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Elemental composition and source investigation of particulates suspended in the air of an iron foundry
The Science of the Total Environment, 41 (1985) 13--28 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
13
ELEMENTAL COMPOSITION AND SOURCE INVESTIGATION OF PARTICULATES SUSPENDED IN THE AIR OF AN IRON FOUNDRY
JIQIANG ZHANG, JEANNINE BILLIET and RICHARD DAMS
Institute for Nuclear Sciences, Rijksuniversiteit Gent, Proeftuinstraat 86, B-9000 Gent (Belgium) (Received April 10th, 1984 ; accepted June 9th, 1984) ABSTRACT
In the workshop of an iron foundry suspended particulate matter was daily collected with stationary filtration systems, Andersen cascade impactors and personal samplers. During a two-week period, with a network of sixteen stationary samplers and personal samplers carried by three workers active in the different departments of the workshop, a survey was made of the levels. Some samples were also taken of the major emission sources in the foundry. All samples were analysed by instrumental neutron activation analysis. Data were obtained for 21 elements in all samples, while 15 additional elements could only be detected in the large majority of the samples. F o r visualisation and interpretation of the data computer programs for contour plotting, classification and clustering of the elements and the samples were applied. The size distribution, the air concentration profile delineation and the element clusters indicated the presence of three main groups of elements. The La-group, consisting of lithophilic elements such as Na, K, Mg, Ca, Sc, La, Ce and Eu and associated with large particles, is primarily generated by the pouring, shake-out and moulding process. The Fe-group, with elements such as V, Cr, Mn, Fe, Co, Zn, As, Sb and Ba, originates primarily during fettling and shake-out. A few of these, Mn, Zn, As and Sb, are largely associated with fine particles. The elements Br and C1, which are produced from burning pitch, are nearly evenly distributed throughout the room. The results allow estimates of the impact of the major emission sources on the entire workroom, and of some localized sources in their immediate vicinity. Suggestions for representative sampling locations and indicator elements are obtained from the results.
INTRODUCTION A w o r k s h o p o f a n i r o n f o u n d r y is a m u l t i - s o u r c e a r e a o f p a r t i c u l a t e c o n t a m i n a n t s . O w i n g t o t h e v a r i e t y o f s o u r c e s in s u c h a n a r e a t h e n a t u r e o f p a r t i c u l a t e s s u s p e n d e d in t h e a i r v a r i e s c o n s i d e r a b l y . N o v a l i d a s s e s s m e n t o f the impact of the particulate contaminants on human health can be made without at least some knowledge of the chemical composition and the a e r o d y n a m i c p a r t i c l e size o f t h e c o n t a m i n a n t s . I n a p r e v i o u s p a p e r ( Z h a n g e t al., 1 9 8 1 ) t h e s a m p l i n g t e c h n i q u e s t o b e u s e d f o r t h e m e a s u r e m e n t o f t h e total and respirable suspended particulate matter were discussed. It was shown that after sample collection on Millipore membrane filters, or with 0048-9697/85/$03.30
© 1985 Elsevier Science Publishers B.V.
14 Andersen cascade impactors, instrumental neutron activation analysis allows the quantitative determination of approximately 30 elements in the particulate matter. A second paper (Zhang et al., 1983) described the levels of total and respirable particulate matter encountered in this workshop and the comparison of stationary and personal monitoring in three of the source areas. A number of interesting conclusions could be drawn from this study, based on the results of a sampling network consisting of 16 stationary sampling stations set up in the f o u n d r y and a few personal samplers carried by workers active in different areas of the shop. For respirable particles one to two well-situated stationary size-selective samplers can provide a good estimate of the personal exposure as measured with a personal respirable monitor. In the immediate vicinity of intense point sources of coarse particles, however, stationary sampling cannot be used to estimate the personal exposure to total suspended particulates. The survey of the particulate levels obtained by the network showed large variations in concentration gradients as a function of time. The aim of the present study is to identify the major particulate emission sources in the workshop and to evaluate their impact on the air quality of the entire room by chemical analysis and by measurement of the aerodynamic particle size of the dust collected at the different sampling sites. The distribution patterns of the different elements over the workshop can be visualised with a computer program for contour plotting; classification methods can also be used to group the elements according to their distributions. The composition of the dust collected at the different sampling sites can also provide some information on the impact of different emission sources on the overall levels of contaminants in the shop. Therefore a comparison must be made with the composition of the emission samples collected at the sources.
EXPERIMENTAL
Sampling site and equipment The sampling site, measuring 100 × 50 m was fully described in a previous paper (Zhang et al., 1983); only a scheme of the workshop and the position of the different sampling stations are given here, as illustrated in Fig. 1. Air from fourteen locations in the room, and one outdoor site {16), was sampled with 47 mm diameter membrane filters, pore size 3.0 pm, a t a flowrate of 0.8 m 3 h -1 . The filterholders are fixed at a height of 1.6 m and are oriented downwards. In addition, at three sites (namely 1, 5-1 and 14) the particles are classified according to their aerodynamic particle size with a nine-stage Andersen cascade impacter (ACI) operating at a flowrate of 1.7 m 3 h -1 . Personal total particulate samplers were carried during part of the two-weeklong sampling period by three workers active in the metal pouring- (PT 1), the core-making- (PT 2) and the shake-out departments (PT 3), respectively. In the metal melting and pouring department (A and B in Fig. 1) the molten
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Stationary sampling sites Sampling site for comparison of stationary samplers Personal sampling (station PTI, PR1)
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Fig. 1. Scheme of the workshop and sampling sites. (A) Melting and metal treatment department; (B) pouring lines; (C) moulding machines; (D) shaking-out grid; (E) shotblasting; (F) fettling shop; (G) sand preparation; (H) sand preparation and return sand; (I) core-shop and (J) drying oven.
metal is treated and transferred into the moulds positioned along the pouring lines. The core-making department (I in Fig. 1) is situated in a relatively quiet area of the workshop. Cores, specially formed parts of a mould used to form internal holes in a casting, are made by hand and sprayed or swabbed with "core wash" and baked. Afterwards they are cleaned with pressurised air. In the shake-out department the castings are shaken out of the moulds after they have solidified. This operation is performed by placing the flask containing the mould and casting on a vibrating grid called a "shake-out machine" (D in Fig. 1). The personal samplers consisted of a 37 mm lapel-type filterholder containing a membrane filter. The flowrate was constant at approximately 1.851 min -1 .
Chemical analysis After weighing at constant temperature and humidity (50% RH) the filters and the impaction sheets were pressed into pellets for instrumental neutron activation as described before (Dams et al., 1970). For some 20 elements the reproducibility of the analysis is generally better than 10%. When at least 5 mg dust is collected an additional 10--15 elements can mainly be detected with larger uncertainties. It was found (Zhang et al., 1981) that for a number of easily detected elements the overall reproducibility of the procedure is 7%, of which 5% can be attributed to the sampling.
