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EDX for studying the distribution of air pollutants in the surroundings of the emission source
ENVIRONMENTAL
POLLUTION
ELSEVIER
Environmental Pollution 9 (1998) 361-363
The use of SEM/EDX for studying the distribution of air pollutants in the surroundings of the emission source Heikki Haapala Department of Limnology and Environmental Protection, PO Box 27, Viikki A-Building, FIN-O0014 University of Helsinki, Helsinki, Finland Received 7 February 1997; accepted 11 December 1997
Abstract
A new application of SEM/EDX-methods to study the distribution of air pollutants in the surroundings of an emission source is described. An energy dispersive X-ray microanalyzer (EDX) connected to a scanning electron microscope (SEM) was used to measure the amount of several elements on the surface of Scots pine bark. To test this method, bark samples were collected near a limestone quarry and plant. The results indicated that the pollutant gradient in the surroundings of the emission source was clearest, when this new method was used. The coefficientof determination (R2) for calcium on pine bark was as high as 0.99, whereas in the same study line, measurements of total Ca content of pine needles and soil humus yielded R2 values of 0.46 and 0.74, respectively. © 1998 Elsevier Science Ltd. All rights reserved. Keywords: SEM; EDX; Air pollutants; Scots pine; Bark; Calcium
1. Introduction
A scanning electron microscope (SEM) coupled with an energy dispersive X-ray microanalyzer (EDX) has been used for quantitative element analysis in many air pollution studies (e.g. Dzubay et al., 1984; Fiedler et al., 1990; Favali et al., 1991; Lawrey, 1977; Stevens et al., 1993, 1996). Meinander (1994) and Juhanoja and Meinander (1994) used SEM/EDX for studying the elemental composition of airborne particles on the needles of Scots pine. These studies were restricted to particles whose diameter was greater than 2/zm. Similar studies have been performed by Mankovskfi (1994). Garty et al. (1993), Stelzer et al. (1988), Marienfeld and Stelzer (1993) and Marienfeld et al. (1995) have used other SEM/EDX-applications. The aim of this study was to obtain information about the quantities of all impurities, including those which are not visible in the normal SEM range. For this purpose, a new application for the SEM/EDX-methods was developed. In this article the results of a test line are described.
2. Materials and methods
The material for this study was collected in the vicinity of a limestone quarry and plant in Kalkldranta, 026%7491/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PII: S0269-749 ! (98)00025-6
which is situated in the Gulf of Finland, 30 km east of Helsinki. The surroundings of the plant are polluted by the emissions of the plant, mainly calcium, which has an alkalinizing effect on the environment, for instance on soil (Huttunen et al., 1990; Myllyvirta and Henriksson, 1995). The samples of pine bark were collected from six sample plots on 26 March 1996, along a line to the northeast (the main wind direction) at distances of 150, 290, 360, 490, 980 and 1300m from the plant. The samples were taken on the southwestern side of the trunk, i.e. the most susceptible side, at a height of 1.52 m. The sample trees were selected in places where no special protection (e.g. topography, other trees) prevented the free flow of air pollutants from the direction of the emission source. The analyses were performed in the laboratory of the company MIKROFOKUS OY. The samples were airdried in paper bags, then mounted on sample stubs and coated with gold by a JEOL Fine Coat Ion Sputter JFC-1100 coating unit. The preparations were examined w i t h a J E O L J S M 840 scanning electron microscope and a JEOL Semaphore image recording system operating at 15 kV. Analyses were performed directly in the SEM by the PGT Imix EDX microanalyser. The voltage for the energy dispersive analysis was 15 kV, and the time of X-ray collection 60 s.
