°“√»÷°…“ª√‘¡“≥ “√ª√–°Õ∫‚æ≈’‰´§≈‘°Õ–‚√¡“µ‘°‰Œ‚¥√§“√å∫Õπ „π∫√√¬“°“»„π‡¢µÕÿµ “À°√√¡·≈–‡¢µ‡¡◊Õß Investigation of PAHs in Ambient Air in Industrial and Urban Area Wanna Laowagul*, Phaka Sukasem*, Sunthorn Ngodngam*, Monthip Srirattana Tabucanon*
°“√»÷ ° …“¡≈¿“«–∑“ßÕ“°“»Õ— π ‡π◊Ë Õ ß¡“ ®“° “√æ‘…™π‘¥‚æ≈’ ‰´§≈‘°Õ‚√¡“µ‘°‰Œ‚¥√§“√å∫Õπ (PAHs) ‰¥â°”Àπ¥‡¢µ°“√»÷°…“„πæ◊Èπ∑’Ë°√ÿß‡∑æ¡À“π§√ ·≈–π‘§¡Õÿµ “À°√√¡¡“∫µ“æÿ¥ µ—«Õ¬à“ß PAHs „πΩÿÉπ≈–ÕÕß·≈–„π ¿“«–¢Õß°ä“´∂Ÿ°‡°Á∫Õ¬Ÿà „π°√–¥“…°√Õß™π‘¥ T60A20 ·≈– “√ XAD-2 µ“¡≈”¥— ∫ ∑”°“√∑¥ Õ∫À“ª√‘ ¡ “≥§«“¡‡¢â ¡ ¢â π ¢Õß PAHs ®”π«π 14 ™π‘¥ ‚¥¬„™â‡§√◊ËÕß HPLC ®“°°“√»÷°…“æ∫«à“ 70-80 ‡ªÕ√å‡´Áπµå ¢Õß “√ PAHs ∑’Ë»÷°…“®–Õ¬Ÿà „πΩÿÉπ≈–ÕÕß¢π“¥∑’Ë‡≈Á°°«à“ 2.1 ‰¡§√Õπ ·≈–æ∫‡ªÕ√å ‡ ´Á π µå ¡ “°∑’Ë ÿ ¥ „πΩÿÉ π ¢π“¥ ‡≈Á°°«à“ 0.43 ‰¡§√Õπ≈ß‰ª §à“§«“¡‡¢â¡¢âπ√«¡¢Õß √–¥— ∫ PAHs „π∫√√¬“°“»„π‡¢µ‡¡◊ Õ ß·≈– Õÿµ “À°√√¡‡∑à“°—∫ 12.64 ·≈– 4.69 π“‚π°√—¡µàÕ ≈Ÿ°∫“»°å‡¡µ√ µ“¡≈”¥—∫ ´÷Ëß®–æ∫«à“„π‡¢µ‡¡◊Õß¡’ PAHs √«¡ Ÿß°«à“‡¢µÕÿµ “À°√√¡∂÷ß “¡‡∑à“ Õ¬à“ß‰√
*»Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡ ‡∑§‚π∏“π’ µ.§≈ÕßÀâ“ Õ.§≈ÕßÀ≈«ß ®.ª∑ÿ¡∏“π’ 12120 ‚∑√. 0-2577-1136 ‚∑√ “√. 0-2577-1138 Environmental Research and Training Center, Department of Environmental Quality Promotion. Technopolis. Klong 5 Klong Luang, Pathumthani 12120 e-mail: Wanna@deqp.go.th
°Áµ“¡ §«“¡‡¢â¡¢âπ¢Õß “√ª√–°Õ∫ PAHs ·µà≈–µ—« „π‡¢µ‡¡◊ Õ ß ‡¢µÕÿ µ “À°√√¡·≈–‡¢µ™π∫∑®–¡’ —¥ à«π¢Õß°“√°√–®“¬µ—«Õ¬Ÿà„π√Ÿª·∫∫‡¥’¬«°—π ®“° °“√»÷°…“°“√°√–®“¬¢Õß PAHs „π ∂“π–¢Õß·¢Áß „π√Ÿ ª ¢ÕßΩÿÉ π ≈–ÕÕß ·≈– ∂“π–°ä “ ´ æ∫«à “ 99 ‡ªÕ√å‡´Áπµå ¢Õß PAHs ∑’Ë¡’«ß·À«π 2-3 «ß ®–Õ¬Ÿà „π ∂“π–°ä“´ ·≈–¡“°°«à“ 90 ‡ªÕ√å‡´Áπµå ¢Õß PAHs ∑’Ë¡’«ß·À«π 5-7 «ß ®–Õ¬Ÿà„π ∂“π–¢Õß·¢Áß „π√Ÿª¢ÕßΩÿÉπ≈–ÕÕß à«π PAHs ∑’Ë¡’«ß·À«π 4-5 «ß ®–Õ¬Ÿà„π∑—Èß Õß ∂“π–
ABSTRACT The investigation of polycyclic aromatic hydrocarbon (PAHs) associated with different particle size and gaseous phase were carried out in urban and industrial areas of Thailand. Particulate PAHs were collected on T60A20 Teflon coated glass fiber filter and gaseous PAHs were trapped on XAD-2 adsorbent by using the Andersen Low Volume Air Sampler with an nine stage impactor equipped with a glass tube containing 2 layer of XAD-2 adsorbent. Fourteen PAHs were analyzed by HPLC with fluorescence detector. In both urban and industrial areas, most of PAHs target compounds appear predominantly associated with fine particle size 2.1 µm to less than 0.43 µm of approximately 70-80% and the most abundant concentration was found at the size < 0.43 µm. The total PAHs concentration in urban and industrial areas were 12.64 and 4.69 ng/m3, respectively. The details of their distribution associated with particle size is discussed in this report. The concentration of individual PAHs in total particle and gaseous phase at urban, industrial and rural site are shown in the same pattern. The total PAH concentration was found highest in urban area. The study of gas-particle distribution show that 99% of PAH with 2 to 3 rings exist in the gas phase, and more than 90% of PAH with 5 to 7 rings (high molecular weight) exist in the particulate phase, while PAHs with 4 to 5 rings (low molecular weight) exist in both phases. »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡
