Environ. Sci. Technol. 2004, 38, 4739-4744
Historical Records of Airborne
Polycyclic Aromatic Hydrocarbons by
Analyzing Dated Corks of the Bark
Pocket in a Longpetiole Beech Tree
QIUQUAN WANG,* YULI ZHAO,
DONG YAN, LIMIN YANG,
ZHENJI LI, AND BENLI HUANG
Department of Chemistry and the MOE Key Laboratory of
Analytical Sciences, Xiamen University,
Xiamen 361005, China
Historical monitoring of airborne polycyclic aromatic
hydrocarbons (PAHs) pollution levels was novelly
demonstrated by analyzing the dated corks of a bark
pocket formed from 1873 to 2003 in a Longpetiole Beech
(Fagus longipetiolata) tree trunk sampled from southeastern
China. The fundamental studies indicated that the PAHs
of log Koa < 8.5 are primarily accumulated through interactions
with lipid substances in cork and log Koa dependent,
while the PAHs of log Koa > 8.5 existing as particlephase dependent on log Vp are accumulated through
stochastic entrapment by the lenticels on the surface of
the cork. The translocation of PAHs by xylem flow and phloem
stream as well as radial diffusion from the cork to the
inner tissues was not significant, and the cork is most
effective for accumulating airborne PAHs. The total
concentrations of 16 EPA PAHs (ΣPAHs) in the dated
corks progressively increased from 43.5 ng/g recorded in
the earliest available cork in 1873-1875 to the maximum 345.7
ng/g in 1956-1961, and then gradually decreased to
267.0 ng/g in 2003, while the concentration of perylene
(PER) was slightly fluctuating at 0.178 ( 0.033 ng/g. Moreover,
the concentration ratio of ΣPAHs to PER increased from
193 to 2431 from 1873 to 2003, indicating a progressive increase
in PAH pollution in southeastern China.
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are one class of
persistent organic pollutants (POPs). In the environment,
PAHs have both natural and anthropogenic sources. Natural
sources including forest fires, volcano activities, and biosynthesis by bacteria and plants, etc., contribute to the
background level of PAHs in the environment. However,
anthropogenic sources such as incomplete combustion of
fossil fuels, waste incineration, vehicle exhausts, and industrial processes, etc. are the predominant emission sources
of PAHs. Because PAHs are semivolatile, airborne PAHs may
exist in both particle and gas phases. The atmosphere is a
major pathway for the transportation and deposition of
natural and anthropogenic airborne PAHs (1) and has been
proven to be the primary source to be accumulated in
vegetation (2-4). As a consequence, various plants such as
moss, lichen, leaves, and tree bark have been employed as
bioindicators to monitor airborne PAHs pollution levels.
* Corresponding author phone: + 86 592 218 1796; fax: +86 592
218 3052; e-mail: [email protected].
10.1021/es049685j CCC: $27.50
Published on Web 08/18/2004
 2004 American Chemical Society
Tree bark accumulates airborne pollutants, which are
retained over time (5-8), and tree bark has been recently
employed as a bioindicator of airborne inorganic and organic
pollution levels (9-14), substituting for direct atmospheric
sampling methods. Furthermore, tree bark pockets, which
are formed in a tree trunk during growth by one of four
possible ways (i.e., recovery of a physical wound on the
surface of a tree trunk, between the joint of adjacent branches,
by inclusion of a cut branch or by an irregular shaped trunk),
have been demonstrated to be valuable for historical
monitoring of inorganic air pollutants by Satake et al., Bellis
et al., and Wang et al. (15-19). However, literature with regard
to the temporal monitoring of airborne POPs pollution by
the tree bark pocket (20) is somewhat sparse.
In this study, we aimed to establish a novel method for
the historical monitoring of airborne PAHs pollution by using
tree bark pockets. Their accumulation and distribution as
well as translocation among the tissues of the Camphor
(Cinnamomum camphora) tree trunk (southeastern China)
were intensively investigated based on the physiological
features of the tree trunk tissues, physicochemical properties
of PAHs, and correlations between PAHs’ concentration in
the tree trunk tissues, in corresponding airborne total
suspended particles (TSP) and in the host soil. Historical
change in airborne PAH pollution in southeastern China was
demonstrated by the dated corks of a bark pocket formed
from 1873 to 2003 in a Longpetiole Beech (Fagus longipetioleta) tree trunk. This is likely the first report on the regional
historical monitoring of airborne PAHs pollution levels by
tree bark pocket, so far. Such a methodology is expected to
be useful to the historic monitoring for other members of
airborne POPs in the environment.
