- Email: [email protected]
Detection of Pb-LIII edge XANES spectra of urban atmospheric particles combined with simple acid extraction
SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v
Short communication
Detection of Pb-LIII edge XANES spectra of urban atmospheric particles combined with simple acid extraction K. Funasaka a,⁎, T. Tojo a , K. Katahira a , M. Shinya a , T. Miyazaki a , T. Kamiura a , O. Yamamoto a , H. Moriwaki b , H. Tanida c , M. Takaoka d a
Osaka City Institute of Public Health and Environmental Sciences, Tojo-cho 8-34, Tennoji, Osaka 543-0026, Japan Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda, Nagano 386-8567, Japan c Japan Synchrotron Radiation Research Institute, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan d Department of Urban and Environmental Engineering, Kyoto University, Kyoto 606-8501, Japan b
AR TIC LE I N FO
ABS TR ACT
Article history:
Pb-LIII edge XANES spectra of atmospheric particles are directly obtained by fluorescent
Received 4 February 2008
XAFS spectroscopy using a 19-element solid state detector (SSD). Particulate sample was
Received in revised form 15 May 2008
collected on a quartz fiber filter using a high-volume air sampler, and the filter was cut into
Accepted 17 May 2008
small pieces (25 × 25 mm). Then, surface layer of the filter piece was scaled and accumulated
Available online 1 July 2008
in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer enables the measurement of Pb-LIII edge XANES spectra on beamline BL01B1 at SPring-8,
Keywords:
Hyogo, Japan. The shape of the Pb-LIII edge XANES spectra of the particulate sample is
Pb
similar to the shapes of the spectra for PbS, PbCO3, PbSO4 and/or PbCl2. Additionally, the
XAFS
filter sample is also divided into water-soluble, 0.1 M HCl-extractable, and residual fractions
XANES
of Pb compounds by a simple acid extraction procedure. We discuss the possibility of Pb
Atmospheric particles
speciation in the particulate samples with combination of highly sensitive XANES
SPring-8
spectroscopy and simple acid extraction.
Simple acid extraction
© 2008 Elsevier B.V. All rights reserved.
PbS PbCO3
1.
Introduction
Chemical speciation of elements in particulate matter is a more time consuming technique as compared to total mass content analysis such as Neutron Activation Analysis (NAA) and ICP-MS measurement; however, it provides considerable and effective information on the origin, mode of occurrence, biological and physicochemical availability, and fate of metal particles (Smichowski et al., 2005). Pb is universally found in urban atmospheric particles as a contaminant and is commonly associated with neurobehavioral consequences. More-
over, the recent IARC evaluation results in an upgrading of inorganic lead compounds to Group 2A as a probable human carcinogen (Rousseau et al., 2005). It originates from not only anthropogenic exhaust from various industrial processes but also resuspension of road dust and surface soil through natural causes (Shu et al., 2001; Ho et al., 2003; Young et al., 2002; Li et al., 2004). Therefore, the chemical speciation of Pb in environmental particulate samples is important to survey the original source contributions. XAFS and XANES spectroscopy, which can detect metal chemical forms on the basis of electron states around the
⁎ Corresponding author. Tel.: +81 6 6771 3197; fax: +81 6 6772 0676. E-mail address: [email protected] (K. Funasaka). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.05.020
S CIE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
target element, have been performed in order to research the speciation of abundant metals such as Zn in soil (Isaue et al., 2002; Scheinost et al., 2002) and Fe in particulate samples (Qi et al., 2003; Ohta et al., 2006). Further, XAFS spectroscopy pays attention to the chemical speciation of Pb in natural rocks (Takahashi et al., 2002), contaminated soil (Manceau et al., 1996; Morin et al., 1999), and fly ash samples (Takaoka et al., 2005), and it is sometimes applied to bulk samples with a Pb content of less than 1000 ppm. For particulate samples, however, XAFS analysis is more difficult due to a small amount of particle loading on a filter spot that adds to the low Pb content. It is therefore worth considering ways to concentrate particulate mass per filter weight in order to obtain direct Pb-LIII edge XANES spectra in SPring-8, which can produce light that is about one billion times more brilliant than conventional X-ray sources. In addition, the sequential extraction procedure is a widely accepted method that can fractionate sediment samples into different specific phases based on the solubility characteristics of the constituent metallic species (Tessier et al., 1979; Chester et al., 1989; Rauret et al., 1999; Fernandez et al., 2002). Even though some limitations and drawbacks have been pointed out, such as little specificity and the occurrence of re-adsorption, redistribution, and chemical reactions during the operation (Bermond, 2001; Lu et al., 2005; Smichowski et al., 2005) due to chemical interferences, the sequential extraction procedure is still in use for rough speciation of metals in environmental samples (Al-Masri et al., 2006). In this study, more simple acid extraction (Kyotani and Iwatsuki, 2002) was applied in order to supplement direct Pb speciation by XAFS spectroscopy. This paper presents a preliminary study of the combination of XANES spectra and simple acid fractionation for the investigation of trace Pb in the atmospheric samples collected with a high-volume air sampler in urban Osaka, Japan. The main objectives of this study are to (1) obtain direct Pb-LIII edge XANES spectra of urban suspended particles collected on the filter samples using a 19-element SSD, (2) compare the results of XANES spectra with those of the simple acid extraction, and (3) discuss the possibility of chemical speciation of Pb in the particulate samples using the combination of these techniques.