Sampling period The study lasted 2 weeks (10 working days). To conform with the
16 TABLE 1 MEAN, MAXIMUM AND MINIMUM CONCENTRATIONS OF ELEMENTS (inpgm -3 ) MEASURED AT STATIONARY INDOOR AND OUTDOOR STATIONS Element
Na Mg A1 C1 K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
Geom. mean
41.2 81.5 260 7.6 43.2 88.9 0.040 0.43 0.96 15.0 590 0.13 4.5 0.52 0.12 0.15 0.016 8.40 0.15 0.30 0.0042
Concentration (pg m -3 ) Max. (station)
Min. (station)
107 (14) 184 (14) 1650 (13) 14 (13) 101 (14) 334 (13) 0.153 (13) 6.8 (13) 14.7 (13) 416 (13) 13600 (13) 2.5 (13) 44 (13) 9.6 (13) 0.21 (13) 1.6 (13) 0.038 (14) 171 (13) 0.51 (13) 2,2 (13) 0.0096 (14)
10.7 (3) 19.6 (3) 50 (3) 2.7 (14) 8.5 (3) 28.2 (3) 0.0094 (3) 0.088 (3) 0.20 (3) 6.1 (5-1) 120 (3) 0.029 (3) 2.0 (3) 0.17 (3) 0.09 (14) 0.07 (3) 0.005 (3) 2.3 (5-1) 0.044 (5-2) 0.076 (3) 0.0015 (3)
Outdoor (stat. 16) 0.59 0.23 0.48 0.57 0.38 0.62 0.0001 0.017 0.005 0.049 0.90 0.00077 0.13 0.0085 0.026 0.0077 0.00019 < 0.073 0.00046 0.00075 <:0.00013
w o r k i n g h o u r s a sampling time o f 8 h was c h o s e n and the filters were c h a n g e d daily. O w i n g t o s o m e incidents a few samples are missing so t h a t the n u m b e r o f sampling days varies b e t w e e n 6 and 9. Also the special studies p e r f o r m e d with t h e cascade i m p a c t o r s and the personal samplers lasted o n l y for 2--5 days. T h e d a y - b y - d a y variations o f the c o n c e n t r a t i o n s in t h e air were t y p i c a l l y a f a c t o r o f 2.5, b u t will n o t be discussed in the present paper. Instead a time-averaged m e a n c o n c e n t r a t i o n was calculated f o r all stations. The m e a n values o b t a i n e d for t o t a l s u s p e n d e d particulates varied f r o m a low o f 1 . 3 6 m g m -3 at station 3 t o a high o f 5 1 . 9 m g m -3 at s t a t i o n 13, while t h e m e a n value at the o u t d o o r s t a t i o n 16 was o n l y 0 . 0 3 3 mg m -3 .
RESULTS AND DISCUSSION
Distribution patterns of the elements In Table 1 t h e g e o m e t r i c m e a n values o f the time-averaged c o n c e n t r a t i o n s for 21 elements in t h e air at all sixteen i n d o o r s t a t i o n a r y stations are given. F r o m the c o m p a r i s o n with the c o n c e n t r a t i o n s at t h e o u t d o o r station 16 it is
17 TABLE 2 M A X I M U M A N D MINIMUM C O N C E N T R A T I O N S (in p g m -3) M E A S U R E D A T S T A T I O N A R Y I N D O O R A N D O U T D O O R S T A T I O N S F O R E L E M E N T S WHICH A R E NOT D E T E C T E D IN E V E R Y SAMPLE (--: below limit of detection) Element
Ti Ni Cu Ga Se
Concentration (pg m -3 ) Max. (station)
Min. (station)
O u t d o o r s (stat. 16)
36 (12) 18 (13) 42 (13) 3.8 (12) 0.054(13)
1.6 0.32 0.51 0.025 0.008
0.032 -0.019 0.002
(7) (6) (5-1) (9) (7)
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0.63
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0.006
(6)
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0.031 0.79 0.013 0.18 0.11 0.022 0.37 0.003 0.41
(4) (13) (12) (2) (12) (13) (13) (13) (13)
0.008 0.014 0.0008 0.010 0.003 0.0009 0.010 0.0001 0.016
(5-2) (1) (4) (5-1) (6) (4) (6) (9) (5-1)
--
-0.004 0.00005 0.004 ------
clear that intense emission sources exist for all these elements. To give an idea of the variations the maximum and minimum time-averaged concentrations are given in Table 1. At station 13, at the fettling shop, almost all elements have their peak concentration. In this shop the final refinement of the castings called "finishing" or "fettling" is carried out. The workers remove gates, risers and surface imperfections of the castings by sledge° hammers, friction saws and grinding wheels. Grinding produces rather large fragments of metal and blows a lot of dust into the surrounding air; therefore the fettling shop is the most dusty area of the workroom. The lowest concentrations are found at station 3, which is strongly influenced by the natural convection from a door, and at stations 5-1 and 5-2 in the relatively calm area of the core-making department. Fifteen other elements were detected in a number of samples, but their concentrations often approached the limit of detection of the method. In Table 2 the maximum and minimum values measured are summarised, together with the concentrations measured at o u t d o o r station 16. It is clear that these elements have sources in the workroom; a discussion of these 15 elements will n o t be considered further. Although it is clear from Tables 1 and 2 that the values for all elements largely exceed the o u t d o o r values, they do not approach the Threshold Limit Values (TLV) as established today, with the exception of Fe (Dreisbach, 1974). In the fettling shop the TLV of 1 mg m -3 for Fe is
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C C Fig. 2. Contour plots of the elements in the workshop. La (ngm -3):(A) 0.735;(I) 31.5;(J) 50.4;(K) 80.5;(L) 129;(M) 206; (N) 330. Fe (/~gm-3):(A) 1.45; (J) 61.9;(K) 159;(L) 254;(M) 415;(N) 649;(O) 1040: (P) 1160; (Q) 2660 ;3(R) 4250; (S) 6790; (T) 10900. Br ( n g m - ) : (A) 41.6; (B) 66.5; (C) 106;(D) 209.
19 largely exceeded which is not without hazard as while siderosis is a known effect on the lungs following high exposure to Fe, there is also an increased risk of lung cancer as reported by Friberg et al. {1979). Based on the time-averaged concentrations in the air at all sixteen stations, intermediate concentrations are calculated with a computer program called Contor-Tridim (Op de Beeck, 1978). To visualise the distribution pattern for all 21 elements isoconcentration lines are drawn in a contour diagram. These plots enable us to evaluate the size of different source-areas, and to divide the elements into groups with similar distributions. Three groups could be identified, and for each a representative plot is shown in Fig. 2. The distribution of La is characteristic for a large group of elements, namely Na, K, Cs, Mg, Ca, A1, Sc, La, Ce and Eu. These elements have a major concentration peak in the fettling shop, and a minor one in the pouring department. The distribution of Fe is indicative for a group with V, Cr, Mn, Fe, Co, Zn, Ba, As and Sb with a very sharp peak in the fettling shop. The group of volatile elements consists only of Br and C1 and concentration variations for these elements are very smooth. Element distribution as a function o f particle size An Anderson Cascade Impactor was used to classify the particles as a function of their "aerodynamic diameter" in the pouring, core-making and shake-out departments. The impactor collects the particles in nine different fractions on eight different stages and a back-up filter. Owing to the mechanical construction of the multistage impactor, fifty percent of the mass of the particles collected on stage 0 has an aerodynamic diameter of > 11 pm; fifty percent of the masses of the particles collected on stages 1--7 have aerodynamic diameters of 7.8, 4.7, 3.3, 2.1, 1.1, 0.65 and 0.43, respectively, while particles with smaller aerodynamic diameters are collected by the back-up filter. This allows the construction of size distribution curves as illustrated in Fig. 3, for all elements chemically determined in the collected particles, and also provides an indication of the association of the elements with different particle sizes. At all three locations of the experiment, the elements Na, Mg, A1, K, Ca, Sc, Cr, Fe, Co, Cs, Ba, La, Ce and Eu are shown to be associated exclusively with the "coarser" particles, as illustrated by the size--weight curves of Fe in Fig. 3. Very similar curves were also found for the total of all particles suspended in the foundry (Zhang et al., 1983). Elements such as V, Zn, As and Sb show some association with "coarser" particles, but also with "smaller" particles, indicating that these elements are emitted, at least in part, as volatile compounds. As an illustration, the size--weight curves of the element As is given in Fig. 3. Volatile elements such as C1 and Br are found to be primarily associated with "small" particles in the pouring- and core-making department, but also show to some extent an association with "coarser" particles in the shake-out department (see Fig. 3). The same applies for the element V (not illustrated). An explanation may be that during the shake-out process particles are
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released that are the result of solid--gaseous reactions. That part of the Mn emission in the foundry may take the form of volatile compounds is illustrated in Fig. 3, showing an association of Mn with small particles in the pouring- and core-making department. Morphological studies using a scanning electron microscope (Zhang, 1983) showed that Mn in fact relates with both coarse and fine particles. A similar distribution for Mn was also found in another foundry {Dams et al., 1972).