1. Introduction Polycyclic Aromatic Hydrocarbons (PAHs) are toxic compounds composed of two or more fused benzene rings. They occur ubiquitously as byproducts of incomplete combustion. PAHs are distributed in the environment via natural combustion (e.g., volcanic eruptions, forest burning) and by anthropogenic combustion processes.1 PAHs from anthropogenic sources with the majority emitted from heat and power generation, (e.g., coal, gas, wood, oil etc.), industrial processes, refuse burning, automobile emissions and other sources such as cooking, smoking and others. They are possibly exposed to human as part of everyday living. Human exposure to PAHs may occur through food, water, air and direct inhalation of tobacco smoke or direct contact with materials containing PAHs. PAHs are considered as potential human health hazard since some of them can cause carcinogenesis, localized skin effects, pulmonary and respiratory problems, genetic reproductive and developmental effect, behavioral, neurotoxic, and other organ system effect. 2 The United States Environmental Protection Agency (U.S.EPA.) has identified 16 unsubstituted PAHs as priority pollutants, eight of which are typically considered possible or probable carcinogens: benzo (a)anthracence, chrysene, benzo (b) fluoranthene, benzo (k) fluoranthene, benzo (a) pyrene, indeno (1,2,3-cd) pyrene, dibenzo (a,h) anthracene and benzo (g,h,i) perylene.3 PAHs can be released to the atmosphere in two forms : absorbed on suspended particles and in gas phase. Since 70-90% of PAHs are found on particles in the range of less than 5 µm4,5 hence they are closely related to the respirable function. Thus, the risk of exposure to carcinogenic materials associated with particulate matter by urban inhabitants (e.g. lung cancer) may be high.
Since the industrial development and urbanization in Thailand have rapidly undergone over the last decade, it is expected that the concentration of PAHs in airborne particulate will be high. Moreover the statistic on cancer in Thailand during 1988-1991 has shown that lung cancer is the most common malignancy of both sexes in areas where air pollution concentration is high. Therefore, it is important to investigate the PAHs concentration in the atmosphere especially in urban and industrial areas in order to assess the PAHs level and to understand the characteristic of PAHs in those areas. The scope of this study was to determine PAHs in suspended particle with regards to size from less than 0.43 µm to more than 11 µm and in gas phase in the ambient air. The samples were taken from three different areas : one sampling site in Bangkok area, as an urban site, four sampling sites in Maptaput Industrial Estate and one sampling site at Environmental Research and Training Centre as a background area. Fourteen PAHs, pyrene (PYR), benzo (a) anthracene (BaA), benzo (e) pyrene (BeP), dibenzo(a,c)anthracene (DBacA), benzo(k) fluoranthene (BkF), benzo (a) pyrene (BaP), dibenzo(a,h)anthracene (DBahA), benzo (g,h,i) perylene (BghiP), 3-methylcholanthrene (3MC), napthalene (NAP), anthracene (ANT), fluoranthene (FLA), indeno(1,2,3,-cd)pyrene (IP) and coronene (COR) were selected as target PAHs in consideration of carcinogenicity and prevalence in the atmosphere.