The samplers can collect total suspended particles (TSP) on a filter, and they were operated for 24 h with a suction flow of 1000 L/min simultaneously at both sites. The dates on which the samples analyzed in this study were collected are July 5–6, 2005, November 8–9, 2005, and March 7–8, 2006. Before and after sampling, the filter was weighed in a room at a temperature of 20 °C and a relative humidity of 50%; it was then kept for over 48 h and subsequently stored at −20 °C in a sealed container before use.
2.2.
Materials and methods
2.1.
Samples
Atmospheric particulate samples were collected on a quartz fiber filter (ADVANTEC, QR-100, 203×254 mm) using a high-volume air sampler (SHIBATA, HV-1000) at two monitoring sites in Osaka City. Site I, located in the northwest part of the city (34°42′ N.L. and 135°26′ L.E.), is close to a heavy traffic road of Route 43; out of a total of 56,000 vehicles plying on this road during daytime (for 12 h), 32% are large-sized vehicles. The area around site I also has various small-sized industries such as printing, automobilerelated, and steel companies. Site II is situated in the central area of the city (34°39′ N.L. and 135°31′ L.E.) and is basically located in a residential area. This site is also by the roadside of the Tamatsukurisuji line and has a traffic volume of 19,000 vehicles for 12 h during daytime, with 7.1% of them being large-sized vehicles.
XAFS measurements
The Pb-LIII edge XANES experiments were carried out on Beamline BL01B1 at SPring-8 (Hyogo, Japan), which operates at a ring energy of 8 GeV and with a stored current at 99 mA. The main optics is the standard SPring-8 bending magnet system and the Pb-LIII edge XANES spectra was measured with a Si(111) two-crystal monochromator. In this experimental condition, we can obtain detection limit of Pb as several mg/kg when using a great deal of bulk samples. However, the present filter sample has only a slight amount of particles, therefore, it is necessary to enhance particle loading on the XAFS measuring spot. For this reason, the quartz fiber filter, which collects particulate samples, was cut into small pieces (25 × 25 mm), and then surface layer of the filter piece was scaled and accumulated in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer, which mounts approximately 3 mm of thickness, enables the measurement of Pb-LIII edge XANES spectra based on the bulk information of the particles on beamline BL01B1 at SPring-8, Hyogo, Japan. The XANES spectra of the filter samples were recorded in the fluorescent mode with a 19-element SSD in order to facilitate the high-resolution high-sensitivity measurement of the fluorescence signal of the filter samples. The peak profile of the filter samples was compared with those of reference Pb materials that were recorded in the transmission mode with ionization chambers (Takaoka et al., 2005). The scanning step for the absorbance measurements was 0.3–0.5 eV and the energy was calibrated by setting the pre-edge peak of the Cu foil at 8980.3 eV. All the measurements were carried out at room temperature under ambient air conditions.
2.3.
2.
231
Simple acid extraction
The filter sample was also used for simple acid extraction procedure, which divides particulate samples into watersoluble, 0.1 M HCl-soluble, and residual fractions in accordance with a previous study (Kyotani and Iwatsuki, 2002). In the final step, we used aqua regia (HNO3:HCl = 1:3) decomposition for the residue (Birmili et al., 2006) instead of XRD analysis performed in the original paper. Ten percent of the filter sample was cut and transferred to a glass filter holder already set up a PTFE membrane (ADVANTEC, 47 mmϕ, pore size 0.5 μm), which was sequentially rinsed with 5 mL of ethanol, 5 mL of 70% ethanol, and 20 mL of distilled water in advance. First, 10 mL of distilled water was added to the filter samples and this procedure is repeated four times. The filtrates were gathered as water extraction. Second, 10 mL of 0.1 M HCl is added to the residue and the same procedure is repeated four times. Finally, the entire residue, including the
232
SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
(ET-AAS, Perkin-Elmer, AAnalyst 600) and/or Flame AAS (Shimadzu, AA640-13). Similarly, reference Pb compounds such as PbCl2, PbCO3, PbS, and PbSO4 (all reagent grade) were used for the simple acid extraction in order to compare the acid solubility characteristics between the particulate samples and the reference materials.
Fig. 1 – Examples of Pb-LIII edge XANES spectra of reference materials and atmospheric suspended particles collected with a high-volume air sampler (July 5–6, 2005: sample 1 [roadside] and sample 2 [residential]; November 8–9, 2005: sample 3 [roadside] and sample 4 [residential]; and March 7–8, 2006: sample 5 [roadside] and sample 6 [residential]).
PTFE membrane, is transferred into a glass beaker and decomposed with 20 mL of aqua regia on a hot plate for 1 h. After cooling to room temperature, the residue is filtered (ADVANTEC, No.5C, cellurose), rinsed with water, and the filtrates are reheated almost to dryness and dissolved in 10 mL of 0.2 N nitric acid. Three fractionized solutions were used for the measurement of Pb by Electrothermal Atomic Absorption Spectrometry
3.
Results and discussion
3.1.