Composition of foundry dust With the total weight of each sample known, the results can also be expressed in terms of the concentration of the elements in the particulate
21 TABLE 3 MEAN CONCENTRATIONS (in ppm) OF SAMPLES COLLECTED WITH INDOOR STATIONARY AND PERSONAL SAMPLERS AND OF FALLOUT DUST
Element
Stationary stations Geom. mean
Na Mg A1 CI K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
7700 16900 48100 1600 8400 18500 7.2 74 170 2990 108000 24 830 95 23 26 3.0 1520 27 54 0.72
Personal samplers
Max. (station) 10300 23200 66700 5900 11300 27500 9.3 163 297 8880 263000 49 1520 172 79 48 4.35 3320 51 93 1.2
(i) (1) (I) (3) (5-2) (1) (1) (13) (5-1) (13) (13) (3) (13) (3) (3) (1) (13) (1) (1) (1)
Min. (station) PT 1
PT 2
3960 ( 1 3 ) 9000 (13) 31900(13) 268 ( 1 3 ) 1850 (13) 6400 (13) 2.9 (13) 54 (2) 95 (1) 1720 (1) 37800 (1) 13 (1) 570 (14) 42 (1) 4.1 (13) 17 (15) 0.45 (13) 930 (2) 9.8 (13) 29 (12) 0.53 (5-1)
4 5 0 0 10200 59000 19000 30000 66000 2800 760 -1120 15000 23000 6.0 9.8 50 57 585 126 2100 1000 77000 70000 36 16 820 370 120 36 23 36 23 8 2.0 3.7 1.1 0.97 21 38 44 80 0.48 0.95
9700 22000 61000 3600 1160 26000 8.3 62 194 3300 66000 19 1100 70 39 28 4.0 1.1 98 150 1.3
SF
PT 3 10700 17000 44000 1140 12100 12000 9.6 35 82 580 46200 10.6 190 9.6 8.0 25 3.6 510 34 71 0.97
matter. Since in the different areas of the workshop the same activities are repeated all year round, it may be assumed that each stationary sampler collects dust with a typical composition which is largely determined by the neighbouring emission sources. Of all the samples taken at the different sites of the workshop, but excluding those taken by personal samplers, the mean composition was calculated based on daily samples. From these mean compositions a general geometric mean composition for the whole workshop is given in Table 3, together with the m a x i m u m and the minimum values. In order to provide a mathematical basis for the grouping of the elements an element clustering program was applied to the (16 x 21) data set. The classification is carried out with the aid of a computer program, named HADCLU, developed by Op de Beeck {1977, 1980). For an explanation of the clustering strategy and the algorithms and formulae used, the reader is referred to the original publications. The program allows a graphical representation of the clustered data in the form of a dendrogram as illustrated by Fig. 4. All elements are placed equidistant (by choice) on the top. Vertical distances indicate "dissimilarities" between elements as calculated by the computer program. They have no absolute
22 No Sc AI Cs Eu K Ca La Ce V Co Ba Fe Mn As Sb Zn M
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sample from the fettling shop. meaning and should only be compared within a single classification. Groups of elements, called clusters, can be identified as showing "large" dissimilatities as compared to the "small" dissimilarities between the elements of a single group. For the element classification of the foundry dust, the calculation was carried out using the mean composition of all samples taken at the different stations in the foundry except the samples from station 13. The fettling procedure carried out at this station must be considered as a source of only local importance in view of the very large size of the emitted particles, The composition of the fallout dust collected on t o p of protecting casework of some machinery in the vicinity of the largest shake-out machine of the workshop as given in Table 3 (SF), and the composition of the personal samples in Table 3 (PT1, PT2, PT3 ) are also included in the data; the resulting dendrogram is given in Fig. 4. Examination of the dendrogram at a dissimilarity level of 0.045, shows that four groups of elements can be distinguished corresponding to the earlier defined La, Fe and Br groups, except for the somewhat surprising group of the elements Mg and Cr. Analyses of the different sources in the room (see section source identification and Table 4) later showed that the core-wash used in the core-making shop also contains large amounts of Cr and Mg. This core-wash is spread onto the cores and then removed after hardening by the core-maker using personal sampler PT2. As this process is carried out using compressed air, it generates a lot of local dust which is collected by the personal sampler almost exclusively. If the clustering procedure is repeated without using the data generated by PT2, the resulting dendrogram, given in Fig. 5, yields at a dissimilarity level of 0.045 the three groups as obtained by comparing the contour plots with the elements Mg and Cr returned in the La- and the Fe-group respectively. It is interesting to also look for subgroups at a lower dissimilarity level in the dendrogram, for
23 TABLE 4 THE COMPOSITION (in ppm) OF F L O O R DUST, F A L L O U T DUST AND SOME RAW MATERIALS COLLECTED FROM THE F O U N D R Y (CW) Core-wash; (PI) pitch used in moulding; (MS) moulding sand; (SS) shake-out sand; (FD) floor dust from fettling shop; (PD) floor dust from pouring lines. Element Na Mg A1 C1 K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
OOC
002
CW
PI
890 15100 11100 2000 1420 400 3.86 26.0 1300 76 23700 38.1 65 19.0 5.0 1.4 0.10 20 4.3 10 0.36
9600 2700 6450 17800 270 6200 0.059 96 17.0 95 650 0.9 102 25 16 1.67 0.20 22 0.58 1.5 0.09
MS 2500 3000 15300 470 3530 2900 2.26 9.8 18.1 42 6600 1.94 30 0.24 3.1 0.36 0.89 140 9.1 18 0.13
FD 760 2000 7800 730 1200 1500 1.32 65 342 4550 611000 66 92 92 6.4 11.0 0.10 375 6.1 15.7 0.20
PD
SS
3100 3800 16800 900 4320 5500 2.53 39 115 1250 140000 17.5 262 27 5.1 4.4 0.92 800 9.5 20.4 0.28
1530 2300 9500 420 2200 2000 1.33 5.5 18.2 450 3780 1.09 0.3 0.34 2.7 0.05 0.50 91 5.7 11.5 0.15
Na Sc At Cs Eu K Ca ,'VIg La Ce V Co BQ Fe Cr Mn As Sb Zn Cl Br
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Fig. 5. Element clustering among time-averaged samples and fallout dust except for the sample from the fettling shop and personal sampler PT 2.
24 instance at 0.021. The elements As, Sb, Zn together with Mn, which were already found to be associated largely with submicrometer particles, are separated from the original Fe-group; the La-group also splits up into two subgroups. The one subgroup only contains La and Ce which are both added to the melt to produce nodular cast iron during 2 days (2 x 8 h) of the week. It is surprising that Eu, which is also added, does not belong to this subgroup. It can be concluded that this composition-fluctuation-pattern clustering routine yields very much the same, but more detailed information than do the concentration or composition contour plots.
Source identification Another approach to studying the impact of the different sources on the air quality in the different areas of the workshop is by comparing the composition of the dust at the sampling locations with the composition of some of the materials handled in the shop. The composition of a sample is in fact associated with the location of the sampling site, relative to the different sources which generate particles differing in chemical composition. For a set of samples taken from a network with many stations, the similarities or dissimilarities between sample compositions constitute useful information about the spread of pollutants from a single source, or several sources generating pollutants similar in composition and perhaps even the mixing of pollutants from different sources. On the other hand the dissimilarities between samples, or groups of similar samples, provide information about the number and locations of the sources. Because changes in emission rates, accidental events around a sampling site, and above all dispersion of the material in the room, are sources of random interferences for sample composition--source location relationships, a sophisticated classification method is needed. A computer program called DISSIM, developed by Op de Beeck {1977, 1980) was used for this purpose. A matrix of dissimilarities is constructed and by a clustering routine a dendrogram is produced. The data set used consisted of the sixteen time-averaged mean compositions for the sixteen indoor stations, together with the composition of the three personal samplers and the composition of a number of potential sources. The following seven samples were considered as potential sources. -- PI : A sample of pitch, which is used in the moulding sand. When the moulds are filled with h o t liquid metal, the pitch ignites and produces thick fumes. - - MS : Moulding sand. -- SS : The shake-out sand which is to be recycled for reuse as moulding sand after purification. --FD: Floor dust collected in the fettling shop, containing primarily grinded cast-iron. - - PD : Floor dust collected between the pouring lines. - - S F : T h e earlier mentioned fallout dust collected in the immediate vicinity of the shake-out machine. --CW: Core-wash applied as an alcoholic suspension onto the cores and
25 4 5-2 5-I 6
8 15 9
2 14 10 11 12 7
PT2PTI I PT3 SF MS SS PD PI cw 13 FD
°oi I 02I0
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Fig. 6. Clustering of time-averaged stationary and personal samples, fallout dust, floor dust and materials handled in the shop.
