Levels of Extractable Organohalogens in Pine Needles in China

Pine needles can accumulate organohalogens from the ambient air, which are, hence, able to serve as a biomonitor to evaluate the levels of organochlor...
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Research Levels of Extractable Organohalogens in Pine Needles in China DIANDOU XU,† WEIKE ZHONG,† L I N L I N D E N G , ‡ Z H I F A N G C H A I , †,* A N D XUEYING MAO† Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918, Beijing 100039, China, and Environment and Energy Department, Beijing Polytechnic University, Beijing 100022, China

Pine needles can accumulate organohalogens from the ambient air, which are, hence, able to serve as a biomonitor to evaluate the levels of organochlorinated contaminants in the atmospheric environment. Extractable organochlorine (EOCl), the most abundant of the extractable organohalogens (EOX) in environmental samples, has received much attention as a parameter for evaluation of total contamination levels of organochlorinated compounds (OCs). However, few data concerning EOCl in vegetation are available. In this study, we selected pine needles from 17 different areas in China as a sampling matrix to reflect the regional distribution of OCs. EOX (EOX ) EOCl + EOBr + EOI) were measured by instrument neutron activation analysis for their concentrations and distribution in pine needles. The concentrations of EOX were on the order of EOCl . EOBr > EOI. About 5-38% of EOCl remained as sulfuric acidresistant organochlrine (EPOCl). The relatively high concentrations of EPOCl in pine needles from remote areas suggested that EPOCl mainly originated from longrange atmospheric transport and contaminated soil. The relative proportions of the known organochlorines (such as HCHs, DDTs, aldrin, heptachlor, and chlordanes) to total EOCl and EPOCl were 0.3-5.2% and 1.4-19.8%, respectively, which implied that a major portion of the EPOCl measured in pine needles was unknown. The EPOX accumulation rates were preliminarily estimated under the natural condition, which suggested that the “young” needle accumulated EPOX more quickly than the “old” and more than 94% of EPOX was accumulated at the first year of pine needles.

Introduction A huge amount of organochlorinated compounds (OCs) is continuously being released into the environment with the extensive use of organochlorinated pesticides (OCPs) and herbicides and discharge of wastewater from bleaching of pulp and municipal wastewater treatment. Polychlorinated biphenyls (PCBs) and OCPs such as hexachlorocyclohexanes * Corresponding author. Phone: 86-10-88212859. Fax: 86-1088212859. E-mail: [email protected]. † Institute of High Energy Physics. ‡ Beijing Polytechnic University. 10.1021/es025799o CCC: $25.00 Published on Web 11/19/2002

 2003 American Chemical Society

(HCHs), dichlorodiphenyl trichloroethane (DDT), and its metabolites are well known among those OCs for their persistence, toxicity, and bioaccumulation, and these compounds have been widely investigated in foods (1, 2), vegetation (3, 4), and the atmosphere (5, 6). Recently, interest in using extractable organhalogens (EOX) as parameters for the quantification of total organohalogen content in sediment (7), biota (8), and water (9) has dramatically increased. However, there is ever-growing evidence that the known OCs account for only a minor part of the total amount of extractable organochlorinated compounds (EOCl) in biota (10, 11) and sediment (12). From an ecotoxicological point of view, organhalogens, including EOCl, extractable organobrominated (EOBr), and organoiodinated compounds (EOI), may be important to biota and human being because Pellinen and Soimasuo (13) observed that those compounds had a toxic influence on some aquatic biota. Pine needles can accumulate organohalogens from the ambient air and therefore can serve as a biomonitor to monitor the levels of atmospheric contamination of these compounds (14, 15). As an atmospheric biomornitor, pine needle integrates contaminants over a long time, and pine needle samples are much easier to collect than air samples, especially in remote areas. Moreover, pine is widespread in China and its age is easy to determine. Recently, many researchers have used pine needles to quantitatively estimate local and regional atmospheric contamination levels and to identify unknown sources of pollution (16, 17). However, most research was focused on understanding the fate, behavior, distribution, and effects of the known organochlorinated pollutants, such as PCBs, hexachlorobenzene (HCB), and OCPs. Although a significant number of studies have been carried out to determine the EOX concentrations in sediment (18, 19) and biota (20), few data about the total halogens and EOX concentrations in vegetation are available. The need to determine the contents of the total EOX and extractable persistent organohalogens (EPOX) in an atmospheric biomonitor such as pine needles is obvious because they can reflect the actual contamination levels of OCs in the atmosphere. The objective of our work was to study the distribution pattern of total halogen elements and EOX and to investigate the accumulation characteristics of EOCl, EOBr, and EOI in pine needles. To evaluate the contribution of known organochlorine to total EOCl, 11 OCPs, such as HCHs, DDTs, heptachlor, aldrin, and chlordanes, were also determined. In addition, to get some idea about what percentage of the EOCl in pine needle extract can be expected to be persistent, the extracts were treated with concentrated sulfuric acid according to the methods reported by Martinsen (9) and the sulfuric acid-resistant EPOCl was determined. Some environmental impact factors, e.g., temperature and precipitation, upon the accumulation degree of OCs in pine needles were also estimated based on the records of local meteorological observatory stations in sampling sites.