2. Materials and Method 2.1 Apparatus and Materials PAHs samples were taken in the form of particulate and gaseous phases. Particulate PAHs was collected on T60A20 Teflon coated glass fiber filter by using Andersen Low Volume Air Sampler with an nine stage impactor at §-18
the flow rate of 28.3 l/min for 24 hours at each sampling site. The different size of particles were collected on the filter at the respective stage; the ranges of the particle sizes were >11.0 µm, 11-7.0 µm, 7.0-4.7 µm, 4.7-3.3 µm, 3.3-2.1 µm, 2.1-1.1 µm, 1.1-0.65 µm, 0.65-0.43 µm and <0.43 µm for stages one through nine. Gaseous PAHs was collected by adsorbent tube containing 2 layers of XAD-2 resin, 12.0 g and 5.0 g, respectively, attached to the Air Sampler. High Performance Liquid Chromatography (HPLC), Shimadzu, using acetonitrile and water as mobile phase; a helium degassing unit (Shimadzu, DGU-2A); a mixer; a high pressure pump (Shimadzu LC-9A); a column oven (Shimadzu CTO-6A); and injector valve with an optional 50 µl loop injector; a guard column (Wakosil II 5C 18 AR 4.6 mm I.D. x 30 mm); a main column (Wakosil II 5C 18 AR 4.6 mm I.D x 250 mm); a fluorescence HPLC monitor (Shimadzu RF 535 and Shimadzu RF 551) and chromatopac (Shimadzu CR 7 Ae plus) were used for sample analysis. Standard PAHs were obtained from GL science Inc, Japan. All glassware were cleaned with detergent and washed with tap water then rinsed three times with deionized water. Finally they were rinsed again with methanol, acetonitrile and dichloromethane prior to use.
2.2 Study Area Urban Area : The sampling site is located on the rooftop of the Office of the Environmental Policy and Planning (OEPP) building at 20 meters height. This office is far from the center of Bangkok at approximately 3 km. This site is surrounded by commercial buildings, government offices, houses, roads and expressway. There are two main roads in the vicinity of the site. Rama VI road at 500 m. west side with traffic volume of about 57,000 vehicles/day and Phaholyothin
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road at 500 m. east side with traffic volume of about 63,000 vehicles/day. Both roads are mainly composed by personal and light duty cars and buses. A 24-hours sample was collected for seven days during December 10-16, 1997. Industrial Area : Maptaput Industrial Estate (MIE) was selected as a representative of industrial area. It is located 15 km. western of Rayong province which is far from Bangkok about 208 km. About 50 heavy industries were constructed in this area, mainly petrochemical industries. There are 4 sampling sites in Maptaput Industrial Estate. Three samplers were placed on the rooftop of the building approximately 15 meters height and one sampling was placed on the rooftop of the building approximately 5 meters height. Samples were collected 3 days for 24 hours from each sampling site during January 27-February 1, 1998. Rural Area : Environmental Research and Training Centre (ERTC) is selected as a background area. It is located in a suburb about 50 km. far from downtown of Bangkok. The site is surrounded by houses, roads and paddy fields. The main road in the vicinity of the site is composed by personal and light duty cars and small trucks. The sampler was placed on the rooftop of ERTC building about 15 meters height. Sampling was done 7 days for 24 hours during December 18-25, 1997.