later on largely removed by evaporation in an oven or with compressed air. The results of these analyses are given in Table 4. The composition of the fallout dust has already been given in Table 3. The final result of the classification of these 26 samples in the form of a dendrogram is shown in Figure 6. If the dissimilarity level at 0.2 is considered, two groups of samples and three residual single samples can be distinguished. From this classification a number of conclusions can be drawn. - - T h e largest group consists of all air samples taken at the stationary stations, except the one from station 13 in the fettling shop, all personal samples, and SF, the fallout collected at the shake-out. This fallout is not a real "air sample" but can be considered as such, and was therefore used in the element-clustering classification; the composition of the particulate matter all over the workshop, except that from the fettling shop is thus rather similar, indicating that the shake-out process and the metal melting and pouring procedures are the most significant area-wide dust generators. - - T h e most intense source, namely the fettling procedure, does not represent a major contribution to the entire workshop. Because of their very large size, the particles generated by this process, ranging to almost mm-sized debris, have a very high fallout rate. Only the finer fraction ( < 5 pm} can be transported further than a few meters, but can no longer significantly alter the composition of the particulate matter at the other sampling stations. - - T h e floor dust generally does not reflect the composition of the airborne particles. The floor dust (FD) collected at the fettling shop is only at a high level of dissimilarity grouped with the air sample collected at that site (station 13}. - - T h e moulding sand (MS) and the shake-out sand (SS) are grouped together and at a slightly higher dissimilarity level related with the floor dust of the pouring (PD), but they are not similar to any air sample. The same is true for pitch (PI) and the core-wash material (CW).
26
When going into the finer details of the dendrogram, that is at lower dissimilarity levels, 0.08 and 0.06 for instance, the following conclusions seem obvious: -- The personal samples PTI, PT2 and PT3 are separated from the other air samples because of the specificity of the activities performed by the individual persons wearing these samplers. -- The group of samples from stations 10, 11, 12 and 17 is dominated b y the shake-out dust, b u t undergoes the influence of the nearby fettling process. The group of samples from stations 8, 15, 9, 2 and 14 is dominated by the shake-out dust. - - T h e samples from stations 4, 5-1, 5-2 and 6, situated in a relatively undisturbed area, are separated from the shake-out dominated group owing to settling of large particles during transport. - - T h e sample from station 3 is first separated from the large group of stationary samplers because it undergoes the influence of the ventilation through the open door. However, one should be cautious, not to go too far into the details of a dendrogram, because at very low dissimilarity levels small variations in composition and analysis errors may cause changes in grouping without real significance. -
-
CONCLUSIONS
In this investigation it was shown that instrumental neutron activation analysis can be a powerful tool in the study of the composition of industrial particulate matter. To reduce the wealth of data obtained when this technique is used for the analysis of a large number of samples from a network, several mathematical treatments were applied. To visualise the element distribution patterns over the area monitored, a computer program for contour plotting was found useful in both the concentration profile delineation and in the investigation of the dust composition. Both types of distribution patterns appeared to be strongly associated with the locations of the major emission sources. Also, computer operated classification or cluster methods revealed significant relations between elements in the foundry dust and were helpful in source identification. With the aid of these classification programs and the contour plots, a general idea of the impact of different sources on the overall levels of particulate levels of particulate pollution in the workshop could be obtained. Concentration and composition contour plots as well as cluster analysis indicated the presence of three main groups of elements, namely the La-group, the Fe-group and the Br-group. The La-group consists of lithophilic elements, Na, K, Mg, Ca, A1, Sc, Cs, La, Ce and Eu which are associated with coarse particles. They are primarily generated by the pouring procedure (slag-phase of molten iron), the
27
shake-out process and the moulding (sand, clay, lime, etc.}. These three sources contribute significantly to the overall air quality throughout the entire workshop. The Fe-group consists mainly of the siderophilic and chalcophilic elements V, Cr, Mn, Fe, Co, Zn, As, Sb and Ba. These are components of casting iron and are generated by the fettling and the shake-out process. The relatively volatile elements Mn, Zn, As and Sb are primarily associated with fine particles while the other members of this group are to be found on coarse particles. The shake-out process is the one source which has most likely the largest impact on the concentrations of these elements throughout the workshop. It is assumed that the particles with a high content of Fe-group elements are formed when molten iron is poured into the cold moulds, and that they are released when the moulds are shaken from the cast iron. The elements of the subgroup Mn, Zn, As and Sb are also significantly produced during melting and pouring by condensation of fumes and vapours, which accounts for their slightly different distribution pattern and their association with finer particles. The fettling process generates a large amount of very coarse fragments of cast iron, which accounts for the extremely steep element concentration gradients around the fettling shop. It is a very intense source for the Fe-group elements but has only a localized importance. Fine particles with high concentrations of Br and C1 are produced from burning pitch, and distributed nearly evenly over the workshop. Another localized source, namely the core-maker, was shown by concentration peaks for Mg and Cr, which are major components of the core-wash. Many of these conclusions were confirmed by the application of scanning electron microscopy to study the morphology of the particles and by X-ray analyses on single particles (Zhang, 1983). An important conclusion is that the composition of the foundry dust, except in the fettling shop and in the immediate vicinity of the core-maker, is relatively homogeneous throughout the workshop. This is probably due to internal air circulation in the room and the constancy of the composition of the generated dust. This conclusion implies that in order to monitor the composition of dust in this room the number of sampling stations may be reduced to three, located respectively in the fettling shop, shake-out department and core-making department. The close grouping of more than 20 elements in three groups suggests that data on three indicator elements may be sufficient to quantify the pollution levels, which would largely simplify the analytical procedure for routine studies. ACKNOWLEDGEMENTS
The authors gratefully acknowledge Dr J. Op de Beeck and Prof Dr J. Hoste for helpful advice and critical discussions on the data treatment. The authors are also indebted to Director W. Verhaege and Ir J. Verhaege and Ir P. Verhaege for their readiness to allow the experiments in their workshop. The cooperation of the workmen under the supervision of Ing Boterbergh is highly appreciated.
28 REFERENCES Dams, R., J.A. Robbins and J.W. Winchester, 1970. Neutron activation analysis of air pollution particulates. Anal. Chem., 42 (8): 861--867. Dams, R., G. Temmerman and M. Vanhoorne, 1972. Neutron activation analysis of smoke released during the production of nodular cast iron and the determination of possible effects on man. In: Nuclear Activation Techniques in the Life Sciences, Edit. IAEA Vienna, pp. 233--249. Dreisbach, L.H., 1974. Handbook of Poisoning, Lange Medical, Los Altos, CA, 8th edn. Friberg, L., G.F. Nordberg and V.B. Voulk (Eds.), 1979. Handbook of the Toxicology of Metals. Elsevier/North-Holland Biomedical Press, Amsterdam. Op de Beeck, J., 1977. Activation analysis: a basis for chemical classification. J. Radioanal. Chem., 37: 213--221. Op de Beeck, J., 1978. The Contor-Tridim program package. Internal Report, INWGHEM-4, University of Ghent, Belgium. Op de Beeck, J., 1980. Program packages DISSIM and HADCLU. Unpublished work, INW, University of Ghent, Belgium. Zhang, J., 1983. Sampling and analysis of particulate matter suspended in the workplace of an iron foundry. PhD Thesis, University of Ghent, Belgium. Zhang, J., J. Billiet and R. Dams, 1981. Stationary sampling and chemical analysis of suspended particulate matter in a workplace. Staub Reinhalt. Luft, 41 (10): 381--386. Zhang, J., J. Billiet, M. Nagels and R. Dams, 1983. Survey of total and respirable suspended particulate matter in an iron foundry. Comparison of stationary sampling and personal monitoring. Sci. Total Environ., 30: 167--180.