XAFS spectroscopy
The Pb-LIII edge XANES spectra of the atmospheric particulate samples are shown in Fig. 1 and they are compared with those of the reference materials. Although the filter samples slightly include Pb in the measuring spot, the use of the highresolution 19-element SSD enables the measurement of PbLIII edge XANES spectra with a single scan. It is suggested that the XANES spectra for site I, corresponding to samples 1, 3, and 5, show relatively smooth peak profiles as compared to those of site II, corresponding to samples 2, 4, and 6. The total suspended particulate concentrations of the samples are as follows: July 5–6, 2005: 51.4 μg/m3 for sample 1 (site I) and 38.0 μg/m3 for sample 2 (site II); November 8–9, 2005: 74.7 μg/m3 for sample 3 (site I) and 50.8 μg/m3 for sample 4 (site II); and March 7–8, 2006: 124 μg/m3 for sample 5 (site I) and 109 μg/m3 for sample 6 (Site II). Therefore, the differences of the particulate concentration, which relate to the environment of the site location, may directly affect the stability of the Pb-LIII XANES spectra. With regard to the Pb-LIII edge XANES spectra, samples 1, 2, 5, and 6 show spectra with similar shapes, with the peak top at 13048 eV. On the other hand, samples 3 and 4, which were collected on November 8–9, 2005, show XANES spectra with a slightly flat shape. Therefore, the difference in the peak shape depends on the sampling days rather than on the difference between the sampling sites. Comparing the Pb-LIII edge XANES spectra of the particulate samples with those of the reference materials, it is suggested that the particles might include chemical forms of PbS, PbCO3 and/or PbSO4. Additionally, the flat peak obtained from samples 3 and 4 indicates the possibility of the existence of PbCl2 in the particulate samples.
Table 1 – Results of simple acid extraction of Pb in the atmospheric particulate samples Water extracted 3
ng-Pb/m
July 5–6, 2005 November 8–9, 2005 March 7–8, 2006
0.1 N-HCl extracted 3
ng-Pb/m
Residue⁎
Total
3
ng-Pb/m3
ng-Pb/m
site I
site II
site I
site II
site I
site II
site I
site II
sample 1 13 (0.10) sample 3 1.7 (0.020) sample 5 10 (0.14)
sample 2 4.2 (0.17) sample 4 1.1 (0.041) sample 6 14 (0.19)
sample 1 53 (0.42) sample 3 34 (0.42) sample 5 26 (0.37)
sample 2 11 (0.43) sample 4 10 (0.40) sample 6 30 (0.41)
sample 1 61 (0.48) sample 3 46 (0.56) sample 5 36 (0.49)
sample 2 10 (0.40) sample 4 14 (0.56) sample 6 29 (0.40)
sample 1 128 (1.0) sample 3 82 (1.0) sample 5 72 (1.0)
sample 2 25 (1.0) sample 4 26 (1.0) sample 6 73 (1.0)
⁎Decomposition by aqua regia.; Detection limit: 0.69 ng-Pb/m3; All data was averaged from duplicate experiment.; The parenthesis shows fraction ratio to total Pb founded.
233
S CIE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
Table 2 – Results of simple acid extraction and normalized leaching ratio of Pb reference materials Initial load mg [as Pb] PbCl2 M.W. 278.1 PbCO3 M.W. 267.2 PbS M.W. 239.3 PbSO4 M.W. 303.3
0.13 0.095 0.089 0.10
Found, mg [as Pb] Water extracted
0.1 M HCl extracted
Residue⁎
Total
0.023 (0.22) 0.097 (0.99) 0.015 (0.22) 0.014 (0.14)
0.0021 (0.021) 0.0012 (0.012) 0.053 (0.78) 0.088 (0.86)
0.104 (1.0) 0.098 (1.0) 0.068 (1.0) 0.102 (1.0)
0.079 (0.76) N.D. (0.00) N.D. (0.00) 0.00024 (0.0023)
Recovery, % 83 103 77 100
⁎Decomposition by aqua regia.; Detection limit: 0.00010 mg as Pb; All data was averaged from duplicate experiment.; Parenthesis shows normalized leaching ratio to total detection.
3.2.
Simple acid extraction
In order to supplement the results from Pb-LIII edge XANES spectra, simple Pb extraction procedure was challenged. Table 1 summarizes the result of the filter sample extraction into water soluble, 0.1 M HCl soluble and residual fraction. The leaching Pb in each fraction was represented as atmospheric concentration, e.g, Pb weight per unit air volume. The number in parentheses represents the ratio of the relative fraction to the total Pb analyzed. Lead in the filter samples is mainly distributed in the 0.1 M HCl-soluble and residual fractions with over 0.8 of fraction ratio in these two fractions. Although the particulate Pb concentration in the samples collected in July and November at site I is higher than that in the samples collected at site II, there seems to be no significant difference between the fraction ratios at the two sites. The sample collected in March, which probably includes yellow sand dust from the Asian continent, shows similar values of the total Pb concentration at both sites. The results of simple acid extraction for PbS, PbSO4, PbCO3 and PbCl2, which are the candidates existing in the particulate sample from XAFS spectroscopy, are also summarized in Table 2. The fractionation behavior varies considerably among the chemical forms of Pb with total recovery of 77–103%. PbCl2 is mainly found in the water-soluble fraction with a fraction ratio of 0.76, and PbCO3 in the 0.1 M HCl-soluble fraction is extracted with a fraction ratio of 0.99. On the contrary, PbS and PbSO4 are mainly recovered from the residual fraction. Comparing the extraction behavior of the filter samples with that of the reference materials, PbCO3, PbS, and PbSO4 appear to be the main components in the particulate samples. Therefore, the chemical forms determined from simple acid extraction are in agreement with those inferred from the XANES peak profile. On the basis of XANES spectroscopy, it is suggested that the fly ash sample collected in the urban incinerator contains mainly PbCl2 and, to a lesser extent, PbS and PbCO3 (Takaoka et al., 2005). However, the small fraction ratio of PbCl2 in the present particulate samples suggests the lesser occurrence of the chloride form in the urban atmosphere. It is also reported that PbSO4 and silica-bound Pb are the dominant forms in the contaminated soil in the vicinity of a battery reclamation area (Manceau et al., 1996), however, there seem no such facilities around the present sampling
sites. Although this study is only limited case, accumulation of the data from various atmospheric particulate samples will be worthwhile in the future in order to estimate original source contribution of the target element through combined analysis with XANES spectroscopy and simple acid extraction.