Experimental Procedures
Sampling. Camphor tree (approximate 10-15 years old and
trunk diameter 15-20 cm) trunk tissues including cork, cork
cambium, cortex, phloem, vascular cambium, and xylem, as
well as the corresponding TSP and host soil, were collected
from the Xiamen campus of Xiamen University [longitude
118°05′23′′, latitude 24°26′24′′, altitude 2 m above sea level
(asl)], Nanjing (longitude 117°12′42′′, latitude 24°30′05′′,
altitude 437 m asl), Tianbao Rock (longitude 117°0′12′′,
latitude 25°50′51′′, altitude 580 m asl), and Wu Yi Shan City
(longitude 117°37′22′′, latitude 27°27′31′′, altitude 210 m asl),
where different pollution levels of airborne PAHs were
recognized. The Xiamen campus of Xiamen University is south
of the Xiamen urban area; the semitropical rainforest in
Nanjing is a national natural reservation, where the PAHs
concentrations can be regarded as the background values;
Tianbao Rock, another national natural reservation, lies in
Yongan adjacent to an industrial city of Sanming; Wu Yi Shan
City, a newly built city for travelers, is located next to the
national natural reservation of Wuyi Mountain. The four
sampling sites are shown in Figure 1. A section of the
Longpetiole Beech (F. longipetioleta) tree trunk containing
a bark pocket (shown in Figure 2) was sampled from a 147year-old Longpetiole Beech (tree trunk diameter, 0.7 m) felled
in July 2003 in Tianbao Rock, Fujian, southeastern China.
All the tree samples were collected from the trunk with
a clean chisel at a height of about 1.5 m, avoiding any moss
and lichen on the surface. Slices containing all tissues from
cork to xylem with an area of about 5 × 3 cm2 were sampled
from Camphor trees in the Xiamen campus, and each tissue
was consecutively peeled with a clean scalpel according to
the characteristic texture difference between adjacent layers
(Figure 3a), while for the Camphor tree samples from other
VOL. 38, NO. 18, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of sampling sites in Fujian Province, southeastern
China.
FIGURE 2. Bark pocket formed from 1873 to 2003 in a Longpetiole
Beech tree trunk sampled from Tianbao Rock National Natural
Reservation in July 2003.
sampling sites and the Longpetiole Beech bark pocket, only
corks were used. Corks were further sliced into three layers
with the depth range from 0 to 3, 3 to 5, and 5 to 8 mm. TSP
were collected on quartz fiber filter (diameter 4.7 cm,
Whatman), which was heated at 430 °C for 4 h and sealed
stored before use by a portable air sampler (Laoshan,
Qingdao, China) at a flow rate of 120 L/min for 12-16 h; the
sampler cutter head was at the height of about 2 m above
the ground. A total of 24 corresponding TSP samples were
seasonally collected at each site from March 2003 to May
2004 at the sites where the Camphor tree samples were
collected. Host soils were sampled within the top 20 cm just
around the foot of the trees, and the fraction of particle sizes
smaller than 2 mm was used for analysis after homogenization. A total of 26 cork samples was sliced from the
Longpetiole Beech bark pocket formed from the years of
1873-2003 at 0.5 cm intervals, each indicating an appropriate
period of time according to the annual rings around it.