13
ELEMENTAL COMPOSITION AND SOURCE INVESTIGATION OF PARTICULATES SUSPENDED IN THE AIR OF AN IRON FOUNDRY
JIQIANG ZHANG, JEANNINE BILLIET and RICHARD DAMS
Institute for Nuclear Sciences, Rijksuniversiteit Gent, Proeftuinstraat 86, B-9000 Gent (Belgium) (Received April 10th, 1984 ; accepted June 9th, 1984) ABSTRACT
In the workshop of an iron foundry suspended particulate matter was daily collected with stationary filtration systems, Andersen cascade impactors and personal samplers. During a two-week period, with a network of sixteen stationary samplers and personal samplers carried by three workers active in the different departments of the workshop, a survey was made of the levels. Some samples were also taken of the major emission sources in the foundry. All samples were analysed by instrumental neutron activation analysis. Data were obtained for 21 elements in all samples, while 15 additional elements could only be detected in the large majority of the samples. F o r visualisation and interpretation of the data computer programs for contour plotting, classification and clustering of the elements and the samples were applied. The size distribution, the air concentration profile delineation and the element clusters indicated the presence of three main groups of elements. The La-group, consisting of lithophilic elements such as Na, K, Mg, Ca, Sc, La, Ce and Eu and associated with large particles, is primarily generated by the pouring, shake-out and moulding process. The Fe-group, with elements such as V, Cr, Mn, Fe, Co, Zn, As, Sb and Ba, originates primarily during fettling and shake-out. A few of these, Mn, Zn, As and Sb, are largely associated with fine particles. The elements Br and C1, which are produced from burning pitch, are nearly evenly distributed throughout the room. The results allow estimates of the impact of the major emission sources on the entire workroom, and of some localized sources in their immediate vicinity. Suggestions for representative sampling locations and indicator elements are obtained from the results.
INTRODUCTION A w o r k s h o p o f a n i r o n f o u n d r y is a m u l t i - s o u r c e a r e a o f p a r t i c u l a t e c o n t a m i n a n t s . O w i n g t o t h e v a r i e t y o f s o u r c e s in s u c h a n a r e a t h e n a t u r e o f p a r t i c u l a t e s s u s p e n d e d in t h e a i r v a r i e s c o n s i d e r a b l y . N o v a l i d a s s e s s m e n t o f the impact of the particulate contaminants on human health can be made without at least some knowledge of the chemical composition and the a e r o d y n a m i c p a r t i c l e size o f t h e c o n t a m i n a n t s . I n a p r e v i o u s p a p e r ( Z h a n g e t al., 1 9 8 1 ) t h e s a m p l i n g t e c h n i q u e s t o b e u s e d f o r t h e m e a s u r e m e n t o f t h e total and respirable suspended particulate matter were discussed. It was shown that after sample collection on Millipore membrane filters, or with 0048-9697/85/$03.30
© 1985 Elsevier Science Publishers B.V.
14 Andersen cascade impactors, instrumental neutron activation analysis allows the quantitative determination of approximately 30 elements in the particulate matter. A second paper (Zhang et al., 1983) described the levels of total and respirable particulate matter encountered in this workshop and the comparison of stationary and personal monitoring in three of the source areas. A number of interesting conclusions could be drawn from this study, based on the results of a sampling network consisting of 16 stationary sampling stations set up in the f o u n d r y and a few personal samplers carried by workers active in different areas of the shop. For respirable particles one to two well-situated stationary size-selective samplers can provide a good estimate of the personal exposure as measured with a personal respirable monitor. In the immediate vicinity of intense point sources of coarse particles, however, stationary sampling cannot be used to estimate the personal exposure to total suspended particulates. The survey of the particulate levels obtained by the network showed large variations in concentration gradients as a function of time. The aim of the present study is to identify the major particulate emission sources in the workshop and to evaluate their impact on the air quality of the entire room by chemical analysis and by measurement of the aerodynamic particle size of the dust collected at the different sampling sites. The distribution patterns of the different elements over the workshop can be visualised with a computer program for contour plotting; classification methods can also be used to group the elements according to their distributions. The composition of the dust collected at the different sampling sites can also provide some information on the impact of different emission sources on the overall levels of contaminants in the shop. Therefore a comparison must be made with the composition of the emission samples collected at the sources.
EXPERIMENTAL
Sampling site and equipment The sampling site, measuring 100 × 50 m was fully described in a previous paper (Zhang et al., 1983); only a scheme of the workshop and the position of the different sampling stations are given here, as illustrated in Fig. 1. Air from fourteen locations in the room, and one outdoor site {16), was sampled with 47 mm diameter membrane filters, pore size 3.0 pm, a t a flowrate of 0.8 m 3 h -1 . The filterholders are fixed at a height of 1.6 m and are oriented downwards. In addition, at three sites (namely 1, 5-1 and 14) the particles are classified according to their aerodynamic particle size with a nine-stage Andersen cascade impacter (ACI) operating at a flowrate of 1.7 m 3 h -1 . Personal total particulate samplers were carried during part of the two-weeklong sampling period by three workers active in the metal pouring- (PT 1), the core-making- (PT 2) and the shake-out departments (PT 3), respectively. In the metal melting and pouring department (A and B in Fig. 1) the molten
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metal is treated and transferred into the moulds positioned along the pouring lines. The core-making department (I in Fig. 1) is situated in a relatively quiet area of the workshop. Cores, specially formed parts of a mould used to form internal holes in a casting, are made by hand and sprayed or swabbed with "core wash" and baked. Afterwards they are cleaned with pressurised air. In the shake-out department the castings are shaken out of the moulds after they have solidified. This operation is performed by placing the flask containing the mould and casting on a vibrating grid called a "shake-out machine" (D in Fig. 1). The personal samplers consisted of a 37 mm lapel-type filterholder containing a membrane filter. The flowrate was constant at approximately 1.851 min -1 .
Chemical analysis After weighing at constant temperature and humidity (50% RH) the filters and the impaction sheets were pressed into pellets for instrumental neutron activation as described before (Dams et al., 1970). For some 20 elements the reproducibility of the analysis is generally better than 10%. When at least 5 mg dust is collected an additional 10--15 elements can mainly be detected with larger uncertainties. It was found (Zhang et al., 1981) that for a number of easily detected elements the overall reproducibility of the procedure is 7%, of which 5% can be attributed to the sampling.
Sampling period The study lasted 2 weeks (10 working days). To conform with the
16 TABLE 1 MEAN, MAXIMUM AND MINIMUM CONCENTRATIONS OF ELEMENTS (inpgm -3 ) MEASURED AT STATIONARY INDOOR AND OUTDOOR STATIONS Element
Na Mg A1 C1 K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
Geom. mean
41.2 81.5 260 7.6 43.2 88.9 0.040 0.43 0.96 15.0 590 0.13 4.5 0.52 0.12 0.15 0.016 8.40 0.15 0.30 0.0042
Concentration (pg m -3 ) Max. (station)
Min. (station)
107 (14) 184 (14) 1650 (13) 14 (13) 101 (14) 334 (13) 0.153 (13) 6.8 (13) 14.7 (13) 416 (13) 13600 (13) 2.5 (13) 44 (13) 9.6 (13) 0.21 (13) 1.6 (13) 0.038 (14) 171 (13) 0.51 (13) 2,2 (13) 0.0096 (14)
10.7 (3) 19.6 (3) 50 (3) 2.7 (14) 8.5 (3) 28.2 (3) 0.0094 (3) 0.088 (3) 0.20 (3) 6.1 (5-1) 120 (3) 0.029 (3) 2.0 (3) 0.17 (3) 0.09 (14) 0.07 (3) 0.005 (3) 2.3 (5-1) 0.044 (5-2) 0.076 (3) 0.0015 (3)
Outdoor (stat. 16) 0.59 0.23 0.48 0.57 0.38 0.62 0.0001 0.017 0.005 0.049 0.90 0.00077 0.13 0.0085 0.026 0.0077 0.00019 < 0.073 0.00046 0.00075 <:0.00013
w o r k i n g h o u r s a sampling time o f 8 h was c h o s e n and the filters were c h a n g e d daily. O w i n g t o s o m e incidents a few samples are missing so t h a t the n u m b e r o f sampling days varies b e t w e e n 6 and 9. Also the special studies p e r f o r m e d with t h e cascade i m p a c t o r s and the personal samplers lasted o n l y for 2--5 days. T h e d a y - b y - d a y variations o f the c o n c e n t r a t i o n s in t h e air were t y p i c a l l y a f a c t o r o f 2.5, b u t will n o t be discussed in the present paper. Instead a time-averaged m e a n c o n c e n t r a t i o n was calculated f o r all stations. The m e a n values o b t a i n e d for t o t a l s u s p e n d e d particulates varied f r o m a low o f 1 . 3 6 m g m -3 at station 3 t o a high o f 5 1 . 9 m g m -3 at s t a t i o n 13, while t h e m e a n value at the o u t d o o r s t a t i o n 16 was o n l y 0 . 0 3 3 mg m -3 .