4.
Conclusion
Direct Pb-LIII edge XANES spectra for urban particulate samples have been obtained by using a 19-element SSD on a beamline BL01B1 at SPring-8. Comparison between the shape of the XANES spectra and additional experiment by simple acid extraction procedure suggests the possibility of particulate Pb existing such as PbS, PbCO3, PbSO4 and/or PbCl2 in the particles. Further studies, e.g., application of XANES spectroscopy and simple acid extraction procedure to various particulate samples, will provide useful information on certain chemical forms of Pb in the urban atmospheric particles.
Acknowledgements This research was conducted as a part of priority research 2007 approved at the Osaka City Institute of Public Health and Environmental Sciences. The content does not necessary reflect the views and policies of the Osaka City local government. We also convey our special thanks to Dr. Kohji Yamamoto for his administrative support.
REFERENCES Al-Masri MS, Al-Kharfan K, Al-Shamali K. Speciation of Pb, Cu and Zn determined by sequential extraction for identification of air pollution sources in Syria. Atmos Environ 2006;40:753–61. Bermond A. Limits of sequential extraction procedures re-examined with emphasis on the role of H+ ion reactivity. Anal Chim Acta 2001;445:79–88. Birmili W, Allen AG, Bary F, Harrison RM. Trace metal concentrations and water solubility in size-fractionated atmospheric particles and influence of road traffic. Environ Sci Technol 2006;40:1144–53. Chester R, Lin FJ, Murphy KJT. A three stage sequential leaching scheme for the characterisation of the sources and environmental
234
SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
mobility of trace metals in the marine aerosol. Environ Technol Lett 1989;10:887–900. Fernandez AJ, Rodriguez MT, Barragan FJ, Jimenez JC. A chemical speciation of trace metals for fine urban particles. Atmos Environ 2002;36:773–80. Ho KF, Lee SC, Chan CK, Yu JC, Chow JC, Yao XH. Characterization of chemical species in PM2.5 and PM10 aerosols in Hong Kong. Atmos Environ 2003;37:31–9. Isaue MP, Laboudigue A, Manceau A, Sarret G, Tiffreau C, Trocellier P, et al. Quantitative Zn speciation in a contaminated dredged sediment by μ-PIXE, μ-SXRF EXAFS spectroscopy and principal component analysis. Geochim Cosmochim Acta 2002;66:1549–67. Kyotani T, Iwatsuki M. Characterization of soluble and insoluble components in PM2.5 and PM10 fractions of airborne particulate matter in Kofu city, Japan. Atmos Environ 2002;36:639–49. Li Z, Hopke PK, Husain L, Qureshi S, Dutkiewicz VA, Schwab JJ, Drewnick F, et al. Source of fine particle composition in New York City. Atmos Environ 2004;38:6521–9. Lu A, Zhang S, Shan X. Time effect on the fractionation of heavy metals in soil. Geoderma 2005;125:225–34. Manceau A, Boisset MC, Sarret G, Hazemann JL, Mench M, Cambier P, et al. Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Sci Technol 1996;30:1540–52. Morin G, Ostergren JD, Juillot F, Ildefonse P, Calas G, Brown Jr GE. XAFS determination of the chemical form of lead in smelter-contaminated soils and mine tailings, Importance of adsorption processes. Am Min 1999;84:420–34. Ohta A, Tsuno H, Kagi H, Kanai Y, Nomura M, Zhang R, et al. Chemical compositions and XANES speciations of Fe, Mn and Zn from aerosols collected in China and Japan during dust events. Geochem J 2006;40:363–76.
Qi J, Zhang M, Feng L, Li X, Xie Z, Sun Z, et al. An EXAFS study on the local structure around iron in atmospheric aerosols collected in the Qingdao area. Molecules 2003;8:31–9. Rauret G, Lopez-Sanchez JF, Sahuquillo A, Rubio R, Davidson C, Ure A, et al. Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials. J Environ Monit 1999;1:57–61. Rousseau MC, Straif K, Siemiatycki J. IARC carcinogen update. Environ Health Perspect 2005;113:A580–1. Scheinost AC, Kretzschmar R, Pfister S, Roberts DR. Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for quantitative zinc speciation in soil. Environ Sci Technol 2002;36:5021–8. Shu J, Dearing JA, Morse AP, Yu L, Yuan N. Determining the sources of atmospheric particles in Shanghai, China, from magnetic and geochemical properties. Atmos Environ 2001;35:2615–25. Smichowski P, Polla G, Gomez D. Metal fractionation of atmospheric aerosols via sequential chemical extraction, a review. Anal Bioanal Chem 2005;381:302–16. Takahashi Y, Usui A, Okumura K, Uruga T, Nomura M, Murakami M, et al. Application of XANES for the determination of oxidation states of Co and Pb in natural ferromanganese nodules. Chem Lett 2002:366–7. Takaoka M, Yamamoto T, Tanaka T, Takeda N, Oshita K, Uruga T. Direct speciation of lead, zinc and antimony in fly ash from waste treatment facilities by XAFS spectroscopy. Phys Scr 2005; T115:943–5. Tessier A, Campbell PGC, Bisson M. Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 1979;51:844–51. Young TM, Heeraman DA, Sirin G, Ashbaugh LL. Resuspension of soil as a source of airborne lead near industrial facilities and highways. Environ Sci Technol 2002;36:2484–90.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v
Short communication
Detection of Pb-LIII edge XANES spectra of urban atmospheric particles combined with simple acid extraction K. Funasaka a,⁎, T. Tojo a , K. Katahira a , M. Shinya a , T. Miyazaki a , T. Kamiura a , O. Yamamoto a , H. Moriwaki b , H. Tanida c , M. Takaoka d a
Osaka City Institute of Public Health and Environmental Sciences, Tojo-cho 8-34, Tennoji, Osaka 543-0026, Japan Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda, Nagano 386-8567, Japan c Japan Synchrotron Radiation Research Institute, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan d Department of Urban and Environmental Engineering, Kyoto University, Kyoto 606-8501, Japan b