H. Haapala/EnvironmentalPollution 9 (1998) 361-363
362
For each sample plot 40 points were analyzed on four different bark samples. A 3000-fold magnification was used for X-ray collection, which formed a surface of about 450ttm 2. The difference to other SEM/EDXapplications used earlier was that the total element contents of the whole concerned surface could be measured, including those which were not visible as particles in the normal SEM range. This made it possible to obtain information about the quantities of all impurities. In earlier studies (see Introduction) only the element composition of separate particles has been studied. The measurements of element content for calcium, magnesium, sulfur, silicon, aluminum, potassium and fluorine were made as follows. Calculation of the height of each element peak was made with a scale from 0 to 5 using a separate transparent dial plate. Standard preparations of elements were made for standardization and calibration of the measurements. In the case of calcium, for example, different concentrations of CaC12-solutions were mixed with active carbon, water was evaporated and the C-CaCl2-mixture was spread on a plastic film. These preparations were used for standardization. A standard trendline was computed for the standard measurements (Fig. 1). The equation of this trendline was used to count the element content on the surface of the study material. The preparation of reference materials is t,2
1
0,8
~ 0,6 X
y = 1.8761X + 0,0033
0,4
0,2
0 0,1
0,2
0,3
0,4
0,5
0,7
0,6
mg C a I ram2
Fig. 1. Standard calibration for calcium by SEM/EDX. EDX-units mean the units (scale 0-5) of the transparent dial plate used for the measurement of Ca-peaks (see Materials and methods). 2,5-
2 y = -SE-CGX~ ÷ 1E-O~= - 0,0123~ + 3,7643
¢E 1,5
F ~ 0,5
o
= '
i
i
e
i
i
i 1400
distance ( m )
Fig. 2. Calcium on pine bark surface on the study line.
under further development. Therefore, the results of this study are given only for calcium.
3. Results
Calcium is the main component of the emissions of the limestone quarry and plant. Its accumulation in pine needles and soil has been studied previously (Huttunen et al., 1990; Myllyvirta and Henriksson, 1995). On the surface of the pine bark the Ca-content was very high near the plant, decreasing rapidly with increasing distance (Fig. 2). When the Ca-content as a function of the distance is calculated, the coefficient of determination is very high (R2=0.99), indicating the completely dominant role of the limestone plant in the pine bark surface Ca-content on the study line. On the same study line, total calcium content of pine needles and extractable Ca-content of humus have been analyzed by Myllyvirta and Henriksson (1995). In both cases, Ca-content was very high in the vicinity of the pollution source and decreased with increasing distance. However, the coefficient of determination was much lower than in this study: R 2 = 0.46 in needle analyses and 0.74 in humus analyses. When total biomass of pine needles and soil humus are used, many other factors, in addition to the pollution load, have an effect on the results. Therefore, such studies do not give as exact a picture regarding the effect of air pollution as does the measurement of pollution load on the surface of pine bark. This method has been tested by the author in the surroundings of many other emission sources and it has proved to be useful under different conditions. Good applicability was found under the multi-pollutant load of many large industrial and energy production plants on both sides of the Russian-Estonian boundary as well as in the vicinity of a steel factory and a small wastemetal plant, both on the southern coast of Finland.
4. Conclusions
SEM/EDX has been used for the identification and counting of pollutant particles on the surfaces of biological materials. Using the present application, it is possible to quantitatively measure the total pollutant element content on the surface of biological materials, including impurities that are not visible in the normal SEM range. Compared with other methods used traditionally in pollutant studies, this method gives much more exact results when the distribution of particulate emissions in the surroundings of the pollutant source is studied. The method is also very practical under conditions where many pollutant sources act simultaneously. However, in
H. Haapala/ En vironmental Pollution 9 (1998) 361-363
m a n y cases it s h o u l d be c o m b i n e d w i t h o t h e r m e t h o d s . F o r different p u r p o s e s , m o d i f i c a t i o n s o f this m e t h o d are required.
Acknowledgements I a m very t h a n k f u l t o the p e r s o n n e l o f the l a b o r a t o r y o f the M i k r o f o k u s C o m p a n y , n a m e l y to S i m o L e h t i n e n , M.Sc., a n d to r e s e a r c h scientist S e p p o H o r n i t s k y j , as well as to p r e p a r a t o r M a t t i Viitasaari, U n i v e r s i t y o f Helsinki, for their very v a l u a b l e advice a n d help in the l a b o r a t o r y w o r k . T h a n k s are also d u e to P a a v o T a m m i n e n , M.Sc., for his w o r k to d e v e l o p the reference m a t e r i a l s o f this study. I also t h a n k D r C a r o l N o r r i s for revising the English o f this p a p e r .