Experimental Section Sample Collection. Pinus massoniana Lamb. and Pinus tabulaeformis Carr. needles were collected at 17 remote areas in China (Figure 1) in 2001. The sampling locations were 15 km or more from major urban centers and at least 1.0 km or more from highways and not influenced by obvious pollution sources (e.g., hydroelectric transformer, waste sites, and factories). Pine needles were collected at least from five VOL. 37, NO. 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Map of sampling in China. individual trees at heights of 1.5-3 m at each sampling point. Sampling was mostly done from April to May 2001. Ten samples from Guiyang and Guilin were collected in November 2001. In January 2002, pine needles of known age observed by their position on branches in the Beijing area were collected for estimation of the accumulation rates (AR) of organohalogen. Needle samples with different ages were taken from the same branches so that the environmental effects on them were same. The ages were 0.75 and 1.75 years for the P. tabulaeformis Carr. needles since their buds generally started to shoot in early April in Beijing. In the meantime, the records of the local meteorological observatory stations were also collected. Pine needles were placed in polyethylene bags immediately after sampling, and then some samples were used to analyze water content; the rest was dried at room temperature and stored in polyethylene bags at room temperature in the dark until analysis. Chemicals. Pesticide reference standards R-, β-, γ-, and δ-HCH, heptachlor, aldrin, cis-chlordane, trans-chlordane, p,p′-DDE, p,p′-DDD, and p,p′-DDT were purchased from Sulpelco. The working standard solutions were prepared by dissolving the appropriate amount of OCPs in distilled cyclohexane. The acetone and cyclohexane were redistilled before use. The laboratory glassware was washed with acid and detergents, rinsed with distilled water and acetone, and then heated to 200 °C overnight prior to use. Extraction and Cleanup. The cellulose thimble for extraction was pre-extracted successively with acetone and cyclohexane and dried in an oven (100 °C, 6 h) before use. A total of 4-7-g pine needle samples were minced, homogenized, and Soxhlet-extracted with a mixture of cyclohexane and acetone (1:1, 250 mL) for 16 h. To obtain more information from a sample, four analyses were performed for each sample, first for total halogens, second for EOX, then for EPOX, and finally for OCPs. Ten milliliters of the crude extract was taken for lipid determination by gravimetric analysis. The remaining crude extract was washed three times with 2% sodium sulfate to remove acetone. The aqueous phases were again extracted with 30 mL of fresh cyclohexane, and the organic phases were incorporated. A 20-mL aliquot of extract was taken for determination of EOCl, EOBr, and EOI after washing three times with 20 mL of distilled water, followed by drying with anhydrous sodium sulfate, and concentration to 2-4 mL by rotary evaporation. To measure the EPOCl, EPOBr, EPOI, and the OCPs, the remaining extracts were treated repetitively with concentrated sulfuric acid until a clear and colorless cyclohexane extract was obtained, followed by washing three times with 100 mL of distilled water, drying with anhydrous sodium sulfate, and concentrating to 2-4 mL by rotary evaporation. 2