AR TIC LE I N FO
ABS TR ACT
Article history:
Pb-LIII edge XANES spectra of atmospheric particles are directly obtained by fluorescent
Received 4 February 2008
XAFS spectroscopy using a 19-element solid state detector (SSD). Particulate sample was
Received in revised form 15 May 2008
collected on a quartz fiber filter using a high-volume air sampler, and the filter was cut into
Accepted 17 May 2008
small pieces (25 × 25 mm). Then, surface layer of the filter piece was scaled and accumulated
Available online 1 July 2008
in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer enables the measurement of Pb-LIII edge XANES spectra on beamline BL01B1 at SPring-8,
Keywords:
Hyogo, Japan. The shape of the Pb-LIII edge XANES spectra of the particulate sample is
Pb
similar to the shapes of the spectra for PbS, PbCO3, PbSO4 and/or PbCl2. Additionally, the
XAFS
filter sample is also divided into water-soluble, 0.1 M HCl-extractable, and residual fractions
XANES
of Pb compounds by a simple acid extraction procedure. We discuss the possibility of Pb
Atmospheric particles
speciation in the particulate samples with combination of highly sensitive XANES
SPring-8
spectroscopy and simple acid extraction.
Simple acid extraction
© 2008 Elsevier B.V. All rights reserved.
PbS PbCO3
1.
Introduction
Chemical speciation of elements in particulate matter is a more time consuming technique as compared to total mass content analysis such as Neutron Activation Analysis (NAA) and ICP-MS measurement; however, it provides considerable and effective information on the origin, mode of occurrence, biological and physicochemical availability, and fate of metal particles (Smichowski et al., 2005). Pb is universally found in urban atmospheric particles as a contaminant and is commonly associated with neurobehavioral consequences. More-
over, the recent IARC evaluation results in an upgrading of inorganic lead compounds to Group 2A as a probable human carcinogen (Rousseau et al., 2005). It originates from not only anthropogenic exhaust from various industrial processes but also resuspension of road dust and surface soil through natural causes (Shu et al., 2001; Ho et al., 2003; Young et al., 2002; Li et al., 2004). Therefore, the chemical speciation of Pb in environmental particulate samples is important to survey the original source contributions. XAFS and XANES spectroscopy, which can detect metal chemical forms on the basis of electron states around the
⁎ Corresponding author. Tel.: +81 6 6771 3197; fax: +81 6 6772 0676. E-mail address: [email protected] (K. Funasaka). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.05.020
S CIE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
target element, have been performed in order to research the speciation of abundant metals such as Zn in soil (Isaue et al., 2002; Scheinost et al., 2002) and Fe in particulate samples (Qi et al., 2003; Ohta et al., 2006). Further, XAFS spectroscopy pays attention to the chemical speciation of Pb in natural rocks (Takahashi et al., 2002), contaminated soil (Manceau et al., 1996; Morin et al., 1999), and fly ash samples (Takaoka et al., 2005), and it is sometimes applied to bulk samples with a Pb content of less than 1000 ppm. For particulate samples, however, XAFS analysis is more difficult due to a small amount of particle loading on a filter spot that adds to the low Pb content. It is therefore worth considering ways to concentrate particulate mass per filter weight in order to obtain direct Pb-LIII edge XANES spectra in SPring-8, which can produce light that is about one billion times more brilliant than conventional X-ray sources. In addition, the sequential extraction procedure is a widely accepted method that can fractionate sediment samples into different specific phases based on the solubility characteristics of the constituent metallic species (Tessier et al., 1979; Chester et al., 1989; Rauret et al., 1999; Fernandez et al., 2002). Even though some limitations and drawbacks have been pointed out, such as little specificity and the occurrence of re-adsorption, redistribution, and chemical reactions during the operation (Bermond, 2001; Lu et al., 2005; Smichowski et al., 2005) due to chemical interferences, the sequential extraction procedure is still in use for rough speciation of metals in environmental samples (Al-Masri et al., 2006). In this study, more simple acid extraction (Kyotani and Iwatsuki, 2002) was applied in order to supplement direct Pb speciation by XAFS spectroscopy. This paper presents a preliminary study of the combination of XANES spectra and simple acid fractionation for the investigation of trace Pb in the atmospheric samples collected with a high-volume air sampler in urban Osaka, Japan. The main objectives of this study are to (1) obtain direct Pb-LIII edge XANES spectra of urban suspended particles collected on the filter samples using a 19-element SSD, (2) compare the results of XANES spectra with those of the simple acid extraction, and (3) discuss the possibility of chemical speciation of Pb in the particulate samples using the combination of these techniques.
The samplers can collect total suspended particles (TSP) on a filter, and they were operated for 24 h with a suction flow of 1000 L/min simultaneously at both sites. The dates on which the samples analyzed in this study were collected are July 5–6, 2005, November 8–9, 2005, and March 7–8, 2006. Before and after sampling, the filter was weighed in a room at a temperature of 20 °C and a relative humidity of 50%; it was then kept for over 48 h and subsequently stored at −20 °C in a sealed container before use.