References Dzubay, T.G., Stevens, R.K., Balfour, W.D., Williamson, H.J., Cooper, J.A., Core, J.E., De Cesar, R.T., Crutcher, E.R., Dattner, S.L., Davis, B.L., Heisler, S.L., Shah, J.J., Hopke, P.K., Johnson, D.L., 1984. Interlaboratory comparison of receptor model results for Houston aerosol. Atmospheric Environment 18, 1555-1566. Favali, M.A., Corradi, M.G., Fossati, F., 1991. X-ray microanalysis and uitrastructure of lichens from polluted and unpolluted areas. In: Gorsuch, J.W., Lower, W.R., Wang, W., Lewis, M.A. (Eds.). Plants for Toxicity Assessment: Second Volume, ASTM STP 1115. American Society for Testing and Materials, Philadelphia, pp. 276-284. Fiedler, H.J., Baronius, G., Ehrig, F., 1990. Rasterelektronenmikroskopische und chemische Untersuchungen griiner und chlorotischer Nadeln eines immissionsgesch/idigten Kiefern bestandes. Flora 184, 91-101. Garty, J., Karary, Y., Harel, J., 1993. The impact of air pollution on the integrity of cell membranes and chlorophyll in the lichen Ramalina duriaei (De Not.) Bagl. transplanted to industrial sites in
363
Israel. Archives of Environmental Contamination and Toxicology 24, 455-460. Huttunen, S., Manninen, S., MyUyvirta, T., 1990. Raportti Oy Lohja Ab:n Sipoon tehtaan ympiristrvaikutuksista. (A report on the environmental effects of the limestone plant of the company Oy Lohja Ab at Sipoo.) It~i-Uudenmaan ja Porvoonjoen vesienaja ilmansuojelyhdistys r.y., Porvoo. Juhanoja, J., Meinander, O., 1994. SEM/EDS-analysis of anthropogenic particles on needle surfaces. In: Tammi, R., Sorvari, R. (Eds.). Extended Abstracts of the 46th Annual Meeting of the Scandinavian Society for Electron Microscopy, Kuopio, pp. 94-95. Lawrey, J.D., 1977. X-Ray emission microanalysis of Cladonia cristatella from a coal strip-mining area in Ohio. Mycologia 69, 855-860. Mankovskfi, B., 1994. Airborne sulphur and heavy metal pollution in the environment of a thermal power plant. Ecology (Bratislava) 13, 207-217. Marianfeld, S., SteLzer, R., 1993. X-ray microanalyses in Al-treated Avena sativa plants. Journal of Plant Physiology 141,569-573. Marienfeld, S., Lehmann, H., Stelzer, R., 1995. Ultrastructural investigations and EDX-analyses of Al-treated oat (Arena sativa) roots. Plant and Soil 171,167-173. Meinander, O., 1994. Eestin palavan kiven voimalaitosten pii~trist,i" aiheutuvan hiukkaslaskeuman koostumus. (The composition of the particle deposition from the emissions of the oil-shale energy plants in Estonia.) Ilmatieteen laitos, nmanlaatuosasto, Helsinki. Myllyvirta, T., Henriksson, M., 1995. Tutkimus Nordkalk Oy Ab Sipoon kalkkitehtaan ymp~iristfvaikutuksista 1994-1995. (Studies on the environmental effects of the limestone plant of the company Nordkalk Oy Ab at Sipoo.) It~i-Uudenmaan ja Porvoonjoen vesienja ilmansuojeluyhdistys r.y., Porvoo. Stelzer, R., Kuo, J., Koyro, H.-W., 1988. Substitution of Na ÷ by K ÷ in tissues and root vacuoles of barley (Hordeum vulgare L. cv Aramir). Journal of Plant Physiology 132, 671-677. Stevens, R., Pinto, J., Mamane, Y., Ondov, J., Abdulraheem, M., Al-Majed, N., Sadek, M., Cofer, W., EUenson, W., Kellogg, R., 1993. Chemical and physical properties of emissions from Kuwaiti oil fires. Water Science and Technology 27, 223-233. Stevens, R.K., Pinto, J.P., Mamane, Y., Willis, R.D., 1996. Characterization and source apportionment of particulate matter in the Czech republic. Journal of Aerosol Science 27 (Suppl. 1), $685-$686.