RESULTS AND DISCUSSION
Distribution patterns of the elements In Table 1 t h e g e o m e t r i c m e a n values o f the time-averaged c o n c e n t r a t i o n s for 21 elements in t h e air at all sixteen i n d o o r s t a t i o n a r y stations are given. F r o m the c o m p a r i s o n with the c o n c e n t r a t i o n s at t h e o u t d o o r station 16 it is
17 TABLE 2 M A X I M U M A N D MINIMUM C O N C E N T R A T I O N S (in p g m -3) M E A S U R E D A T S T A T I O N A R Y I N D O O R A N D O U T D O O R S T A T I O N S F O R E L E M E N T S WHICH A R E NOT D E T E C T E D IN E V E R Y SAMPLE (--: below limit of detection) Element
Ti Ni Cu Ga Se
Concentration (pg m -3 ) Max. (station)
Min. (station)
O u t d o o r s (stat. 16)
36 (12) 18 (13) 42 (13) 3.8 (12) 0.054(13)
1.6 0.32 0.51 0.025 0.008
0.032 -0.019 0.002
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0.63
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0.006
(6)
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0.031 0.79 0.013 0.18 0.11 0.022 0.37 0.003 0.41
(4) (13) (12) (2) (12) (13) (13) (13) (13)
0.008 0.014 0.0008 0.010 0.003 0.0009 0.010 0.0001 0.016
(5-2) (1) (4) (5-1) (6) (4) (6) (9) (5-1)
--
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clear that intense emission sources exist for all these elements. To give an idea of the variations the maximum and minimum time-averaged concentrations are given in Table 1. At station 13, at the fettling shop, almost all elements have their peak concentration. In this shop the final refinement of the castings called "finishing" or "fettling" is carried out. The workers remove gates, risers and surface imperfections of the castings by sledge° hammers, friction saws and grinding wheels. Grinding produces rather large fragments of metal and blows a lot of dust into the surrounding air; therefore the fettling shop is the most dusty area of the workroom. The lowest concentrations are found at station 3, which is strongly influenced by the natural convection from a door, and at stations 5-1 and 5-2 in the relatively calm area of the core-making department. Fifteen other elements were detected in a number of samples, but their concentrations often approached the limit of detection of the method. In Table 2 the maximum and minimum values measured are summarised, together with the concentrations measured at o u t d o o r station 16. It is clear that these elements have sources in the workroom; a discussion of these 15 elements will n o t be considered further. Although it is clear from Tables 1 and 2 that the values for all elements largely exceed the o u t d o o r values, they do not approach the Threshold Limit Values (TLV) as established today, with the exception of Fe (Dreisbach, 1974). In the fettling shop the TLV of 1 mg m -3 for Fe is
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19 largely exceeded which is not without hazard as while siderosis is a known effect on the lungs following high exposure to Fe, there is also an increased risk of lung cancer as reported by Friberg et al. {1979). Based on the time-averaged concentrations in the air at all sixteen stations, intermediate concentrations are calculated with a computer program called Contor-Tridim (Op de Beeck, 1978). To visualise the distribution pattern for all 21 elements isoconcentration lines are drawn in a contour diagram. These plots enable us to evaluate the size of different source-areas, and to divide the elements into groups with similar distributions. Three groups could be identified, and for each a representative plot is shown in Fig. 2. The distribution of La is characteristic for a large group of elements, namely Na, K, Cs, Mg, Ca, A1, Sc, La, Ce and Eu. These elements have a major concentration peak in the fettling shop, and a minor one in the pouring department. The distribution of Fe is indicative for a group with V, Cr, Mn, Fe, Co, Zn, Ba, As and Sb with a very sharp peak in the fettling shop. The group of volatile elements consists only of Br and C1 and concentration variations for these elements are very smooth. Element distribution as a function o f particle size An Anderson Cascade Impactor was used to classify the particles as a function of their "aerodynamic diameter" in the pouring, core-making and shake-out departments. The impactor collects the particles in nine different fractions on eight different stages and a back-up filter. Owing to the mechanical construction of the multistage impactor, fifty percent of the mass of the particles collected on stage 0 has an aerodynamic diameter of > 11 pm; fifty percent of the masses of the particles collected on stages 1--7 have aerodynamic diameters of 7.8, 4.7, 3.3, 2.1, 1.1, 0.65 and 0.43, respectively, while particles with smaller aerodynamic diameters are collected by the back-up filter. This allows the construction of size distribution curves as illustrated in Fig. 3, for all elements chemically determined in the collected particles, and also provides an indication of the association of the elements with different particle sizes. At all three locations of the experiment, the elements Na, Mg, A1, K, Ca, Sc, Cr, Fe, Co, Cs, Ba, La, Ce and Eu are shown to be associated exclusively with the "coarser" particles, as illustrated by the size--weight curves of Fe in Fig. 3. Very similar curves were also found for the total of all particles suspended in the foundry (Zhang et al., 1983). Elements such as V, Zn, As and Sb show some association with "coarser" particles, but also with "smaller" particles, indicating that these elements are emitted, at least in part, as volatile compounds. As an illustration, the size--weight curves of the element As is given in Fig. 3. Volatile elements such as C1 and Br are found to be primarily associated with "small" particles in the pouring- and core-making department, but also show to some extent an association with "coarser" particles in the shake-out department (see Fig. 3). The same applies for the element V (not illustrated). An explanation may be that during the shake-out process particles are
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0....0..~
/
...~..-4....~2
~O.;
"
I
O.5
..010
OO2
0.1 Cul-off
? 6 5 4 3 2 Filter
I
OStage
I
0 43 0 651 1 211 3 3 4 7 7 0 I I I I . l I
Rlter
7 6 5 4 3 2 I
111
0Stage
Fig. 3. Size distribution curves for Fe, As and Br in: (I) pouring department; (II) coremaking department; (III) shake-out department and distribution curve for Mn in (IV-l) pouring department; (IV-2) core-making department and (IV-3) shake-out department.
released that are the result of solid--gaseous reactions. That part of the Mn emission in the foundry may take the form of volatile compounds is illustrated in Fig. 3, showing an association of Mn with small particles in the pouring- and core-making department. Morphological studies using a scanning electron microscope (Zhang, 1983) showed that Mn in fact relates with both coarse and fine particles. A similar distribution for Mn was also found in another foundry {Dams et al., 1972).
