concentrations (7s.e.) in Q.
ilex leaves at the urban (black circles) and control (white
triangles) sites. In the box, the dry/wet weight ratios in Q. ilex
leaves at the urban and control sites are indicated.
weight PAHs was the same as the total PAH concentrations. Low and high molecular weight PAHs show only
small variations at this site and differ from the trend of
total PAHs (Figs. 1 and 3). At the control site, the low
molecular weight PAHs exceed the values of the other
two groups from May to November 2001, unlike that at
the urban site (Fig. 3, box).
Table 1 shows the percentage of low, medium and
high molecular weight PAHs in the leaves for each
sampling, both at the control and urban sites. The mean
percentages over the study period are also reported. At
the urban site the medium molecular weight PAHs
constitute the highest fraction (72%), while the low and
high molecular weight PAHs represent, respectively,
10% and 18% of the total concentrations (Table 1). At
the control site the low, medium and high molecular
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Table 1
Q. ilex leaf concentrations of low, medium and high molecular weight PAHs (LMW, MMW and HMW, respectively) and carcinogenic
PAHs as percentages of totals during the studied period at urban and control sites; mean values over time are also reported
2001
2002
Mean
May
July
September
November
January
March
May
July
September
Urban site
LMW
MMW
HMW
Carcinogenic
14.30
73.60
12.10
9.24
9.80
70.59
19.61
13.88
19.70
62.10
18.20
10.42
8.71
82.85
8.44
9.94
4.75
82.44
12.81
7.71
4.36
79.17
16.47
10.74
8.97
66.56
24.47
13.82
11.28
63.28
25.45
12.73
9.36
69.70
20.94
11.35
10.1
72.3
17.6
11.1
Control site
LMW
MMW
HMW
Carcinogenic
56.59
28.94
14.46
10.96
39.55
19.77
40.69
34.02
63.03
15.34
21.63
15.54
54.11
26.28
19.61
15.46
12.05
53.71
34.24
20.29
11.44
44.15
44.41
23.57
12.73
29.27
58.00
32.69
25.78
29.57
44.65
14.50
15.02
33.96
51.02
10.25
32.3
31.2
36.5
19.7
1000
150
350
urban site
control site
280
control site
140
PAH (ng g-1 d.w.)
600
M J S N J MM J S
400
PAHcarc (ng g-1 d. w.)
50
70
0
urban site
100
210
800
150
100
0
M J S N J MM J S
50
200
0
Sept 02
July 02
May 02
Mar 02
Jan 02
Nov 01
Sept 01
July 01
May 01
Sept 02
July 02
May 02
Mar 02
Jan 02
Nov 01
Sept 01
July 01
May 01
0
Fig. 4. Dynamics of phenanthrene (black circles), fluoranthene
(black triangles), pyrene (inverted black triangles), benzo(g,h,i)fluoranthene (white circles), chrysene+tryphenylene (white
diamonds) and naphthalene (white squares) concentrations
(7s.e.) in Q. ilex leaves at the urban and control (in the box)
sites.
Fig. 5. Dynamics of carcinogenic PAHs: benzo(a)anthracene
(black circles), benzo(b+k+j)fluoranthene (black triangles),
benzo(a)pyrene (inverted black triangles), indeno(1,2,3-c,d)pyrene (white circles), dibenzo(a,h)anthracene (white diamonds)
concentrations (7s.e.) in Q. ilex leaves at the urban and control
(in the box) sites.
weight PAHs constitute, respectively, 32%, 31% and
37% of the total (Table 1).
At the urban site, over the studied period, the 3–4 ring
PAHs (pyrene, fluoranthene and phenantrene) exhibit
the highest concentrations among the medium molecular
weight PAHs (Fig. 4), making up from 30% to 60% of
the total PAHs. At the control site, naphthalene shows
the highest concentrations among the low molecular
weight PAHs, with values higher than at the urban site,
particularly from May to November 2001 (Fig. 4, box).
Among the studied PAHs the benzo(a)pyrene, benzo(b+k+j)fluoranthene, indeno(1,2,3-c,d)pyrene, benzo(a)anthracene and dibenzo(a,h)anthracene represent
the carcinogenic PAHs. The dynamics of these are
shown in Fig. 5.
At the urban site, the highest concentrations were
found in November 2001 and January 2002 with
elevated values of benzo(b+k+j)fluoranthene, benzo(a)anthracene and dibenzo(a,h)anthracene, with
the same trend shown by the total PAH dynamics.
The benzo(b+k+j)fluoranthene concentrations increase
from May 2001 to January 2002 and remain high
until September 2002. Benzo(a)anthracene and
dibenzo(a,h)anthracene show a peak in November
2001 and then decrease with different trends. Indeno(1,2,3-c,d)pyrene and benzo(a)pyrene appear to have
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the lowest and most constant concentrations over time
(Fig. 5). At the control site dibenzo(a,h)anthracene
shows even higher concentrations than at the urban site.