Extraction and Cleanup. All tree tissue samples were
ground into small pieces. Before extraction, all samples were
spiked with a 100 µL internal standard solution of hexane
containing six full deuterated PAHs of naphthalene-d8 of 75
ng/mL, acenaphthene-d10 of 50 ng/mL, phenanthrene-d10
of 50 ng/mL, pyrene-d10 of 50 ng/mL, chrysene-d12 of 35
ng/mL, and benzene[a]pyrene-d12 of 20 ng/mL (Cambridge
Isotope Laboratories, Inc.) and then dried at 40 °C to constant
weight. Each weighed sample was packed in a clean filter
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 18, 2004
paper and was Soxhlet extracted with a 90 mL mixture of
hexane and methylene chloride (V/V ) 1:1) for 13 h. Each
extract was concentrated by a rotary evaporator (Shensheng
HB-5, Shanghai), and the solvent was exchanged to hexane
in 1 mL before clean-up by a glass column (1.0 cm i.d. × 30
cm in length) containing 8 g of silica gel (100-200 mesh,
Shanghai Chemical Reagents), which was activated by heating
at 130 °C for 16 h before use. The column was preequilibrated
with 50 mL of hexane before the sample extract was
transferred onto the column. The column was sequentially
eluted with 20 mL of hexane and a 30 mL mixture of
methylene chloride and hexane (V/V ) 3:7), to discard the
nonpolar impurity fraction of aliphatic hydrocarbons and
collect the fraction containing PAHs. The PAHs fraction was
concentrated with a rotary evaporator, and the solvent was
exchanged to hexane again. All hexane and methylene
chlorides were of pesticide-residue quality (Tedia) or analytical grade redistilled by a full glass apparatus. All samples
of TSP and soil were also extracted and purified following
the same procedures as the tree samples.
Analysis. The final volume of all samples was accurately
adjusted to 1.0 mL with hexane and analyzed by GCMSQP2010 (Shimadzu, Japan), which was equipped with a
capillary column of DB-17MS (30 m × 0.25 mm × 0.25 µm,
Agilent), and a nonpolar capillary column (5 m × 0.53 mm,
Alltech) was used as guard column. EPA 16 PAHs of
naphthalene (Nap), acenaphthylene (Acpy), acenaphthene
(Acp), fluorene (Flu), phenanthrene (PA), anthracene (Ant),
fluoranthene (FL), pyrene (Pyr), benz[a]anthracene (BaA),
chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IND), dibenz[a,h]anthracene (DBA), benzo[g,h,i]perylene (BghiP), and perylene (PER) were identified in scan
mode and quantified in selected ion monitoring (SIM) mode
with their molecular ions by internal standard calibration.
Sample injection was splitless with sampling time 2 min under
300 °C, and the injection volume was 1 µL. The oven
temperature program began at 60 °C and was held for 6 min,
ramped to 260 °C at 5 °C/min, where it was held for 18 min,
ramped at 5 °C/min to 280 °C and held for 10 min, and at
last ramped at 5 °C/min to 310 °C and held for 3 min. The
temperature of electron impact (EI) ionization source and
interface was kept at 200 and 300 °C, respectively. EPA 16
PAHs standards were purchased from ULTRA Scientific, Inc.
as a solution containing each of them as 1 µg/mL in methylene
chloride; PER (purity > 99.9%) was purchased from AccuStandard, Inc.
Blank tests were performed following the same procedures
used for the samples, and the concentrations of 16 EPA PAHs
were low enough to be insignificant except Nap 317.3 ng and
PA 7.78 ng. Triplicate runs for each sample were analyzed to
qualify the result, and all RSDs were below 15%. Determination limits (3σ) are in the range of 0.03 ng/g for Nap to 0.5
ng/g for BkF of the dry weight cork. The recoveries of the six
full deuterated PAHs internal standards were obtained to be
81 ( 12% (n ) 26) for naphthalene-d8, 92 ( 6% (n ) 26) for
acenaphthene-d10, 98 ( 8% (n ) 26) for phenanthrene-d10,
95 ( 5% (n ) 26) for pyrene-d10, 109 ( 5% (n ) 26) for
chrysene-d12, and 110 ( 9% (n ) 26) for benzo[a]pyrene-d12.
Results and Discussion
Distribution and Translocation of PAHs in Each Tissue of
a Camphor Tree Trunk. Vegetation may take up organic
chemicals either by aboveground tissues from the atmosphere (21) or by roots from the soil (22). For hydrophobic
POPs, such as PAHs, dibenzo-p-dioxins/dibenzofurans
(PCDD/Fs), polychlorinated biphenyls (PCBs), organochlorine pesticides, etc., roots uptake and translocation via xylem
have been shown negligible (23, 24), while atmospheric
deposition of these compounds to the aboveground parts
FIGURE 3. (a) Tree trunk structure and (b) distribution of the total concentration of 16 EPA PAHs in each tissue of a Camphor tree trunk.