Composition of foundry dust With the total weight of each sample known, the results can also be expressed in terms of the concentration of the elements in the particulate
21 TABLE 3 MEAN CONCENTRATIONS (in ppm) OF SAMPLES COLLECTED WITH INDOOR STATIONARY AND PERSONAL SAMPLERS AND OF FALLOUT DUST
Element
Stationary stations Geom. mean
Na Mg A1 CI K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
7700 16900 48100 1600 8400 18500 7.2 74 170 2990 108000 24 830 95 23 26 3.0 1520 27 54 0.72
Personal samplers
Max. (station) 10300 23200 66700 5900 11300 27500 9.3 163 297 8880 263000 49 1520 172 79 48 4.35 3320 51 93 1.2
(i) (1) (I) (3) (5-2) (1) (1) (13) (5-1) (13) (13) (3) (13) (3) (3) (1) (13) (1) (1) (1)
Min. (station) PT 1
PT 2
3960 ( 1 3 ) 9000 (13) 31900(13) 268 ( 1 3 ) 1850 (13) 6400 (13) 2.9 (13) 54 (2) 95 (1) 1720 (1) 37800 (1) 13 (1) 570 (14) 42 (1) 4.1 (13) 17 (15) 0.45 (13) 930 (2) 9.8 (13) 29 (12) 0.53 (5-1)
4 5 0 0 10200 59000 19000 30000 66000 2800 760 -1120 15000 23000 6.0 9.8 50 57 585 126 2100 1000 77000 70000 36 16 820 370 120 36 23 36 23 8 2.0 3.7 1.1 0.97 21 38 44 80 0.48 0.95
9700 22000 61000 3600 1160 26000 8.3 62 194 3300 66000 19 1100 70 39 28 4.0 1.1 98 150 1.3
SF
PT 3 10700 17000 44000 1140 12100 12000 9.6 35 82 580 46200 10.6 190 9.6 8.0 25 3.6 510 34 71 0.97
matter. Since in the different areas of the workshop the same activities are repeated all year round, it may be assumed that each stationary sampler collects dust with a typical composition which is largely determined by the neighbouring emission sources. Of all the samples taken at the different sites of the workshop, but excluding those taken by personal samplers, the mean composition was calculated based on daily samples. From these mean compositions a general geometric mean composition for the whole workshop is given in Table 3, together with the m a x i m u m and the minimum values. In order to provide a mathematical basis for the grouping of the elements an element clustering program was applied to the (16 x 21) data set. The classification is carried out with the aid of a computer program, named HADCLU, developed by Op de Beeck {1977, 1980). For an explanation of the clustering strategy and the algorithms and formulae used, the reader is referred to the original publications. The program allows a graphical representation of the clustered data in the form of a dendrogram as illustrated by Fig. 4. All elements are placed equidistant (by choice) on the top. Vertical distances indicate "dissimilarities" between elements as calculated by the computer program. They have no absolute
22 No Sc AI Cs Eu K Ca La Ce V Co Ba Fe Mn As Sb Zn M
OOOoo
Cr Cl Br
00/,
0.06
[
O.OB
010
Fig. 4. Element clustering among time-averaged samples and fallout dust except for the
sample from the fettling shop. meaning and should only be compared within a single classification. Groups of elements, called clusters, can be identified as showing "large" dissimilatities as compared to the "small" dissimilarities between the elements of a single group. For the element classification of the foundry dust, the calculation was carried out using the mean composition of all samples taken at the different stations in the foundry except the samples from station 13. The fettling procedure carried out at this station must be considered as a source of only local importance in view of the very large size of the emitted particles, The composition of the fallout dust collected on t o p of protecting casework of some machinery in the vicinity of the largest shake-out machine of the workshop as given in Table 3 (SF), and the composition of the personal samples in Table 3 (PT1, PT2, PT3 ) are also included in the data; the resulting dendrogram is given in Fig. 4. Examination of the dendrogram at a dissimilarity level of 0.045, shows that four groups of elements can be distinguished corresponding to the earlier defined La, Fe and Br groups, except for the somewhat surprising group of the elements Mg and Cr. Analyses of the different sources in the room (see section source identification and Table 4) later showed that the core-wash used in the core-making shop also contains large amounts of Cr and Mg. This core-wash is spread onto the cores and then removed after hardening by the core-maker using personal sampler PT2. As this process is carried out using compressed air, it generates a lot of local dust which is collected by the personal sampler almost exclusively. If the clustering procedure is repeated without using the data generated by PT2, the resulting dendrogram, given in Fig. 5, yields at a dissimilarity level of 0.045 the three groups as obtained by comparing the contour plots with the elements Mg and Cr returned in the La- and the Fe-group respectively. It is interesting to also look for subgroups at a lower dissimilarity level in the dendrogram, for
23 TABLE 4 THE COMPOSITION (in ppm) OF F L O O R DUST, F A L L O U T DUST AND SOME RAW MATERIALS COLLECTED FROM THE F O U N D R Y (CW) Core-wash; (PI) pitch used in moulding; (MS) moulding sand; (SS) shake-out sand; (FD) floor dust from fettling shop; (PD) floor dust from pouring lines. Element Na Mg A1 C1 K Ca Sc V Cr Mn Fe Co Zn As Br Sb Cs Ba La Ce Eu
OOC
002
CW
PI
890 15100 11100 2000 1420 400 3.86 26.0 1300 76 23700 38.1 65 19.0 5.0 1.4 0.10 20 4.3 10 0.36
9600 2700 6450 17800 270 6200 0.059 96 17.0 95 650 0.9 102 25 16 1.67 0.20 22 0.58 1.5 0.09
MS 2500 3000 15300 470 3530 2900 2.26 9.8 18.1 42 6600 1.94 30 0.24 3.1 0.36 0.89 140 9.1 18 0.13
FD 760 2000 7800 730 1200 1500 1.32 65 342 4550 611000 66 92 92 6.4 11.0 0.10 375 6.1 15.7 0.20
PD
SS
3100 3800 16800 900 4320 5500 2.53 39 115 1250 140000 17.5 262 27 5.1 4.4 0.92 800 9.5 20.4 0.28
1530 2300 9500 420 2200 2000 1.33 5.5 18.2 450 3780 1.09 0.3 0.34 2.7 0.05 0.50 91 5.7 11.5 0.15
Na Sc At Cs Eu K Ca ,'VIg La Ce V Co BQ Fe Cr Mn As Sb Zn Cl Br
"-',='-r~ '
~-,-~ 1'
I
004
006
008
0.10
Fig. 5. Element clustering among time-averaged samples and fallout dust except for the sample from the fettling shop and personal sampler PT 2.
24 instance at 0.021. The elements As, Sb, Zn together with Mn, which were already found to be associated largely with submicrometer particles, are separated from the original Fe-group; the La-group also splits up into two subgroups. The one subgroup only contains La and Ce which are both added to the melt to produce nodular cast iron during 2 days (2 x 8 h) of the week. It is surprising that Eu, which is also added, does not belong to this subgroup. It can be concluded that this composition-fluctuation-pattern clustering routine yields very much the same, but more detailed information than do the concentration or composition contour plots.
Source identification Another approach to studying the impact of the different sources on the air quality in the different areas of the workshop is by comparing the composition of the dust at the sampling locations with the composition of some of the materials handled in the shop. The composition of a sample is in fact associated with the location of the sampling site, relative to the different sources which generate particles differing in chemical composition. For a set of samples taken from a network with many stations, the similarities or dissimilarities between sample compositions constitute useful information about the spread of pollutants from a single source, or several sources generating pollutants similar in composition and perhaps even the mixing of pollutants from different sources. On the other hand the dissimilarities between samples, or groups of similar samples, provide information about the number and locations of the sources. Because changes in emission rates, accidental events around a sampling site, and above all dispersion of the material in the room, are sources of random interferences for sample composition--source location relationships, a sophisticated classification method is needed. A computer program called DISSIM, developed by Op de Beeck {1977, 1980) was used for this purpose. A matrix of dissimilarities is constructed and by a clustering routine a dendrogram is produced. The data set used consisted of the sixteen time-averaged mean compositions for the sixteen indoor stations, together with the composition of the three personal samplers and the composition of a number of potential sources. The following seven samples were considered as potential sources. -- PI : A sample of pitch, which is used in the moulding sand. When the moulds are filled with h o t liquid metal, the pitch ignites and produces thick fumes. - - MS : Moulding sand. -- SS : The shake-out sand which is to be recycled for reuse as moulding sand after purification. --FD: Floor dust collected in the fettling shop, containing primarily grinded cast-iron. - - PD : Floor dust collected between the pouring lines. - - S F : T h e earlier mentioned fallout dust collected in the immediate vicinity of the shake-out machine. --CW: Core-wash applied as an alcoholic suspension onto the cores and
25 4 5-2 5-I 6
8 15 9
2 14 10 11 12 7
PT2PTI I PT3 SF MS SS PD PI cw 13 FD
°oi I 02I0
030[
Fig. 6. Clustering of time-averaged stationary and personal samples, fallout dust, floor dust and materials handled in the shop.