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Analysis. The water content of the pine needles was determined to be about 56-66% weight by drying (120 °C) them to constant weight. For the lipid analysis, a watch glass was heated to 250 °C overnight and stored in a freeze-dryer until the weight was constant. Aliqouts (10 mL) if the crude extracts were put into the watch glass and were then lyophilized until constant weight. In this way, loss of the volatile compounds was minimized. The relative standard deviation (RSD) of five analyses was (6%. The concentrations of total halogens in pine needle samples were determined by instrumental neutron activation analysis (INAA) according to the method reported by Hou et al. (21). An aliquot of ∼1.2 mL of the extract for EOX or EPOX analysis was heat-sealed in a 1.5-mL acid-washed polyethylene vial. The vial was washed with distilled water and acetone after an acid rinse, stored in cyclohexane overnight, and dried in an oven at 50 °C. Potassium chloride, potassium bromide, and potassium iodate of known concentrations, dissolved in distilled water, were used as standards. The concentrations of standards were 1.0, 1.0, and 0.7 µg/mL for Cl, Br, and I, respectively. INAA was carried out at a neutron flux of 8.0 × 1011 n/cm2‚s for 15-min irradiation using a miniature neutron source reactor at the Institute of Atomic Energy (IAE), Beijing, China. To minimize the radioactivity background, the samples were transferred to a new counting vial after irradiation. The γ-energy spectra were detected with a high pure germanium detector with associated electronics interfaced to a computer-controlled EG&G Ortec multichannel analyzer for peak area calculations. The analyses were based on γ-peaks from 38Cl (t1/2 ) 37.24 min, Eγ ) 1642 keV), 80Br (t1/2 ) 17.68 min, Eγ ) 617 keV), and 128I (t1/2 ) 24.99 min, Eγ ) 443 keV). The counting time was 15 min. The detection limits were 50, 8, and 3.5 ng for Cl, Br, and I, respectively. The gas chromatography analyses were carried out by a Varian 3800 gas chromatograph equipped with a 63Ni electron capture detector, using a fused-silica capillary column (CPSil 8 CB 50 m × 0.25 mm i.d., with 0.12-µm film thickness). The temperature settings for the injection and detector were 250 and 300 °C, respectively. An initial column temperature of 130 °C was held for 5 min, then programmed at 20 °C/min to 220 °C and 4°C/min to 270 °C, and held at 270 °C for 10 min. Oxygen-free nitrogen (99.999%) was used as carrier and makeup gas. Analytical Quality Assurance. Twenty percent of the samples were extracted and analyzed as duplicates. The relative standard deviations of three analyses were 11% for EOCl, 16% for EOBr, and 14% for EOI. The total blank values of the analytical procedure were determined by extracting a cellulose thimble by the same method as the real samples. The blank values of Cl, Br, and I were subtracted to correct the experimental values. 24Na (t1/2 ) 15.0 h, Eγ ) 2754 keV) was simultaneously determined as a check for contamination caused by inorganic halogens (22). The results indicated that 24Na was not found in the sample and blank extracts, which meant that the contamination from inorganic halogens was negligible. A 250-mL aliquot of cyclohexane/acetone (1:1) was concentrated to 0.2 mL and used to check the contamination from the solvent. No significant peaks overlapping OCPs standards should appear in the chromatogram of the blank. GC peak identification was conducted by comparing gas chromatographic retention time with that of an authentic standard. Generally, the column cleanup procedure was necessary after treatment with concentration sulfuric acid, but there were no obvious peaks interfering with the quantification of OCPs. Thus, the cleanup step was omitted to reduce loss of the analytes. Each analysis was performed in duplicate or triplicate, and the chemical recoveries of the

TABLE 1. Concentrations (µg/g) of EOX and EPOX in Pine Needles from China no.

location

lipid (%)