TABLE 1. Concentrations of 16 EPA PAHs in TSP (ng/m3) and Camphor Tree Corks (ng/g) Collected from Wuyi Mountain, Nanjing
Rainforest, Tianbao Rock, and Campus of Xiamen University (XMU) as Well as Slope, Intercept, and Regression Coefficient (R2)
for the PAH Concentration in the Cork versus That in the Corresponding TSP
TSP (ng/m3) (n ) 24)
Nap
Acpy
Acpy
Flu
PA
Ant
FL
Pyr
BaA
Chr
BbF
BkF
BaP
IND
BghiP
DBA
linear regression
parameters
cork (ng/g) (n ) 3)
Wuyu Mt.
Nanjing
Tianbao Rock
XMU
Wuyu Mt.
Nanjing
8.64 ( 3.79
0.23 ( 0.12
0.96 ( 0.43
0.59 ( 0.28
1.74 ( 0.54
0.36 ( 0.11
0.64 ( 0.17
0.71 ( 0.18
1.04 ( 0.28
0.48 ( 0.12
0.60 ( 0.08
0.44 ( 0.08
0.71 ( 0.08
1.26 ( 0.22
1.02 ( 0.17
0.47 ( 0.06
6.54 ( 4.21
0.20 ( 0.09
0.71 ( 0.24
0.63 ( 0.29
1.82 ( 0.38
0.31 ( 0.18
0.53 ( 0.11
0.55 ( 0.13
0.91 ( 0.24
0.33 ( 0.11
0.24 ( 0.05
0.25 ( 0.04
0.21 ( 0.03
0.27 ( 0.04
0.18 ( 0.03
0.19 ( 0.02
2.91 ( 1.69
0.15 ( 0.07
0.52 ( 0.18
0.76 ( 0.31
1.66 ( 0.77
0.28 ( 0.11
0.38 ( 0.11
0.45 ( 0.10
0.85 ( 0.19
0.38 ( 0.12
0.28 ( 0.05
0.36 ( 0.06
0.25 ( 0.03
0.30 ( 0.04
0.24 ( 0.02
0.17 ( 0.03
2.93 ( 1.41
0.10 ( 0.05
0.26 ( 0.11
0.27 ( 0.10
0.78 ( 0.28
0.16 ( 0.06
0.28 ( 0.08
0.23 ( 0.07
0.78 ( 0.24
0.19 ( 0.05
0.16 ( 0.04
0.14 ( 0.03
0.15 ( 0.02
0.18 ( 0.03
0.12 ( 0.02
0.09 ( 0.01
73.1 ( 12.2
1.20 ( 0.32
17.32 ( 2.81
22.02 ( 3.37
109.8 ( 15.2
11.57 ( 1.71
65.31 ( 9.62
72.53 ( 9.46
8.84 ( 1.12
28.15 ( 4.01
9.96 ( 1.23
3.90 ( 0.53
8.15 ( 1.11
6.68 ( 0.96
7.52 ( 0.83
3.03 ( 0.42
41.75 ( 6.78
5.51 ( 1.84
13.99 ( 1.45
23.66 ( 3.21
84.65 ( 10.85
8.35 ( 1.34
39.22 ( 5.01
47.26 ( 6.23
7.65 ( 1.17
11.01 ( 1.24
4.51 ( 0.42
3.62 ( 0.31
4.53 ( 0.50
5.49 ( 0.64
3.40 ( 0.43
2.43 ( 0.37
occurs primarily by the processes of wet and dry deposition,
which can occur in either gas or particle phases (21). Figure
3b shows the distribution of the total concentration of 16
EPA PAHs in all tissues of the Camphor tree trunk. The results
indicated that tree cork has the greatest capability of
accumulating PAHs, and PAHs concentrations in it are
approximately 10 times higher than those in the tree xylem.