2.3 Sample Analysis The reference analytical method in this study is a highly sensitive analytical method for PAHs developed by Matsushita et al. (1994). The filter samples were extracted with 15 ml. of dichloromethane by ultrasonication for 20 minutes twice at 4-10 ÌC. Let the solution stand for over 30 minutes and transfer 10.0 ml. of the supernatant into a test tube. Pipet 50 µl of dimethysulfoxide (DMSO) »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡
to the extract as a PAHs keeping reagent prior to the evaporation step which were done under a gentle nitrogen blowing. The residues were then dissolved in the test tube with 950 ml of acetonitrile. In a similar way, the similar extraction procedure have been be applied to XAD-2 samples. The extracted sample was cleaned up by filtration using CAMEO II nylon pore size 0.22 µm. The final sample were stored at -86 Ì C deep freezer until analysis will be performed. PAHs were quantified by using a Shimadzu HPLC coupled by a fluorescence detector. Acetonitrile and water were used as the mobile phase which was deoxygenated by bubbling helium through the solvent during the measurement. The flow rate for the mobile phase was 1.0 ml/min. The PAHs compounds were separated by octadecylsilane-bonded C18 (reversed phase column). The selected PAHs in this study were divided into 2 groups; PYR, BaA, BeP, DBacA, BkF, BaP, DBahA, BghiP and 3MC were detected by fluorescence detector at fixed wavelength; excitation wavelength at 290 nm. and emission wavelength at 405 nm. The other groups; NAP, ANT, FAL, IP and COR were detected by scanning fluorescence detector of which excitation and emission wavelengths were automatically set by a time program to detect each PAHs selectively and sensitively. To get a reliable data, the quality assurance procedure was performed. The Certified Reference Material (CRM) 1649 urban dust/organics, repeatability and reproducibility were tested. The result of PAHs analysis on CRM 1649 (urban dust) were in good agreement with the certified value as shown in Table 1 and on average 90% of the certified. RSD of repeatability and reproducibility value were in the range of 0.43-4.50% and 4.00-8.15% respectively. In §-19
Table 1 The results of PAHs analysis on CRM 1649 (urban dust) PAH Compounds
Average Observed Values
PYR BeP BkF BaP BghiP IP COR FLA
6.3±0.4 2.0±0.1 2.9±0.5 3.9±0.8 3.3±0.5 7.0±0.5
6.9±0.5 4.3±0.3 2.0±0.1 2.5±0.1 3.8±0.2 1.7±0.1 6.8±0.4 6.6±0.3
109 100 86 97 51 94 Mean 90%
order to verify the calibration, a confirmation working standard was run at intervals of 10 samples injection.
3. Results and Discussion The PAHs concentrations in nine classified stages and the total PAH concentration in particulate phase are shown in Figure 1. At urban site, the PAHs concentration in each particle size ranged from 0.33 ng/m3 at the size > 11 µm. to 4.62 ng/m3 at the size < 0.43 µm. with a total PAH concentration of 12.64 ng/m 3. It is found that 83% of the total PAH is distributed in the particle size of 2.1 µm. and 37% is in
the size of less than 0.43 µm. The PAHs in the size of less than 0.43 µm. is the most abundant concentration in the urban sample. At industrial area, the PAHs concentration in each particle size from four sampling sites ranged from 0.01 ng/m3 at the size > 11 µm. to 1.36 ng/m3 at the size < 0.43 µm. with a total PAH concentration of 4.69 ng/m3. The PAHs concentration on size distribution shows the same trend as at urban site, 83% of the total PAH is found in the particle size of 2.1 µm. and 30% is found in the size of less than 0.43 µm. Also the PAHs in the size of less than 0.43 µ m. has the highest concentration in the industrial sample. It is
Figure 1 The PAHs concentration in nine classified stages at urban site, industrial area and rural site
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noticed that the concentration of the PAHs associated with particle size are higher in the smaller size ranking to the lower in the bigger size. This can be explained that since the two main sources of PAHs in urban and industrial area are motor vehicles and industries. Soot from those kind of combustion sources consists primarily of fine particles and has a high PAH content. In addition, a smaller particle has a higher specific surface area and therefore may contain more organic carbon, which allows for more PAH adsorption.6 To compare with the rural site at ERTC as the background area, the PAHs concentration ranged from 0.40 ng/m3 at the size 11-7.0 µm to 2.67 ng/m3. at the size < 0.43 