EOCl

EOBr

EOI

EPOCl

EPOBr

EPOI

total Cl

total Br

total I

1 2 3 4 5 6 7 8 9 10. 11 12 13 14 15 16 17

Xi Baipo (XB)a Taishan (TS) Zaozhuang (ZZ) Xuzhou (XZ) Nanjing (NJ) Suzhou (SZ) Hangzhou (HZ) Jinhua (JH) Lushan (LS) Meiling (ML) Shaxian (SX) Xiamen (XM) Nanxiong (NX) Guilin (GL) Fengjie (FJ) Qijiang (QJ) Guiyang (GY)

9.8 5.8 6.9 7.4 5.4 4.2 5.7 11.4 5.7 4.2 6.9 9.7 3.1 nad na 3.4 5.8

3.2b (33)c 2.9 (50) 4.0 (58) 6.0 (81) 2.4 (44) 2.7 (64) 4.0 (70) 2.4 (21) 3.6 (63) 5.2(124) 1.6(23) 2.6 (27) 0.5(16) na na 5.2(153) 3.6(62)

0.06 (0.6) 0.2 (3.4) 0.3 (4.3) 0.54 (7.3) 0.13 (2.4) 0.2 (4.8) 0.11 (1.9) 0.20 (1.8) 0.26 (4.6) 0.25(6.0) 0.072(1.0) 0.08 (0.8) 0.06(1.9) na na 0.23(6.8) 0.07(1.2)

0.04 (0.4) 0.2 (3.4) 0.2 (2.9) 0.4(5.4) 0.11 (2.0) 0.15 (3.6) 0.06 (1.1) 0.05 (0.4) 0.07 (1.2) 0.08(1.9) 0.03 (0.4) 0.03(0.3) 0.013(0.4) na na 0.11 (3.2) 0.07(1.2)

1.2(12) 1.1(19) 1.5(22) 1.4(19) 0.63(12) 0.74(18) 0.68(12) 0.9(8) 0.45(8) 0.31(7) 0.34(5) 0.7(7) 0.13(4) 0.67 2.6 0.27(8) 0.24(4)

0.019(0.2) 0.13(2.2) 0.14(2.0) 0.13(1.8) 0.061(1.1) 0.12(2.9) 0.052(0.9) 0.1(0.9) 0.09(1.6) 0.086(2.0) 0.07(1.0) 0.07(0.7) 0.036(1.2) 0.0067 0.051 0.024(0.7) 0.016(0.3)

0.014(0.1) 0.1(1.7) 0.1(1.4) 0.095(1.3) 0.06(1.1) 0.09(2.1) 0.005(0.09) 0.03(0.3) 0.042(0.7) 0.016(0.4) 0.02(0.3) 0.01(0.1) 0.011(0.4) I, which was in agreement with their element abundance in nature. EOCl and EPOCl accounted for 0.1-3.9% and 0.02-0.3% of the total chlorine, which suggested that chlorine in pine needles mainly exists as inorganic species and nonextractible organochlorinated compounds. Respectively, 0.2-15% and 0.09-4.8% of the total bromine were EOBr and EPOBr, while EOI and EPOI were 2-57% and 0.8-25% of the total iodine, which suggested that the relative proportions of EOBr and EOI were much higher than those of EOCl in the total content. Extractable Organohalogens. The concentrations of organohalogens were in the order of EOCl . EOBr > EOI