It might be ascribed to the high content of suberin in the
walls of the cork cells and the occurrence of lenticels on the
cork surface. Suberin is a class of fatty and waxy substances
composed of suberic acids and phellonic acids, which make
the cells impervious to water and restricts the exchange of
gases and nutrients. After the lipophilic airborne PAHs were
accumulated on the cork, they could be preserved over time.
In addition, for a mature tree, lenticel phellogen forms from
the cell interior to the stoma and is connected with the
adjacent cork cambium; cells are also produced on the outside
and in the inside from the lenticel phellogen. The outside
cells tend to round up, and intercellular gas space is inherently
formed, so that the tissue inside the lenticel is loosely packed.
The cells of the lenticel also tend to expand outside the tree
trunk, making the cork porous. Such properties make each
lenticel a pathway through which gas-phase PAHs can diffuse
to the living cells of the inner bark, while particle-phase PAHs
can also be entrapped into it (6). The decreasing gradient
from the outermost cork 1 (0-3 mm) to its inner parts, cork
2 (3-5 mm) and cork 3 (5-8 mm), was shown in Figure 3b,
indicating that the airborne PAH accumulation in the cork
decreases rapidly with the increase in depth. The PAHs
concentrations in tree cortex and phloem are lower than
Tianbao Rock
XMU
R2
slope intercept
41.08 ( 6.67 20.81 ( 3.67
6.52
9.98 0.728
2.72 ( 1.19 3.33 ( 1.18 33.64 -0.95 0.763
5.80 ( 0.72 3.17 ( 0.46 21.91 -3.37 0.934
28.43 ( 4.01 4.13 ( 0.45
5.60 -8.90 0.991
62.39 ( 9.64
3.7 ( 0.53 86.37 -64.48 0.851
5.11 ( 0.34 2.95 ( 0.41 41.17 -4.40 0.855
37.06 ( 4.63 18.89 ( 2.34 111.8 -10.94 0.883
35.57 ( 4.67 27.78 ( 3.65 90.62
1.97 0.889
5.23 ( 0.76 3.56 ( 0.58 21.08 -12.41 0.911
12.05 ( 1.09 7.86 ( 1.01 164.3
-7.34 0.725
6.69 ( 1.01 3.20 ( 0.36 14.73
1.40 0.927
3.63 ( 0.47 3.34 ( 0.38
1.65
3.13 0.887
5.90 ( 0.59 2.94 ( 0.32
8.01
2.78 0.838
6.05 ( 0.67 4.83 ( 0.65
1.30
5.11 0.701
4.90 ( 0.63 4.60 ( 0.50
3.81
3.63 0.867
1.88 ( 0.22 2.02 ( 0.21
2.86
1.68 0.839
those in the cork. This could suggest that only gas-phase
PAHs and a fraction of particle-phase PAHs can be accumulated into inner bark through the lenticels. On the other
hand, the higher concentrations of PAHs in both cork
cambium and vascular cambium, which were 5-8 times
higher than those of the xylem, might be attributed to their
active merism. Compared with the high PAHs concentrations
in the vascular cambium, the low PAHs concentrations in
the xylem indicated that radial diffusion of the PAHs from
the outer tissue to the inner ones is not significant;
furthermore, the lower PAHs concentrations in the xylem as
compared with those in the host soil, ranging from 12.5 ng/g
for Acp to 145 ng/g for FL and Pyr, suggested that tree uptake
of the PAHs deposited in the soil is very limited. This is in
agreement with the hypothesis that the translocation process
from the root depends on water, given the low solubility of
PAH in water. A similar phenomenon for PCBs was observed
by Meredith and Hites (6). Although plants take up significant
quantities of airborne PAHs through accumulation in leaves
(25-29), the PAHs concentration in the phloem found in
this study is not higher than those in the cortex; this is the
evidence that the translocation of the accumulated the PAHs
in leaves via phloem stream did not occur (24).
Mechanism of Airborne PAHs Accumulation in Cork.