2.2.
Materials and methods
2.1.
Samples
Atmospheric particulate samples were collected on a quartz fiber filter (ADVANTEC, QR-100, 203×254 mm) using a high-volume air sampler (SHIBATA, HV-1000) at two monitoring sites in Osaka City. Site I, located in the northwest part of the city (34°42′ N.L. and 135°26′ L.E.), is close to a heavy traffic road of Route 43; out of a total of 56,000 vehicles plying on this road during daytime (for 12 h), 32% are large-sized vehicles. The area around site I also has various small-sized industries such as printing, automobilerelated, and steel companies. Site II is situated in the central area of the city (34°39′ N.L. and 135°31′ L.E.) and is basically located in a residential area. This site is also by the roadside of the Tamatsukurisuji line and has a traffic volume of 19,000 vehicles for 12 h during daytime, with 7.1% of them being large-sized vehicles.
XAFS measurements
The Pb-LIII edge XANES experiments were carried out on Beamline BL01B1 at SPring-8 (Hyogo, Japan), which operates at a ring energy of 8 GeV and with a stored current at 99 mA. The main optics is the standard SPring-8 bending magnet system and the Pb-LIII edge XANES spectra was measured with a Si(111) two-crystal monochromator. In this experimental condition, we can obtain detection limit of Pb as several mg/kg when using a great deal of bulk samples. However, the present filter sample has only a slight amount of particles, therefore, it is necessary to enhance particle loading on the XAFS measuring spot. For this reason, the quartz fiber filter, which collects particulate samples, was cut into small pieces (25 × 25 mm), and then surface layer of the filter piece was scaled and accumulated in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer, which mounts approximately 3 mm of thickness, enables the measurement of Pb-LIII edge XANES spectra based on the bulk information of the particles on beamline BL01B1 at SPring-8, Hyogo, Japan. The XANES spectra of the filter samples were recorded in the fluorescent mode with a 19-element SSD in order to facilitate the high-resolution high-sensitivity measurement of the fluorescence signal of the filter samples. The peak profile of the filter samples was compared with those of reference Pb materials that were recorded in the transmission mode with ionization chambers (Takaoka et al., 2005). The scanning step for the absorbance measurements was 0.3–0.5 eV and the energy was calibrated by setting the pre-edge peak of the Cu foil at 8980.3 eV. All the measurements were carried out at room temperature under ambient air conditions.
2.3.
2.
231
Simple acid extraction
The filter sample was also used for simple acid extraction procedure, which divides particulate samples into watersoluble, 0.1 M HCl-soluble, and residual fractions in accordance with a previous study (Kyotani and Iwatsuki, 2002). In the final step, we used aqua regia (HNO3:HCl = 1:3) decomposition for the residue (Birmili et al., 2006) instead of XRD analysis performed in the original paper. Ten percent of the filter sample was cut and transferred to a glass filter holder already set up a PTFE membrane (ADVANTEC, 47 mmϕ, pore size 0.5 μm), which was sequentially rinsed with 5 mL of ethanol, 5 mL of 70% ethanol, and 20 mL of distilled water in advance. First, 10 mL of distilled water was added to the filter samples and this procedure is repeated four times. The filtrates were gathered as water extraction. Second, 10 mL of 0.1 M HCl is added to the residue and the same procedure is repeated four times. Finally, the entire residue, including the
232
SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
(ET-AAS, Perkin-Elmer, AAnalyst 600) and/or Flame AAS (Shimadzu, AA640-13). Similarly, reference Pb compounds such as PbCl2, PbCO3, PbS, and PbSO4 (all reagent grade) were used for the simple acid extraction in order to compare the acid solubility characteristics between the particulate samples and the reference materials.
Fig. 1 – Examples of Pb-LIII edge XANES spectra of reference materials and atmospheric suspended particles collected with a high-volume air sampler (July 5–6, 2005: sample 1 [roadside] and sample 2 [residential]; November 8–9, 2005: sample 3 [roadside] and sample 4 [residential]; and March 7–8, 2006: sample 5 [roadside] and sample 6 [residential]).
PTFE membrane, is transferred into a glass beaker and decomposed with 20 mL of aqua regia on a hot plate for 1 h. After cooling to room temperature, the residue is filtered (ADVANTEC, No.5C, cellurose), rinsed with water, and the filtrates are reheated almost to dryness and dissolved in 10 mL of 0.2 N nitric acid. Three fractionized solutions were used for the measurement of Pb by Electrothermal Atomic Absorption Spectrometry
3.
Results and discussion
3.1.
XAFS spectroscopy
The Pb-LIII edge XANES spectra of the atmospheric particulate samples are shown in Fig. 1 and they are compared with those of the reference materials. Although the filter samples slightly include Pb in the measuring spot, the use of the highresolution 19-element SSD enables the measurement of PbLIII edge XANES spectra with a single scan. It is suggested that the XANES spectra for site I, corresponding to samples 1, 3, and 5, show relatively smooth peak profiles as compared to those of site II, corresponding to samples 2, 4, and 6. The total suspended particulate concentrations of the samples are as follows: July 5–6, 2005: 51.4 μg/m3 for sample 1 (site I) and 38.0 μg/m3 for sample 2 (site II); November 8–9, 2005: 74.7 μg/m3 for sample 3 (site I) and 50.8 μg/m3 for sample 4 (site II); and March 7–8, 2006: 124 μg/m3 for sample 5 (site I) and 109 μg/m3 for sample 6 (Site II). Therefore, the differences of the particulate concentration, which relate to the environment of the site location, may directly affect the stability of the Pb-LIII XANES spectra. With regard to the Pb-LIII edge XANES spectra, samples 1, 2, 5, and 6 show spectra with similar shapes, with the peak top at 13048 eV. On the other hand, samples 3 and 4, which were collected on November 8–9, 2005, show XANES spectra with a slightly flat shape. Therefore, the difference in the peak shape depends on the sampling days rather than on the difference between the sampling sites. Comparing the Pb-LIII edge XANES spectra of the particulate samples with those of the reference materials, it is suggested that the particles might include chemical forms of PbS, PbCO3 and/or PbSO4. Additionally, the flat peak obtained from samples 3 and 4 indicates the possibility of the existence of PbCl2 in the particulate samples.