(Table 1). EOCl accounted for 86-97% of EOX in all the pine needle samples (Figure 2), which showed that EOCl was the major fraction of the organohalogens. Similar results have been reported by Christina and co-workers (23) and Kannan et al. (24) for aqueous biota. The different distribution of the organohalogens is likely attributed to two factors: (1) Most organohalogenated pollutants in the atmosphere are present as OCs, which can be taken up by pine needles. Laniewski and co-workers (25) found that most absorbable organohalogens in rain and snow were OCs. Yokouchi (26) provided further evidence that chlorinated methane originating from both natural and antropogentic sources was the most abundant organohalogen in the atmosphere and was continuously released in large quantities into atmosphere from coastal land. Robert and co-workers (27) also found that there was a huge amount of natural brominated methane and chlorinated methane were released to atmosphere from coastal salt marsh with an average molar flux ratio of rough 1:20. (2) OCs may be more difficult to be transformed and degraded than organobrominated and-iodinated compounds in the environment. The highest concentration of EOCl was in Xuzhou (6.0 µg/g, dry weight), followed by Meiling and Qijiang, which were ∼10-12-fold higher than the lowest concentration (0.5 µg/g, dry weight) in Nanxiong. The known organochlorines such as HCHs (R-, β-, γ-, and δ-HCH), DDTs (p,p′-DDT, p,p′DDE, p,p′-DDD), heptachlor, aldrin, and chlordanes (cis- and VOL. 37, NO. 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Relationship of EOCl and EOBr or EOI, EOBr to EOI, and EPOBr to EPOI in pine needles. trans-chlordane) accounted for 0.3-5.2% of EOCl in pine needles, suggesting the presence of a considerable amount of other unknown organochlorines. The previous report also showed that the known organochlorinated pollutants contributed to less than 10-15% of the EOCl in fish and ∼5% in sediments from Bornholm in the Baltic Proper (28). In fish and sediment, ∼60-80% of EOCl can be hydrolyzed by lipase, and ∼30% of EOCl were acidic material (28). Lunde and Steinnes (29) showed that a fair amount of EOCl in marine organism oil was synthesized by natural processes in the marine environment. Grimvall (30) found that the major part of the organohalogens in freshwater and the marine environment came from the natural incorporation of halogens into humic substances or other macromolecules. However, Kiceniuk and co-workers (31) found that it was impossible to account for the observed high levels of EOCl in tissues of beluga whales from natural compounds. However, few data about EOCl in vegetation are available for comparison. Further studies are needed to better understand the unknown EOCl. The concentrations of EOBr ranged from 0.6 to 7.3 µg/g, lipid weight. EOI concentrations were comparable to EOBr in most samples, which ranged from 0.3 to 5.4 µg/g, lipid weight. No correlation between the concentrations of EOCl and EOBr or EOI (Figure 3a and b) demonstrates that their sources are different. However, there is a correlation between the concentrations of EOBr and EOI and the similar pattern for EPOBr and EPOI (Figure 3c and d), which shows that EOBr and EOI in pine needles might come mainly from natural source. In marine fish, EOBr was similar to triacylglycerols and sterol esters (32). Tinsley and Lowry (33) also found that 60-80% of the organobrominated compounds were associated with brominated fatty acids. However, few data are available for EOBr species in vegetation. Further studies are needed to identify the organobromine species in vegetation. Extractable Sulfuric Acid-Resistant Organohalogens. About 5-38% of EOCl survived as the species of EPOCl (sulfuric acid-resistant) after treatment with concentrated sulfuric acid, which suggested that >62% of EOCl in pine needles was an acid-liable or acid-soluble fraction. Most compounds with heteroatoms (oxygen or nitrogen atom) or an unsaturated bond, such as most known naturally occurring organochlorinated compounds, can be protonated or destroyed and removed from the extracts after treatment with concentrated sulfuric acid (34, 35). Thus, a conclusion can be drawn that the natural EPOCl cannot be neglected, but its contribution is probably limited in comparison with that from the ambient air. The occurrence of rather high EPOCl in the samples collected from the remote sites, far from anthropogenic pollution sources, suggested that it resulted 4

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FIGURE 4. Variation trends of OCPs and EPOCl concentrations. from long-range atmospheric transport and local contaminated soil. Earlier research showed that soil was an important pollutant sink and volatilization was a major loss mechanism of organochlorinated pollutants (36). Bacci and Gaggi (37) and Travis and Hattemer-Frey (38) also showed that soilair-foliage is an important route for hydrophobic chemicals in soil. The concentrations of EPOX were also in the order of EPOCl . EPOBr > EPOI. About 73-97% of EPOX was accounted for as EPOCl. The concentrations of EPOCl ranged from 0.13 to 2.6 µg/g, dry weight, in pine needles, which were comparable to the concentration range of 0.27-1.4 µg/ g, dry weight, in mosses from the Ling Mountain and Wuling Mountain near Beijing (39). They were the highest in Fengjie, followed by Zaozhuang and Xuzhou, and the lowest in the Nanxiong samples, being consistent with the trend of EOCl, which suggested that the environmental contamination level of OCs in Nanxiong either was very low or had to be related to the lowest lipid content. Many controlled experiments and field experiments have shown that the lipid concentration of leaf would influence the degree of lipophilic pollutant accumulation from air to leaf (40-42). On a dry weight basis, it is found that the concentrations of EPOCl noticeably increased from south to north China, which is consistent with the trend of the concentrations of OCPs (Figure 4). EPOBr and EPOI are also found to show the same spatial trends. The results indicated that the OCs contamination levels were more serious in north China than in south China. In the meantime, it might be related to the difference in environmental conditions, e.g., temperature, precipitation, and other factors (see Environmental Factors section). The concentrations of the known, i.e., identified, organochlorines such as HCHs, DDTs, and chlordanes in pine needles are listed in Table 2. The known organochlorines