The concentrations of 16 EPA PAHs in cork and the
corresponding TSP were listed in Table 1. The correlations
between the concentrations of differently ringed PAHs in
the tree trunk tissues, TSP, and host soil were calculated by
correlation analysis by Origin version 6.0. The correlation
coefficients between the concentration of PAHs in the tissues
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FIGURE 4. Plot of the logarithm of the slope of the cork-TSP PAH regression vs (a) the log Koa of the 16 EPA PAHs and (b) log Vp of PAHs
with log Koa > 8.5.
and TSP were from 0.937 to 0.981, suggesting that airborne
PAHs are the principle source for the accumulation of PAHs
in the tissues, while the correlation coefficients between the
concentrations of PAHs in the tissues and those in the host
soil (ranging from 6.16 ng/g for BghiP to 145.0 ng/g for FL)
were smaller than -0.038, indicating that accumulation of
PAHs from the host soil is very limited.
When the concentration of each PAH in the cork was
plotted against that in the corresponding TSP, a positive linear
relationship was observed, and the slope was listed in Table
1. It reflects the relative accumulation tendency of a certain
airborne PAH on the cork to TSP. The slopes of two, three,
and four ring PAHs are higher than those of PAHs with five
and six rings. This might be attributed to the fact that the
2-4-ring PAHs have a substantial vapor phase in contrast to
the heavier species, which are almost totally bound to
atmospheric particles. This finding is consistent with other
studies suggesting that the long-term PAHs partitioning
process between air and vegetation is primarily governed by
the atmospheric gas-phase PAHs (30-32).
McLachlan reported that plant uptake of semivolatile
organic compounds (SOCs) occurs primarily by one of three
process: equilibrium partition for log Koa < 8.5, kinetically
limited gaseous deposition for 8.5 < log Koa < 11, or particlebound deposition for log Koa > 11 (33). For 16 EPA PAHs,
logarithms of their slopes were plotted against those of their
octanol-air partition coefficients (log Koa), which can be
calculated by the equation Koa ) (RTKow)/H, where Kow is the
partition coefficient between octanol and water; H is Henry’s
law constant (Pa m3/mol); R is the gas constant (8.314 J/mol
K); and T is the absolute temperature (K). A positive linear
relationship (R2 ) 0.796) was observed for the PAHs of log
Koa smaller than 8.5 (Figure 4a). The result implied that the
relative accumulation degree of these PAHs on the cork to
TSP is log Koa dependent. However, the PAHs of log Koa greater
than 8.5 showed a negative linear relationship (R2 ) 0.956)
between the log slope and log Koa, indicating a different
accumulation mechanism for them. Nap and BkF were not
included because of their notable discrepancy. PAHs bound
to the atmospheric particles were governed by their vapor
pressures, and a good regression of R2 ) 0.982 was observed
when the logarithm of vapor pressure (log Vp) was plotted
against the logarithm of the slope (Figure 4b), showing a log
Vp dependent accumulation of these high ringed PAHs on
the cork. The previous results suggested that the accumulation of airborne PAHs by cork occurs in two possible ways:
chemical accumulation on the lipophilic cork cells predominantly for gas-phase PAHs, and physical entrapment by the
lenticels on the surface of the cork mainly for particle-phase
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PAHs. The accumulation degree might be interpreted by Koa
and Vp of PAHs, besides the influences from variable natural
conditions.
Historic Change of Airborne PAHs Pollution Level in
Fujian, Southeastern China. On the basis of the previous
discussions, PAHs in the cork are mainly from airborne PAHs.
The concentrations of 16 EPA PAHs, in all dated corks of the
bark pocket in the Longpetiole Beech tree trunk sampled
from Fujian, southeastern China, were thus employed for
evaluating the historic changes of airborne PAHs levels. The
total concentrations of them were plotted against the time
in Figure 5a, showing that PAHs concentrations progressively
increased from 43.5 ng/g recorded in the earliest available
cork in 1873-1875 to the maximum 345.7 ng/g in 19561961 and then gradually decreased to 267.0 ng/g in 2003.