POLLUTION
ELSEVIER
Environmental Pollution 9 (1998) 361-363
The use of SEM/EDX for studying the distribution of air pollutants in the surroundings of the emission source Heikki Haapala Department of Limnology and Environmental Protection, PO Box 27, Viikki A-Building, FIN-O0014 University of Helsinki, Helsinki, Finland Received 7 February 1997; accepted 11 December 1997
Abstract
A new application of SEM/EDX-methods to study the distribution of air pollutants in the surroundings of an emission source is described. An energy dispersive X-ray microanalyzer (EDX) connected to a scanning electron microscope (SEM) was used to measure the amount of several elements on the surface of Scots pine bark. To test this method, bark samples were collected near a limestone quarry and plant. The results indicated that the pollutant gradient in the surroundings of the emission source was clearest, when this new method was used. The coefficientof determination (R2) for calcium on pine bark was as high as 0.99, whereas in the same study line, measurements of total Ca content of pine needles and soil humus yielded R2 values of 0.46 and 0.74, respectively. © 1998 Elsevier Science Ltd. All rights reserved. Keywords: SEM; EDX; Air pollutants; Scots pine; Bark; Calcium
1. Introduction
A scanning electron microscope (SEM) coupled with an energy dispersive X-ray microanalyzer (EDX) has been used for quantitative element analysis in many air pollution studies (e.g. Dzubay et al., 1984; Fiedler et al., 1990; Favali et al., 1991; Lawrey, 1977; Stevens et al., 1993, 1996). Meinander (1994) and Juhanoja and Meinander (1994) used SEM/EDX for studying the elemental composition of airborne particles on the needles of Scots pine. These studies were restricted to particles whose diameter was greater than 2/zm. Similar studies have been performed by Mankovskfi (1994). Garty et al. (1993), Stelzer et al. (1988), Marienfeld and Stelzer (1993) and Marienfeld et al. (1995) have used other SEM/EDX-applications. The aim of this study was to obtain information about the quantities of all impurities, including those which are not visible in the normal SEM range. For this purpose, a new application for the SEM/EDX-methods was developed. In this article the results of a test line are described.
2. Materials and methods
The material for this study was collected in the vicinity of a limestone quarry and plant in Kalkldranta, 026%7491/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PII: S0269-749 ! (98)00025-6
which is situated in the Gulf of Finland, 30 km east of Helsinki. The surroundings of the plant are polluted by the emissions of the plant, mainly calcium, which has an alkalinizing effect on the environment, for instance on soil (Huttunen et al., 1990; Myllyvirta and Henriksson, 1995). The samples of pine bark were collected from six sample plots on 26 March 1996, along a line to the northeast (the main wind direction) at distances of 150, 290, 360, 490, 980 and 1300m from the plant. The samples were taken on the southwestern side of the trunk, i.e. the most susceptible side, at a height of 1.52 m. The sample trees were selected in places where no special protection (e.g. topography, other trees) prevented the free flow of air pollutants from the direction of the emission source. The analyses were performed in the laboratory of the company MIKROFOKUS OY. The samples were airdried in paper bags, then mounted on sample stubs and coated with gold by a JEOL Fine Coat Ion Sputter JFC-1100 coating unit. The preparations were examined w i t h a J E O L J S M 840 scanning electron microscope and a JEOL Semaphore image recording system operating at 15 kV. Analyses were performed directly in the SEM by the PGT Imix EDX microanalyser. The voltage for the energy dispersive analysis was 15 kV, and the time of X-ray collection 60 s.