Table 1 – Results of simple acid extraction of Pb in the atmospheric particulate samples Water extracted 3
ng-Pb/m
July 5–6, 2005 November 8–9, 2005 March 7–8, 2006
0.1 N-HCl extracted 3
ng-Pb/m
Residue⁎
Total
3
ng-Pb/m3
ng-Pb/m
site I
site II
site I
site II
site I
site II
site I
site II
sample 1 13 (0.10) sample 3 1.7 (0.020) sample 5 10 (0.14)
sample 2 4.2 (0.17) sample 4 1.1 (0.041) sample 6 14 (0.19)
sample 1 53 (0.42) sample 3 34 (0.42) sample 5 26 (0.37)
sample 2 11 (0.43) sample 4 10 (0.40) sample 6 30 (0.41)
sample 1 61 (0.48) sample 3 46 (0.56) sample 5 36 (0.49)
sample 2 10 (0.40) sample 4 14 (0.56) sample 6 29 (0.40)
sample 1 128 (1.0) sample 3 82 (1.0) sample 5 72 (1.0)
sample 2 25 (1.0) sample 4 26 (1.0) sample 6 73 (1.0)
⁎Decomposition by aqua regia.; Detection limit: 0.69 ng-Pb/m3; All data was averaged from duplicate experiment.; The parenthesis shows fraction ratio to total Pb founded.
233
S CIE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
Table 2 – Results of simple acid extraction and normalized leaching ratio of Pb reference materials Initial load mg [as Pb] PbCl2 M.W. 278.1 PbCO3 M.W. 267.2 PbS M.W. 239.3 PbSO4 M.W. 303.3
0.13 0.095 0.089 0.10
Found, mg [as Pb] Water extracted
0.1 M HCl extracted
Residue⁎
Total
0.023 (0.22) 0.097 (0.99) 0.015 (0.22) 0.014 (0.14)
0.0021 (0.021) 0.0012 (0.012) 0.053 (0.78) 0.088 (0.86)
0.104 (1.0) 0.098 (1.0) 0.068 (1.0) 0.102 (1.0)
0.079 (0.76) N.D. (0.00) N.D. (0.00) 0.00024 (0.0023)
Recovery, % 83 103 77 100
⁎Decomposition by aqua regia.; Detection limit: 0.00010 mg as Pb; All data was averaged from duplicate experiment.; Parenthesis shows normalized leaching ratio to total detection.
3.2.
Simple acid extraction
In order to supplement the results from Pb-LIII edge XANES spectra, simple Pb extraction procedure was challenged. Table 1 summarizes the result of the filter sample extraction into water soluble, 0.1 M HCl soluble and residual fraction. The leaching Pb in each fraction was represented as atmospheric concentration, e.g, Pb weight per unit air volume. The number in parentheses represents the ratio of the relative fraction to the total Pb analyzed. Lead in the filter samples is mainly distributed in the 0.1 M HCl-soluble and residual fractions with over 0.8 of fraction ratio in these two fractions. Although the particulate Pb concentration in the samples collected in July and November at site I is higher than that in the samples collected at site II, there seems to be no significant difference between the fraction ratios at the two sites. The sample collected in March, which probably includes yellow sand dust from the Asian continent, shows similar values of the total Pb concentration at both sites. The results of simple acid extraction for PbS, PbSO4, PbCO3 and PbCl2, which are the candidates existing in the particulate sample from XAFS spectroscopy, are also summarized in Table 2. The fractionation behavior varies considerably among the chemical forms of Pb with total recovery of 77–103%. PbCl2 is mainly found in the water-soluble fraction with a fraction ratio of 0.76, and PbCO3 in the 0.1 M HCl-soluble fraction is extracted with a fraction ratio of 0.99. On the contrary, PbS and PbSO4 are mainly recovered from the residual fraction. Comparing the extraction behavior of the filter samples with that of the reference materials, PbCO3, PbS, and PbSO4 appear to be the main components in the particulate samples. Therefore, the chemical forms determined from simple acid extraction are in agreement with those inferred from the XANES peak profile. On the basis of XANES spectroscopy, it is suggested that the fly ash sample collected in the urban incinerator contains mainly PbCl2 and, to a lesser extent, PbS and PbCO3 (Takaoka et al., 2005). However, the small fraction ratio of PbCl2 in the present particulate samples suggests the lesser occurrence of the chloride form in the urban atmosphere. It is also reported that PbSO4 and silica-bound Pb are the dominant forms in the contaminated soil in the vicinity of a battery reclamation area (Manceau et al., 1996), however, there seem no such facilities around the present sampling
sites. Although this study is only limited case, accumulation of the data from various atmospheric particulate samples will be worthwhile in the future in order to estimate original source contribution of the target element through combined analysis with XANES spectroscopy and simple acid extraction.