The concentrations of the other carcinogenic PAHs
appear more constant and lower than at the urban site
(Fig. 5, box).
4. Discussion
PAH concentrations of Q. ilex leaves at the site in
Naples are high, showing in January 2002 values about
7-fold higher than at the control site, highlighting a
conspicuous accumulation of airborne PAHs in leaves in
the urban area. These high PAH accumulations in leaves
are in broad agreement with the dense covering of hairs
on both adaxial and abaxial Q. ilex leaf surfaces that
have been shown to be effective at trapping particles
(Alfani et al., 1997; Rauret et al., 1994). Indeed leaves
with hairs present a larger surface and boundary
layer than hairless leaves, enhancing the potential
for capture and retention of PAHs from the air
(Howsam et al., 2000).
PAH leaf accumulation provides a temporal integration of PAH air pollution (Alfani et al., 2001; Howsam
et al., 2001; Simonich and Hites, 1995; Tremolada et al.,
1996; Wagrowski and Hites, 1997). In particular, leaf
PAH concentrations of Laurus nobilis L., another
evergreen Mediterranean species like Q. ilex, from 13
urban sites in Tuscany (Italy) proved to be correlated to
air PAH concentrations collected at the same sites
(Lodovici et al., 1998).
At the urban site Q. ilex leaves showed PAH
concentrations 3-fold higher than at the control site
already in May 2001, 2–3 weeks after bud break.
Similarly, trace metal concentrations accumulated rapidly in new leaves of Q. ilex at a polluted site in Naples
(Alfani et al., 1996). The active metabolism of Q. ilex
leaves, after bud break, probably enhanced foliar uptake
of PAHs whose high concentrations in the urban area
can be attributed to vehicular traffic. Absorption and/or
adsorption of PAHs by leaves has been found to be very
quick in young leaves exposed to PAH contaminated air
(Simonich and Hites, 1994). On the other hand, the
increase in leaf lipid and cuticular waxes facilitates
accumulation in the leaves of PAHs, lipophilic compounds, as shown by the increase in PAH concentrations during leaf growth at the Naples urban site.
Moreover, Brabec et al. (1981) and Little and Wiffen
(1977) showed that senescent leaves of a species were
more effective at retaining airborne metals and particles
than non-senescent ones.
Leaf PAH concentration continues to increase during
the winter, and in January at the urban site the value is
about 4-fold higher than in July and one order of
magnitude greater than at the control site. This trend is
311
in broad agreement with that of PAH concentrations
found in mature Q. ilex leaves from six sites of the
Naples area in the same period (De Nicola et al.,
unpublished data). These concentration data show that
PAH leaf accumulation does not change appreciably
depending on the age in mature leaves of Q. ilex, and
therefore reflect the degree of contamination of the
atmospheric PAHs in the studied area. Total PAHs as
well as their profile do not change with respect to leaf
ageing. Only during the first 2 months after bud break,
when the leaves do not exhibit xeromorphism, is
pollutant accumulation likely to be faster. Mature
xeromorphic leaves of Q. ilex appear good monitors at
each time during ageing. Moreover, both the increase in
total PAH concentrations in the leaves of Q. ilex in
winter and the decrease in the summer appear consistent
with the seasonal pattern found by Caricchia et al.
(1999) in the air particulate collected in two sampling
campaigns at several sites in the urban area of Naples.
Also in other cities, higher PAH concentrations directly
in the particulate (Lodovici et al, 2003; Menichini et al.,
1999; Wada et al., 2001) or in plant leaves (Lodovici
et al., 1998; Nakajima et al., 1995) have been found
in winter than in summer.
During the winter, the higher air concentrations of
PAHs are due to increases in sources, both in number
and magnitude, compared with the summer (Howsam
and Jones, 1998; Park et al., 2002). The degradation
reaction rate of PAHs in air, lower in winter than in
summer (Halsall et al., 2001), contribute to produce a
particularly high PAH burden in wintertime.
The decrease in PAH concentrations, both in
suspended particulate matter and in leaf tissues,
reported by many investigators (Caricchia et al., 1999;
Lodovici et al., 2003; Howsam et al., 2001; Nakajima et
al., 1995; Wada et al., 2001), has been attributed to
elevated PAH photodegradation in summer, caused by
strong sunlight, high temperature and high ozone
concentrations (Lodovici et al., 2003; Papageorgopoulou et al., 1999), especially in the Mediterranean region.
McCrady and Maggard (1993) have shown that photodegradation is a significant removal mechanism at the
leaf surface. Lower PAH concentrations in the leaves of
Q. ilex sampled in Naples during the warmest months
support the theory of photo- and thermodegradation of
PAHs. It has been proposed that PAHs adsorbed on
plant surfaces are volatilised as temperatures rise
(Halsall et al., 2001) and are degraded, particularly
after reactions with hydroxyl radicals, to a greater extent
in summer than in winter (Niu et al., 2003).