The historic change of BaP (Figure 5b), which is a typical
known animal and human carcinogen (group IIA) by the
International Agency for Research on Cancer (IARC), is very
similar to that of total 16 EPA PAHs. However, it should be
noted that the accumulated amounts of PAHs on the cork
were influenced by many complex factors such as the
properties of tree species (age, bark surface roughness, and
lipid content), sampling position and depth, as well as
environmental variables (wind direction, atmospheric stability, ambient temperature) (30, 31, 33-36) besides the
atmospheric PAHs concentrations. When the absolute PAHs
concentrations in the dated cork of the bark pocket were
directly utilized to evaluate PAHs pollution levels in the
atmosphere, there must be some uncertainties (37). For
example, the gradual increase of ambient temperature might
be responsible for the decreasing trend of the total concentration of 16 EPA PAHs in the dated corks of the bark pocket
from the middle of 20th century.
Although perylene (PER) has been detected in a number
of anthropogenic sources (biomass burning, gasoline engine
emissions, tire crumb combustion emissions, etc.), only trace
or small amounts of PER are produced during combustion
or by abnormal thermal exposure of organic material as
compared with other unsubstituted PAHs (38). Considerable
evidence has shown that PER may be biologically and
microbially produced under anaerobic conditions (39, 40).
The concentration change profile of PER in the corresponding
dated cork of the bark pocket was also distinct from that of
other PAH determined in this study, slightly fluctuating at
0.178 ( 0.033 ng/g (Figure 5b). It might exist in the
atmosphere through the emission from the natural sources
and be accumulated by tree corks in a similar way. It was
thus used to calculate the concentration ratio of a total of
16 EPA PAHs or BaP to PER for minimizing the influences
FIGURE 5. Historic changes of the absolute concentration and the concentration ratio to PER of (a) total 16 EPA PAHs and (b) BaP, which
were revealed by the Longpetiole Beech (Fagus longipetiolata) bark pocket sampled from Tianbao Rock National Natural Reservation,
southeastern China in July 2003.
by the previously discussed factors. The ratios of the total 16
EPA PAHs to PER and BaP to PER were plotted against the
time in Figure 5, panels a and b, respectively, showing that
from 1873 to 2003, the ratio for PAHs to PER increases from
193 to 2432 and that for BaP to PER from 2.1 to 8.7. From
the Opium War in 1840, the gate of China was gradually
opened. As the progressive industrialization in southern and
southeastern China from the beginning of 20th century and
more and more inherent anthropogenic activities occurred,
the historical increase in atmospheric PAHs input over time
was reflected by the increase in the PAHs concentrations in
the bark pocket shown in Figure 5. Compared with the
absolute PAHs concentrations in the dated corks of the bark
pocket, the concentration ratios of the total 16 EPA PAHs to
PER and/or BaP to PER are more practical in reflecting the
historic change of airborne PAHs pollution levels in the region,
especially from the middle of the 20th century. After New
China was founded in 1949, the industry and economy
explosively developed, several heavy industrial cities were
established, and the population increased sharply in southeastern China. The exponential increase in the concentration
ratio from the 1950s fairly reflected the rapid increase of
airborne PAHs pollution level caused by the increase of
anthropogenic sources of PAHs. Also, the absolute values
(about 45 ng/g) for the total concentration of total 16 EPA
PAHs in the bark pocket are generally invariable from 1873
to 1896, which might be thought of as the natural background
level in the region. Extensive research on the fundamentals
and application of this methodology to the other members
of POPs is underway in our laboratory.
Acknowledgments
This study was partly supported by National Basic Research
Program of China (No. 2003CD415001) and Xiamen municipal Sci. & Technol. Project (No. 3502Z20031058). We thank
Dr. K. Satake and Dr. D. Bellis of National Institute for
Environmental Studies and Dr. K. Tsunoda and Dr. T.
Umemura of Gunma University of Japan for valuable
discussions and partly financial support from Nissan Science
Foundation at the beginning of this research. We also thank
Dr. G. Jiang of Research Center for Eco-environmental
Sciences, the Chinese Academy of Sciences for sincerely
suggestions. The loan of Shimadzu GC-MS QP2010 is much
appreciated.
Supporting Information Available
Figure of correlation between concentrations of different
ringed PAHs. This material is available free of charge via the
Internet at http://pubs.acs.org.
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Received for review February 29, 2004. Revised manuscript
received June 30, 2004. Accepted July 6, 2004.
ES049685J