4.
Conclusion
Direct Pb-LIII edge XANES spectra for urban particulate samples have been obtained by using a 19-element SSD on a beamline BL01B1 at SPring-8. Comparison between the shape of the XANES spectra and additional experiment by simple acid extraction procedure suggests the possibility of particulate Pb existing such as PbS, PbCO3, PbSO4 and/or PbCl2 in the particles. Further studies, e.g., application of XANES spectroscopy and simple acid extraction procedure to various particulate samples, will provide useful information on certain chemical forms of Pb in the urban atmospheric particles.
Acknowledgements This research was conducted as a part of priority research 2007 approved at the Osaka City Institute of Public Health and Environmental Sciences. The content does not necessary reflect the views and policies of the Osaka City local government. We also convey our special thanks to Dr. Kohji Yamamoto for his administrative support.
REFERENCES Al-Masri MS, Al-Kharfan K, Al-Shamali K. Speciation of Pb, Cu and Zn determined by sequential extraction for identification of air pollution sources in Syria. Atmos Environ 2006;40:753–61. Bermond A. Limits of sequential extraction procedures re-examined with emphasis on the role of H+ ion reactivity. Anal Chim Acta 2001;445:79–88. Birmili W, Allen AG, Bary F, Harrison RM. Trace metal concentrations and water solubility in size-fractionated atmospheric particles and influence of road traffic. Environ Sci Technol 2006;40:1144–53. Chester R, Lin FJ, Murphy KJT. A three stage sequential leaching scheme for the characterisation of the sources and environmental
234
SC IE N CE OF T H E TOT AL E N V I RO N ME N T 4 0 3 ( 2 00 8 ) 2 3 0–2 34
mobility of trace metals in the marine aerosol. Environ Technol Lett 1989;10:887–900. Fernandez AJ, Rodriguez MT, Barragan FJ, Jimenez JC. A chemical speciation of trace metals for fine urban particles. Atmos Environ 2002;36:773–80. Ho KF, Lee SC, Chan CK, Yu JC, Chow JC, Yao XH. Characterization of chemical species in PM2.5 and PM10 aerosols in Hong Kong. Atmos Environ 2003;37:31–9. Isaue MP, Laboudigue A, Manceau A, Sarret G, Tiffreau C, Trocellier P, et al. Quantitative Zn speciation in a contaminated dredged sediment by μ-PIXE, μ-SXRF EXAFS spectroscopy and principal component analysis. Geochim Cosmochim Acta 2002;66:1549–67. Kyotani T, Iwatsuki M. Characterization of soluble and insoluble components in PM2.5 and PM10 fractions of airborne particulate matter in Kofu city, Japan. Atmos Environ 2002;36:639–49. Li Z, Hopke PK, Husain L, Qureshi S, Dutkiewicz VA, Schwab JJ, Drewnick F, et al. Source of fine particle composition in New York City. Atmos Environ 2004;38:6521–9. Lu A, Zhang S, Shan X. Time effect on the fractionation of heavy metals in soil. Geoderma 2005;125:225–34. Manceau A, Boisset MC, Sarret G, Hazemann JL, Mench M, Cambier P, et al. Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Sci Technol 1996;30:1540–52. Morin G, Ostergren JD, Juillot F, Ildefonse P, Calas G, Brown Jr GE. XAFS determination of the chemical form of lead in smelter-contaminated soils and mine tailings, Importance of adsorption processes. Am Min 1999;84:420–34. Ohta A, Tsuno H, Kagi H, Kanai Y, Nomura M, Zhang R, et al. Chemical compositions and XANES speciations of Fe, Mn and Zn from aerosols collected in China and Japan during dust events. Geochem J 2006;40:363–76.
Qi J, Zhang M, Feng L, Li X, Xie Z, Sun Z, et al. An EXAFS study on the local structure around iron in atmospheric aerosols collected in the Qingdao area. Molecules 2003;8:31–9. Rauret G, Lopez-Sanchez JF, Sahuquillo A, Rubio R, Davidson C, Ure A, et al. Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials. J Environ Monit 1999;1:57–61. Rousseau MC, Straif K, Siemiatycki J. IARC carcinogen update. Environ Health Perspect 2005;113:A580–1. Scheinost AC, Kretzschmar R, Pfister S, Roberts DR. Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for quantitative zinc speciation in soil. Environ Sci Technol 2002;36:5021–8. Shu J, Dearing JA, Morse AP, Yu L, Yuan N. Determining the sources of atmospheric particles in Shanghai, China, from magnetic and geochemical properties. Atmos Environ 2001;35:2615–25. Smichowski P, Polla G, Gomez D. Metal fractionation of atmospheric aerosols via sequential chemical extraction, a review. Anal Bioanal Chem 2005;381:302–16. Takahashi Y, Usui A, Okumura K, Uruga T, Nomura M, Murakami M, et al. Application of XANES for the determination of oxidation states of Co and Pb in natural ferromanganese nodules. Chem Lett 2002:366–7. Takaoka M, Yamamoto T, Tanaka T, Takeda N, Oshita K, Uruga T. Direct speciation of lead, zinc and antimony in fly ash from waste treatment facilities by XAFS spectroscopy. Phys Scr 2005; T115:943–5. Tessier A, Campbell PGC, Bisson M. Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 1979;51:844–51. Young TM, Heeraman DA, Sirin G, Ashbaugh LL. Resuspension of soil as a source of airborne lead near industrial facilities and highways. Environ Sci Technol 2002;36:2484–90.