The plentiful and frequent rains recorded during the
investigated period are unlikely to affect leaf PAH
concentrations. Indeed, the highest leaf PAH concentrations were measured in winter 2001 when more plentiful
rains but lower temperatures than the next summer were
recorded. Moreover, leaves washed in distilled water did
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not show variations in PAH concentrations with respect
to unwashed leaves (unpublished data; Lodovici et al.,
1998).
In the leaves of Q. ilex from the urban site, the
medium molecular weight PAHs, representing the highest fraction (mean 72%) of the total, appear responsible
for the increase and the subsequent decrease of total
PAH concentrations.
The condensate of vehicle exhausts is relatively
enriched in fluoranthene, pyrene, benzo(g,h,i)perylene
and coronene; of these the first two, medium molecular
weight PAHs, appear particularly accumulated in leaves
of Q. ilex at the urban site, where the effect of traffic
flow is high. Phenanthrene, fluoranthene and pyrene, the
highest accumulated PAHs in Q. ilex leaves, are also the
three most abundant PAHs in the moss Tortula muralis
at the urban area of Ferrara especially in the industrial
sector (Gerdol et al., 2002). Diamond et al. (2000) found
these same three compounds as the most abundant
PAHs also in an organic film on an urban surface.
At the control site, naphthalene, a low molecular
weight PAH, shows the highest concentrations. The low
molecular weight PAHs constituted a much higher
fraction of total PAHs both in leaves (Alfani et al.,
2001; Wagrowski and Hites, 1997) and moss (Gerdol
et al., 2002) from rural areas.
The sources of emissions, the distance from the source
and the physico-chemical properties of the single PAHs,
that control the partition of each PAH between gaseous
and particulate phase and thus determine their mobility
and transport, affect the air concentrations of each
PAH. These factors result in lower values at the control
site compared to the urban site and different contributions of single compounds to the total, as a function of
site typology. In urban areas, motor vehicle exhaust is
the principal source of PAHs (Alfani et al., 2001;
Katz and Chan, 1980; Nielsen, 1996; Takada et al.,
1990; Valerio et al., 1992). Low molecular weight
compounds, in the vapour phase, are more widely
dispersed (Yang et al., 1991) and may represent
potential contaminants for remote areas. Indeed, at the
control site they exhibit a higher percentage of the total
than at the urban site.
Carcinogenic PAHs show different trends between the
urban and control sites. Dibenzo(a,h)anthracene unexpectedly exhibits higher concentrations at the control
than at the urban site, over the period July 2001–May
2002. The high concentrations of dibenzo(a,h)anthracene at the control site are responsible for the higher
percentage of carcinogenic to the total PAHs, compared
to the urban site. All the other carcinogenic PAHs show
higher values at the urban than the control site, with an
increase during the winter and a decrease in summertime. This concentration decrease is not exhibited by
benzo(b+k+j)fluoranthene either at the control or
urban sites.
The occurrence of some PAHs in remote areas is
explained mainly by aerial transport from distant
anthropogenic sources. On the basis of our findings,
this appears likely for naphthalene but is less evident for
dibenzo(a,h)anthracene. Indeed, the period of elevated
naphthalene leaf concentrations at the control site is
connected with the period of high PAH leaf concentrations also at the urban site, even if naphthalene leaf
concentrations in the latter are lower. Dibenzo(a,h)anthracene leaf concentrations do not show parallel
dynamics at the two sites; moreover the highest
concentrations were detected at the control site.
Lodovici et al. (1998) found a positive and significant
correlation between carcinogenic PAH levels in air and
the carcinogenic PAH concentrations in L. nobilis
leaves. Plant pollutant accumulation has been particularly useful for identifying unknown point sources, as
reported by Simonich and Hites (1995). The high
concentrations of dibenzo(a,h)anthracene in Q. ilex
leaves from the control site in the Vesuvius National
Park most likely indicate a natural or anthropic source
that calls for further research.
5. Conclusions
The leaves of Q. ilex, a Mediterranean evergreen oak,
show a considerable capacity to accumulate in situ
PAHs. Young leaves accumulate PAHs rapidly, within
2–3 weeks from bud break, already showing clear
differences between sampling sites at different pollutant
loads. Mature leaves (at full development) exhibit a
sharp seasonal trend in PAH contamination, as characterised in polluted habitats by air particulate analyses,
with increases in the winter season and decreases in
summertime. The differences between the control and
the urban sites, not only in total and different molecular
weight PAH concentrations but also in temporal
dynamics, are also evident.
Q. ilex mature xeromorphic leaves are useful in
determining regional PAH air contamination and, if
sampled over time, can indicate changes in contamination trends at every site in the monitored area.
Acknowledgements
This research was funded by the Ministry for Higher
Education and Scientific Research—MURST (PRIN
2000—MM05188955_001).
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