H. Haapala/EnvironmentalPollution 9 (1998) 361-363
362
For each sample plot 40 points were analyzed on four different bark samples. A 3000-fold magnification was used for X-ray collection, which formed a surface of about 450ttm 2. The difference to other SEM/EDXapplications used earlier was that the total element contents of the whole concerned surface could be measured, including those which were not visible as particles in the normal SEM range. This made it possible to obtain information about the quantities of all impurities. In earlier studies (see Introduction) only the element composition of separate particles has been studied. The measurements of element content for calcium, magnesium, sulfur, silicon, aluminum, potassium and fluorine were made as follows. Calculation of the height of each element peak was made with a scale from 0 to 5 using a separate transparent dial plate. Standard preparations of elements were made for standardization and calibration of the measurements. In the case of calcium, for example, different concentrations of CaC12-solutions were mixed with active carbon, water was evaporated and the C-CaCl2-mixture was spread on a plastic film. These preparations were used for standardization. A standard trendline was computed for the standard measurements (Fig. 1). The equation of this trendline was used to count the element content on the surface of the study material. The preparation of reference materials is t,2
1
0,8
~ 0,6 X
y = 1.8761X + 0,0033
0,4
0,2
0 0,1
0,2
0,3
0,4
0,5
0,7
0,6
mg C a I ram2
Fig. 1. Standard calibration for calcium by SEM/EDX. EDX-units mean the units (scale 0-5) of the transparent dial plate used for the measurement of Ca-peaks (see Materials and methods). 2,5-
2 y = -SE-CGX~ ÷ 1E-O~= - 0,0123~ + 3,7643
¢E 1,5
F ~ 0,5
o
= '
i
i
e
i
i
i 1400
distance ( m )
Fig. 2. Calcium on pine bark surface on the study line.
under further development. Therefore, the results of this study are given only for calcium.
3. Results
Calcium is the main component of the emissions of the limestone quarry and plant. Its accumulation in pine needles and soil has been studied previously (Huttunen et al., 1990; Myllyvirta and Henriksson, 1995). On the surface of the pine bark the Ca-content was very high near the plant, decreasing rapidly with increasing distance (Fig. 2). When the Ca-content as a function of the distance is calculated, the coefficient of determination is very high (R2=0.99), indicating the completely dominant role of the limestone plant in the pine bark surface Ca-content on the study line. On the same study line, total calcium content of pine needles and extractable Ca-content of humus have been analyzed by Myllyvirta and Henriksson (1995). In both cases, Ca-content was very high in the vicinity of the pollution source and decreased with increasing distance. However, the coefficient of determination was much lower than in this study: R 2 = 0.46 in needle analyses and 0.74 in humus analyses. When total biomass of pine needles and soil humus are used, many other factors, in addition to the pollution load, have an effect on the results. Therefore, such studies do not give as exact a picture regarding the effect of air pollution as does the measurement of pollution load on the surface of pine bark. This method has been tested by the author in the surroundings of many other emission sources and it has proved to be useful under different conditions. Good applicability was found under the multi-pollutant load of many large industrial and energy production plants on both sides of the Russian-Estonian boundary as well as in the vicinity of a steel factory and a small wastemetal plant, both on the southern coast of Finland.
4. Conclusions
SEM/EDX has been used for the identification and counting of pollutant particles on the surfaces of biological materials. Using the present application, it is possible to quantitatively measure the total pollutant element content on the surface of biological materials, including impurities that are not visible in the normal SEM range. Compared with other methods used traditionally in pollutant studies, this method gives much more exact results when the distribution of particulate emissions in the surroundings of the pollutant source is studied. The method is also very practical under conditions where many pollutant sources act simultaneously. However, in
H. Haapala/ En vironmental Pollution 9 (1998) 361-363
m a n y cases it s h o u l d be c o m b i n e d w i t h o t h e r m e t h o d s . F o r different p u r p o s e s , m o d i f i c a t i o n s o f this m e t h o d are required.
Acknowledgements I a m very t h a n k f u l t o the p e r s o n n e l o f the l a b o r a t o r y o f the M i k r o f o k u s C o m p a n y , n a m e l y to S i m o L e h t i n e n , M.Sc., a n d to r e s e a r c h scientist S e p p o H o r n i t s k y j , as well as to p r e p a r a t o r M a t t i Viitasaari, U n i v e r s i t y o f Helsinki, for their very v a l u a b l e advice a n d help in the l a b o r a t o r y w o r k . T h a n k s are also d u e to P a a v o T a m m i n e n , M.Sc., for his w o r k to d e v e l o p the reference m a t e r i a l s o f this study. I also t h a n k D r C a r o l N o r r i s for revising the English o f this p a p e r .