later on largely removed by evaporation in an oven or with compressed air. The results of these analyses are given in Table 4. The composition of the fallout dust has already been given in Table 3. The final result of the classification of these 26 samples in the form of a dendrogram is shown in Figure 6. If the dissimilarity level at 0.2 is considered, two groups of samples and three residual single samples can be distinguished. From this classification a number of conclusions can be drawn. - - T h e largest group consists of all air samples taken at the stationary stations, except the one from station 13 in the fettling shop, all personal samples, and SF, the fallout collected at the shake-out. This fallout is not a real "air sample" but can be considered as such, and was therefore used in the element-clustering classification; the composition of the particulate matter all over the workshop, except that from the fettling shop is thus rather similar, indicating that the shake-out process and the metal melting and pouring procedures are the most significant area-wide dust generators. - - T h e most intense source, namely the fettling procedure, does not represent a major contribution to the entire workshop. Because of their very large size, the particles generated by this process, ranging to almost mm-sized debris, have a very high fallout rate. Only the finer fraction ( < 5 pm} can be transported further than a few meters, but can no longer significantly alter the composition of the particulate matter at the other sampling stations. - - T h e floor dust generally does not reflect the composition of the airborne particles. The floor dust (FD) collected at the fettling shop is only at a high level of dissimilarity grouped with the air sample collected at that site (station 13}. - - T h e moulding sand (MS) and the shake-out sand (SS) are grouped together and at a slightly higher dissimilarity level related with the floor dust of the pouring (PD), but they are not similar to any air sample. The same is true for pitch (PI) and the core-wash material (CW).
26
When going into the finer details of the dendrogram, that is at lower dissimilarity levels, 0.08 and 0.06 for instance, the following conclusions seem obvious: -- The personal samples PTI, PT2 and PT3 are separated from the other air samples because of the specificity of the activities performed by the individual persons wearing these samplers. -- The group of samples from stations 10, 11, 12 and 17 is dominated b y the shake-out dust, b u t undergoes the influence of the nearby fettling process. The group of samples from stations 8, 15, 9, 2 and 14 is dominated by the shake-out dust. - - T h e samples from stations 4, 5-1, 5-2 and 6, situated in a relatively undisturbed area, are separated from the shake-out dominated group owing to settling of large particles during transport. - - T h e sample from station 3 is first separated from the large group of stationary samplers because it undergoes the influence of the ventilation through the open door. However, one should be cautious, not to go too far into the details of a dendrogram, because at very low dissimilarity levels small variations in composition and analysis errors may cause changes in grouping without real significance. -
-
CONCLUSIONS
In this investigation it was shown that instrumental neutron activation analysis can be a powerful tool in the study of the composition of industrial particulate matter. To reduce the wealth of data obtained when this technique is used for the analysis of a large number of samples from a network, several mathematical treatments were applied. To visualise the element distribution patterns over the area monitored, a computer program for contour plotting was found useful in both the concentration profile delineation and in the investigation of the dust composition. Both types of distribution patterns appeared to be strongly associated with the locations of the major emission sources. Also, computer operated classification or cluster methods revealed significant relations between elements in the foundry dust and were helpful in source identification. With the aid of these classification programs and the contour plots, a general idea of the impact of different sources on the overall levels of particulate levels of particulate pollution in the workshop could be obtained. Concentration and composition contour plots as well as cluster analysis indicated the presence of three main groups of elements, namely the La-group, the Fe-group and the Br-group. The La-group consists of lithophilic elements, Na, K, Mg, Ca, A1, Sc, Cs, La, Ce and Eu which are associated with coarse particles. They are primarily generated by the pouring procedure (slag-phase of molten iron), the
27
shake-out process and the moulding (sand, clay, lime, etc.}. These three sources contribute significantly to the overall air quality throughout the entire workshop. The Fe-group consists mainly of the siderophilic and chalcophilic elements V, Cr, Mn, Fe, Co, Zn, As, Sb and Ba. These are components of casting iron and are generated by the fettling and the shake-out process. The relatively volatile elements Mn, Zn, As and Sb are primarily associated with fine particles while the other members of this group are to be found on coarse particles. The shake-out process is the one source which has most likely the largest impact on the concentrations of these elements throughout the workshop. It is assumed that the particles with a high content of Fe-group elements are formed when molten iron is poured into the cold moulds, and that they are released when the moulds are shaken from the cast iron. The elements of the subgroup Mn, Zn, As and Sb are also significantly produced during melting and pouring by condensation of fumes and vapours, which accounts for their slightly different distribution pattern and their association with finer particles. The fettling process generates a large amount of very coarse fragments of cast iron, which accounts for the extremely steep element concentration gradients around the fettling shop. It is a very intense source for the Fe-group elements but has only a localized importance. Fine particles with high concentrations of Br and C1 are produced from burning pitch, and distributed nearly evenly over the workshop. Another localized source, namely the core-maker, was shown by concentration peaks for Mg and Cr, which are major components of the core-wash. Many of these conclusions were confirmed by the application of scanning electron microscopy to study the morphology of the particles and by X-ray analyses on single particles (Zhang, 1983). An important conclusion is that the composition of the foundry dust, except in the fettling shop and in the immediate vicinity of the core-maker, is relatively homogeneous throughout the workshop. This is probably due to internal air circulation in the room and the constancy of the composition of the generated dust. This conclusion implies that in order to monitor the composition of dust in this room the number of sampling stations may be reduced to three, located respectively in the fettling shop, shake-out department and core-making department. The close grouping of more than 20 elements in three groups suggests that data on three indicator elements may be sufficient to quantify the pollution levels, which would largely simplify the analytical procedure for routine studies. ACKNOWLEDGEMENTS
The authors gratefully acknowledge Dr J. Op de Beeck and Prof Dr J. Hoste for helpful advice and critical discussions on the data treatment. The authors are also indebted to Director W. Verhaege and Ir J. Verhaege and Ir P. Verhaege for their readiness to allow the experiments in their workshop. The cooperation of the workmen under the supervision of Ing Boterbergh is highly appreciated.
28 REFERENCES Dams, R., J.A. Robbins and J.W. Winchester, 1970. Neutron activation analysis of air pollution particulates. Anal. Chem., 42 (8): 861--867. Dams, R., G. Temmerman and M. Vanhoorne, 1972. Neutron activation analysis of smoke released during the production of nodular cast iron and the determination of possible effects on man. In: Nuclear Activation Techniques in the Life Sciences, Edit. IAEA Vienna, pp. 233--249. Dreisbach, L.H., 1974. Handbook of Poisoning, Lange Medical, Los Altos, CA, 8th edn. Friberg, L., G.F. Nordberg and V.B. Voulk (Eds.), 1979. Handbook of the Toxicology of Metals. Elsevier/North-Holland Biomedical Press, Amsterdam. Op de Beeck, J., 1977. Activation analysis: a basis for chemical classification. J. Radioanal. Chem., 37: 213--221. Op de Beeck, J., 1978. The Contor-Tridim program package. Internal Report, INWGHEM-4, University of Ghent, Belgium. Op de Beeck, J., 1980. Program packages DISSIM and HADCLU. Unpublished work, INW, University of Ghent, Belgium. Zhang, J., 1983. Sampling and analysis of particulate matter suspended in the workplace of an iron foundry. PhD Thesis, University of Ghent, Belgium. Zhang, J., J. Billiet and R. Dams, 1981. Stationary sampling and chemical analysis of suspended particulate matter in a workplace. Staub Reinhalt. Luft, 41 (10): 381--386. Zhang, J., J. Billiet, M. Nagels and R. Dams, 1983. Survey of total and respirable suspended particulate matter in an iron foundry. Comparison of stationary sampling and personal monitoring. Sci. Total Environ., 30: 167--180.