TABLE 2. Concentrations of the Known Organochlorines in Pine Needles Collected from China (ng/g, Dry Weight) location Xi Baipo (XB) Taishan (TS) Zaozhuang (ZZ) Xuzhou (XZ) Nanjing (NJ) Suzhou (SZ) Hangzhou (HZ) Jinhua (JH) Lushan (LS) Meiling (ML) Shaxian (SX) Xiamen (XM) Fengjie (FJ) Qijiang (QJ) Guiyang (GY) Guilin (GL) Nanxiong (NX)

43.5 27.7 32.4 29.1 9.9 34.6 17.1 39.0 17.7 11.2 23.5 19.2 24.8 12.6 16.9 62.7 15.1

1.7 1.6 5.0 5.0 2.0 1.5 1.6 4.0 1.6 2.6 6.1 8.1 3.3 2.1 12.1 4.4 3.9

0.5 1.7 5.5 4.2 18.5 2.9 13.0 4.2 1.5 1.5 1.8 2.1 7.3 8.7 2.3 57 6.8

0.7 0.9 4.9 6.0 1.1 2.5 1.2 2.2 0.7 1.7 3.2 1.4 2.1 1.4 3.0 6.7 nd

nd 46.4 0.6 32.5 1.7 49.5 1.3 45.6 ndd 31.5 nd 41.5 nd 32.9 1.3 50.7 nd 21.5 nd 17 nd 34.6 0.6 31.4 nd 37.5 nd 24.8 nd 34.3 nd 130.8 nd 25.8

HCHs)R + β + γ + δ isomers. DDTs)DDT + DDE + DDD. Chlordans) cis-hlordan + trans-chlordan. d nd, not detected. a

c

HCHsa DDTsb heptachlor chlordansc aldrin total Cl

b

FIGURE 5. Relative contribution (%) of identified and unidentified organochlorine to EPOCl. accounted for 1.4-19.8% of EPOCl in pine needles, which implied that the relative proportions of the known to unknown organochlorine were very low (Figure 5). But there was a relative enrichment of these OCPs in EPOCl compared with in EOCl by a factor of 3 to 20. The known compounds were reported to account for 5-25% of EOCl in fish from the United States (24) and 2-18% in marine organisms from the Osaka Bay (43). About 45% of EOCl reported in blubber lipid of beluga whales are attributed to the known compounds (31). A total of 25-50% of EOCl in herring gull eggs from the Lake Ontario can be explained by the known compounds (44). The identified compounds in birds from Georgia (USA) accounted for 1-14% of EOCl (24). In Japanese human adipose, ∼59% of EOCl can be accounted by PCBs, DDTs, PCTs, and HCHs (43). In contrast with the above results, the relative proportions of the unknown EOCl in pine needles are higher than those found in aqueous and terrestrial biota. The concentration ranges of EPOBr and EPOI were 0.0067-0.14 and 0.005-0.1 µg/g, dry weight, respectively (Table 1), which were higher than those found in mosses (EPOBr, 0.001-0.018 µg/g dry weight; EPOI, 0.0005-0.004 µg/g dry weight) collected from the Ling Mountain and Wuling Mountain (39). Few data about the concentration of total organohalogenated compounds in terrestrial plants are available in the literature. Therefore, it is impossible to compare our results with others. On a lipid basis, the