References Dzubay, T.G., Stevens, R.K., Balfour, W.D., Williamson, H.J., Cooper, J.A., Core, J.E., De Cesar, R.T., Crutcher, E.R., Dattner, S.L., Davis, B.L., Heisler, S.L., Shah, J.J., Hopke, P.K., Johnson, D.L., 1984. Interlaboratory comparison of receptor model results for Houston aerosol. Atmospheric Environment 18, 1555-1566. Favali, M.A., Corradi, M.G., Fossati, F., 1991. X-ray microanalysis and uitrastructure of lichens from polluted and unpolluted areas. In: Gorsuch, J.W., Lower, W.R., Wang, W., Lewis, M.A. (Eds.). Plants for Toxicity Assessment: Second Volume, ASTM STP 1115. American Society for Testing and Materials, Philadelphia, pp. 276-284. Fiedler, H.J., Baronius, G., Ehrig, F., 1990. Rasterelektronenmikroskopische und chemische Untersuchungen griiner und chlorotischer Nadeln eines immissionsgesch/idigten Kiefern bestandes. Flora 184, 91-101. Garty, J., Karary, Y., Harel, J., 1993. The impact of air pollution on the integrity of cell membranes and chlorophyll in the lichen Ramalina duriaei (De Not.) Bagl. transplanted to industrial sites in
363
Israel. Archives of Environmental Contamination and Toxicology 24, 455-460. Huttunen, S., Manninen, S., MyUyvirta, T., 1990. Raportti Oy Lohja Ab:n Sipoon tehtaan ympiristrvaikutuksista. (A report on the environmental effects of the limestone plant of the company Oy Lohja Ab at Sipoo.) It~i-Uudenmaan ja Porvoonjoen vesienaja ilmansuojelyhdistys r.y., Porvoo. Juhanoja, J., Meinander, O., 1994. SEM/EDS-analysis of anthropogenic particles on needle surfaces. In: Tammi, R., Sorvari, R. (Eds.). Extended Abstracts of the 46th Annual Meeting of the Scandinavian Society for Electron Microscopy, Kuopio, pp. 94-95. Lawrey, J.D., 1977. X-Ray emission microanalysis of Cladonia cristatella from a coal strip-mining area in Ohio. Mycologia 69, 855-860. Mankovskfi, B., 1994. Airborne sulphur and heavy metal pollution in the environment of a thermal power plant. Ecology (Bratislava) 13, 207-217. Marianfeld, S., SteLzer, R., 1993. X-ray microanalyses in Al-treated Avena sativa plants. Journal of Plant Physiology 141,569-573. Marienfeld, S., Lehmann, H., Stelzer, R., 1995. Ultrastructural investigations and EDX-analyses of Al-treated oat (Arena sativa) roots. Plant and Soil 171,167-173. Meinander, O., 1994. Eestin palavan kiven voimalaitosten pii~trist,i" aiheutuvan hiukkaslaskeuman koostumus. (The composition of the particle deposition from the emissions of the oil-shale energy plants in Estonia.) Ilmatieteen laitos, nmanlaatuosasto, Helsinki. Myllyvirta, T., Henriksson, M., 1995. Tutkimus Nordkalk Oy Ab Sipoon kalkkitehtaan ymp~iristfvaikutuksista 1994-1995. (Studies on the environmental effects of the limestone plant of the company Nordkalk Oy Ab at Sipoo.) It~i-Uudenmaan ja Porvoonjoen vesienja ilmansuojeluyhdistys r.y., Porvoo. Stelzer, R., Kuo, J., Koyro, H.-W., 1988. Substitution of Na ÷ by K ÷ in tissues and root vacuoles of barley (Hordeum vulgare L. cv Aramir). Journal of Plant Physiology 132, 671-677. Stevens, R., Pinto, J., Mamane, Y., Ondov, J., Abdulraheem, M., Al-Majed, N., Sadek, M., Cofer, W., EUenson, W., Kellogg, R., 1993. Chemical and physical properties of emissions from Kuwaiti oil fires. Water Science and Technology 27, 223-233. Stevens, R.K., Pinto, J.P., Mamane, Y., Willis, R.D., 1996. Characterization and source apportionment of particulate matter in the Czech republic. Journal of Aerosol Science 27 (Suppl. 1), $685-$686.