µm. with a total PAH concentration of 9.36 ng/m3. In this area, the largest size of the particulate at > 11 µm. become the second less concentration in the range, also the total PAH in the particle size of 2.1 µm become 72%, it is possible that a part of PAHs in rural area are produced from the biomass burning by the activities of the resident who live around the sampling site such activities often occur in the dry season during December to February of every year. This evidence can cause higher total PAH concentration in the rural area than in the industrial area as shown in this study. However, the PAHs concentration on the particle size distribution ranged from > 11 µm. to < 0.43 µm. from the three studied areas show the same tendency as seen in Figure 2 and the peak of the PAH distributions appear to be exclusively localized at the size less than 0.43 µm. This shows the similar result as the previous study in temperate area.7 PAH concentrations of the particulate and gaseous phases and the ratio of particulate PAH to total PAH are shown in Figure 2. PAHs were classified orderly on the horizontal axis by ring number or, if the ring number were »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡
the same order it was classified by its molecular weight. The data of the three studied area, except for DBacA which shows the abnormal value, show that some PAHs such as PYR, BaA and BeP can be detected regularly in both phases. BkF, BaP, BghiP, DBahA, 3MC, IP and COR are present mostly in particulate phase, while NAP, ANT and FLA are present mostly in gaseous phase. This can be summarized that more than 99% of PAH with 2 to 3 rings exist in the gas phase, and more than 90% of PAH with 5 to 7 rings (high molecular weight) exist in the particulate phase. PAHs with 4 and 5 rings (low molecular weight) exist in both phases. These ratios show the higher value than the PAHs previously measured in the atmosphere of temperate countries.7,8 This evidence may due to the different condition on humidity, ambient temperature and so on. Furthermore, some gaseous PAH levels were more than several orders of magnitude higher than the concentration of particulate PAH. NAP level was the highest of all target PAHs, with the mean concentration in urban and industrial areas of 371 and 407 ng/m3, respectively. However, there are several studies reported that both the gas-particle distribution and particle size distribution are subject to seasonal variations, ambient temperature, vapour pressure of PAH, particulate concentration and the adsorption surface.7 In Figure 2, the concentrations of individual PAH in total particle and gaseous phase at urban site, industrial area and rural site are shown in the same pattern. The total PAH concentration were found highest in urban site and lowest in industrial area with the reason as mentioned above. From this results, the sampling site at ERTC may be not suitable to use as a background area in this study. However, all of PAHs level in the rural site are lower than in the urban site. §-21
In comparing of some PAHs in particulate phase with the previous study of ERTC 3, which have done at the roadside in Bangkok Metropolitan Area, in 1997, the data are shown in Table 2. It is found that
the concentrations of the 5 PAHs, PYR, BkF, BeP, BaP and BghiP, at roadside are about 3-6 and 4-8 times higher than those of urban and rural atmosphere in this study, respectively.
Figure 2 The concentrations of individual PAH in particulate and gaseous phases at urban site (top), industrial area(middle), and rural site (bottom)
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Table 2 Mean concentration of PAHs at the roadside compare with the urban and rural atmosphere Collections Site Previous study ● Pradipat ● Yoawarat ● Pratunam ● Bamsomdet Mean ● ERTC (rural) This study ● OEPP (urban) ● ERTC (rural)
Concentration , ng/m3 BkF BeP BaP
2.61 7.78 26.26 8.69 11.33 3.05
0.83 1.16 2.70 2.40 1.77 0.16
7.40 7.28 21.60 7.57 10.96 1.52
1.83 2.63 4.68 3.14 3.07 0.24
7.55 2.06 24.25 10.90 11.19 1.18