FIGURE 6. Variation trends of Kimp and EPOCl concentrations with the sampling locations. concentrations of EPOBr are 6-32 µg/g in blue mussel (7), much higher than those found in pine needles (0.6-7.4 µg/ g). It is similar for EOBr that its concentrations are 43-210 µg/g, lipid weight, in blue mussel (7) and 4-33.6 µg/g, lipid weight, in terrapin (24), much higher than those in pine needles. Aqueous biota contain higher concentrations of EOBr and EPOBr than plant, partly because organobrominated compounds can be biosynthesized and concentrated in food chains (28, 44, 45). Environmental Factors. Environmental factors, such as temperature, precipitation, and concentration of lipophilic pollutants in air, play an important role in the accumulation process of lipophilic pollutants such as most persistent OCs since the main accumulation pathway for these compounds is from air to leaf. Generally, the appropriate temperature increase would have a positive effect on accumulation of most lipophilic pollutants. Many studies have shown that Koa (octanol-water partition coefficient) is a good predictor of lipophilic pollutant accumulation in leaves and generally gas-phase pollutants with a large Koa are preferentially accumulated (42, 46, 47). Harner and Mackay stated that Koa is strongly dependent on temperature and simultaneously pointed out that Koa increases by a factor of ∼30 from -10 to +20 °C (48). Hoff and co-workers (49) also found that the concentrations of PCBs, PCC, and OCPs in the atmosphere in summer is much higher than that in winter. However, precipitation can scavenge the OCs in the atmosphere and decrease the concentrations of OCs in air. Considering both factors, temperature and precipitation, an environmental impact factor Kimp can be defined as

Kimp ) T/R

(1)

where T (°C) is the annual average temperature at the sampling site and R (mm) is the annual average rainfall. Figure 6 showed that the variation trend of Kimp was almost consistent with the concentrations variation of EPOCl, which strongly indicated that the environmental factors had a heavy influence on EPOCl accumulation in pine needles and simultaneously provided further evidence that EPOCl in pine needles mainly originated from the ambient atmosphere. Generally, the accumulation of lipophilic pollutants in plants will be influenced by environmental factors (temperature, precipitation, wind direction and speed), the physicochemical behavior of pollutants, and lipid concentration and surface area of leaf. However, the mechanism of most influence for native plant accumulation under natural conditions is still obscure. This model attempted to estimate the influence Accumulation Rates of EPOX. The average accumulation rates (AR) of EPOCl, EPOBr, and EPOI were calculated based on the measurement results of these three classes of VOL. 37, NO. 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 3. Accumulation Rates (ng g-1 Month-1, Wet Weight) of EPOX in Pine Needles Collected from Beijing accumulation rate

a

compound

1.75 yeara

0.75 yeara

EPOCl EPOBr EPOI

26 4.6 0.95

57 10 2.2

The age of pine needle.

organohalogens in pine needles of different ages under the natural conditions (Table 3). The AR was expressed as

AR ) Ct/t

(2)

where Ct is the average concentration of EPOX in pine needles at age t (months). The AR of EPOCl in the “young” and “old” pine needles were 57 and 26 ng g-1 month-1 wet weight, respectively, which suggested that the EPOCl AR of the “young” needles was quicker than that of the “old” by a factor of 2. About >94% of EPOX were accumulated in the first year of growth of the pine needles. Similar results were obtained for EPOBr and EPOI. Simonich and Hites also found that new vegetation accumulated PAH quickly (42). Clearly, this is a rough estimation because the AR depends on the components of the unknown EPOX, physicochemical characteristics and atmospheric concentrations of these compounds, lipid concentration and surface areas of pine needles, exposure time, and some environmental factors. Thus, more studies are required.

Acknowledgments This work is funded by National Natural Science Foundation of China (Grants 19935020 and 10175075), Chinese Academy of Sciences (Grant KJCX-N01), Foundation of Laboratory of Nuclear Analytical Techniques (Grant K-102), and International Atomic Energy Agency (11921/RBF).

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Received for review May 17, 2002. Revised manuscript received August 2, 2002. Accepted October 8, 2002. ES025799O