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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 4740

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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 VOL. 38, NO. 18, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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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 4742

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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