4. Conclusion PAHs in urban, industrial and rural areas were investigated. It was found that in those areas, 70-80% of PAHs target compounds were found in particle size range from 2.1 µm to less than 0.43 µm and most of PAHs which were exist in particle size < 0.43 µm have higher concentration than the other sizes. Moreover, PYR, BaA, BeP and DBacA were distributed between particulate and gaseous phase. NAP, ANT and FLA were found more than 99% in the gaseous phase while BkF, BaP, DBahA, 3MC, IP and COR were found more than 90% in particulate phase. This distribution is comparable for every individual PAH investigated. The comparative studies with other countries such as the urban area of Massachusetts, USA and the outskirts south-east of the town in Southeast Germany using similar sampling techniques are shown in Table 3. 9,10 It was found that the concentration of BaA, BaP, and IP in particulate phase at all sites are within the range as found in Massachusetts, USA. The concentration of BghiP in rural and urban areas are approximately 2 and 3-fold, respectively higher than Southeast Germany and Massachusetts, USA, but the concentration of BghiP at industrial area is within the range as found »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡
in Southeast Germany and Massachusetts, USA. The concentration of COR at all sites are higher than Southeast Germany and Massachusetts, USA of approximately 2-14 folds. Furthermore, the concentration of ANT and FLA, which were under the method of detection limit used in this study, were very much lower when compared with the level found in Germany and U.S.A. From the obtained data, it is expressed that most of PAHs in each area is exist in fine particle size less than 2.1 µm and the concentration of PAHs enriched in fine particles especially in particle size less than 0.43 µm. From this evidence, it is possible that PAHs might be exposed to human health in respiratory system particularly in human lung and surface of the alveoli, and might be contributed to lung cancer due to the mechanism and location of deposition of particulate phase PAHs in the lung are affected by particle size. The large particles (> 11 µm to 3.3 µm) tend to impact on the upper regions of the lung and the small particles (3.3 µm to < 0.43 µm) diffuse to the surface of the alveoli.9 Therefore, it is suggested that PAHs level in ambient air especially in urban area should be further studied in order to estimate the risk assessment and mitigate PAHs exposure to human in this area. §-23
Table 3 Comparative studies on each PAHs concentration in particulate phase with the other countries, ng/m3 PAHs Compounds
PYR BaA BeP DbacA BkF BaP DbahA BghiP 3MC NAP ANT FLA IP COR
3.48 0.45 1.86 0.29 0.63 0.95 0.04 2.35 0.05 nd nd nd 0.83 1.71
2.95 0.26 1.53 0.10 0.47 0.52 0.02 1.42 0.03 nd nd nd 0.62 1.43
1.64 0.16 0.64 0.06 0.19 0.20 0.04 0.77 nd nd nd nd 0.33 0.55
0.68-0.82 0.47-0.62 0.40.0.50 0.60-0.92 0.53-0.84 0.63-1.06 0.57-0.91 -
Massachusetts, MDL USA.10 7.86-8.28 1.58-1.74 1.15-1.19 0.77-0.87 1.20-1.36 0.98-1.08 0.10-0.12
0.04 0.01 0.05 0.01 0.02 0.02 0.02 0.03 0.03 0.08 0.08 0.01 0.02 0.02
Note : nd = Not Detected, MDL : Method Detection Limit of this study
5. Acknowledgment This study was sponsored by the Environmental Agency of Japan. The support of the Environmental Agency of Japan is gratefully acknowledged. We would like to thank the Overseas Environmental Cooperation Center, Japan for project cooperation. We also would like to thank the Maptaput Industrial Estate Office staffs, Thai Olefins CO., Ltd. Staffs, Communication Authority of Thailand staffs in Maptaput Industrial Estate and Wat Sopon for their assistance and allowing us to set up the PAHs sampling sites.
6. References 1. A. Charles, B.B. Menzie, P. Santodonato and J. Santodonato, (1992) Environmental Science Technology, 26, No. 7. 2. C.S. Davis, P. Fellin and R. Otson, (1987), JAPCA, 37, No. 12. 3. International Agency for Research on Cancer, IARC Monographs Volume 32, p. 34. 4. K. Peltonen, and T. Kuljukka, (1995), Journal of Chromatography A, 710, pp. 93-108.
5. R.M. Harrison, D.J.T. Smith and L. Luhana, (1996), Environmental Science Technology, 30, No. 3, pp. 825-832. 6. H.L. Sheu, W.J. Lee, S.J. Lin, G.C. Fang, H.C. Change and W.C. You, (1997), Environmental Pollution, 96, No. 3, pp. 369-382. 7. S.O. Baek, M.E. Goldstone, P.W.W. Kirk, J.N. Lester and R. Perry, (1991), Phase distribution and particle size dependency of polycyclic aromatic hydrocarbons in the urban atmosphere, Chemosphere, 22, pp. 503-520 . 8. Y. Takashi, T. Amagai and H. Matsushita, (1997), Proceedings of a conference held in Kuala Lumpur, Malaysia 4th and 5th September 1997. 9. J.O. Allen, N.M. Dookeran, K.A. Smith, A.F. Sarofim, K. Taghizadeh and A.L. Lafleur, (1996) Environmental Science Technology, 30, pp.1023-1031. 10. J. Schnelle, T. Jansch, K. Wolf, I. Gebefugi, and A. Kettrup, (1995), Chemosphere, 31, No. 4, pp. 3119-3127.
■ ■ ■ ■ ■ ■ ■ §-24
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