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Toxicity determination of quartz and coal mine dust by thermoluminescence
Nuclear Instruments and Methods 175 (1980) 239-240 © North-Holland Publishing Company
TOXICITY DETERMINATION OF QUARTZ AND COAL MINE DUST BY THERMOLUMINESCENCE Wilhelm KRIEGSEIS and Arthur SCHARMANN L Physikalisches lnstitut der Justus-Liebig-Universitdt, 63 Giessen, FRG
A novel application potential of thermoluminescence for the determination of the fibrogenic properties of quartz and coal mine dust is described.
The long-term inhalation of respirable silica dust causes a pulmonary disease called silicosis. In the case of low quartz levels the more general expression pneumoconiosis is used. This illness is one of the major health hazards in several industries, particularly in coal mining, where a complete suppression of dust exposures cannot be achieved. From laboratory investigations and epidemiological studies it is well known that the toxicity of mineral and coal mine dusts varies considerably. Therefore there is a need for dust safety standards which take these differences of the pathogenic behaviour into account. Such standards can only be established if a reliable routine method is available based on the measurement of a physical, chemical or mineralogical parameter which is closely related to the toxicity of the dusts. Up to now such a method did not exist. Although quartz is the most fibrogenic component of coal mine dust epidemiological investigations did not reveal any indications for a correspondence of the pneumoconiosis risk to the quartz content [1 ]. According to the results of ESCA (electron spectroscopy for chemical analysis) and scanning Auger surface investigations this discrepancy is caused by a non-uniform surface cleanliness of quartz due to other mineral or organic components of the coal [2,3]. Since only quartz surfaces but not the bulk of quartz grains take part in pathogenic interactions it is desirable to determine the portion of such uncontaminated surfaces. In principle mineralogical microscopy methods or surface analysis techniques of high lateral resolution like the scanning Auger spectroscopy are suitable for this purpose. Another method which is simple in comparison and therefore promising for routine applications has been derived from the thermoluminescence (TL) of dusts below room temperature [4]. Irradiated dust samples of natural quartz exhibit
characteristic TL-maxima at 165 and 250 K (fig. 1, curve a). These have been controversially interpreted so far. All authors have agreed, however, in the assumption of a bulk emission [5-8]. We consider this thermoluminescence to be surface specific and for that reason applicable to an estimation of the number of uncovered quartz surfaces. According to our results it can be attributed to defects at the boundary between the quartz surface and absorbed species containing OH-groups, for instance water. This assumption and the toxicity determinations are based on the following observations: (a) the intensity of the 165K TL-maximum increases by a factor of more than 10, and the intensity at 250 K by a factor of 2 - 3 if toxic quartz dust is wetted by water. After water desorption the thermoluminescence is rather weak. (b) ESCA investigations into biologically tested samples showed that less toxic quartz dusts are surface contaminated and do not exhibit this water induced increase of the TL4ntensity. (c) At a higher extent of surface covering the toxi12 ~1o in
8
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6
Z
0 100
200
300 Z,00 TEMPERATURE (K)
500
600
Fig. 1. TL of two respirable dust samples, (a) 86% quartz, (b) 49% quartz. 239
XIII. OTHER APPLICATIONS
240
W. Kriegseis, A. Scharmann / Toxicity determination
city is reduced even more, and the shape of the glow curve is altered. An example is given by curve b of fig. 1. (d) In both cases (b) and (c) the removal of surface coverings by a treatment with hot hydrochloric acid, which has been controlled by Auger spectroscopy, causes an increase of the toxicity and a more pronounced effect of the absorbed water on thermoluminescence. (e) Higher TL-intensity can be achieved not only by water but also by aliphatic alcohols, especially by methanol, whereas aromatic compounds or simple hydrocarbons like pentane or hexane behave neutrally. (f) The TL-curve shape of ice is similar to that of quartz dust although being much weaker. For toxicity determinations the absolute TL intensity at 165 K, its relative increase after water interaction and the TL-curve shape are taken as criteria. Other minerals like carbonates, mica, clay minerals, feldspars, hydrates or oxides of iron, magnesium or aluminium which occur together with quartz have a completely different and much weaker thermoluminescence and do not disturb the analysis. Our TL measurements are performed in a high vacuum apparatus which has been constructed by Robock [9]. 1 0 - 1 5 mg dust are sedimented by means of water free benzene, cooled down to liquid air temperature, irradiated by 30 kV X-rays through a beryllium window and heated. Subsequently the sample is wetted with water at room temperature and after pumping off the cycle is repeated once more. The X-ray exposures vary depending on the nature of the dusts. For quartz samples 9 X 10 -2 C/kg are sufficient to produce a maximum pulse rate which exceeds the background by a factor of 1000. For coal dust samples an exposure of 11 C/kg is generally used. The efficiency of the method can be seen from fig. 2 where cytotoxicity results of a biological in-vitro cell test are compared with a TL-estimation of toxicity for 50 dust samples. These originated from different sands and stones used in foundries, which have been investigated with respect to their silicosis risk by a cooperative research project between several institutions. Presently the TL-method is used in tests for coal mine dust in a modified manner. Since coal can hardly be wetted by water methanol is used. The first preliminary results from 25 samples of air-borne dust agreed fairly well with epidemiological data. It turned out that even at a
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Fig. 2. C y t o t o x i c i t y (a) and TL-estimation o f t o x i c i t y (b) o f
50 respirabte dust samples: (a) determined by K. Robock at the Institut f. Hygiene und Arbeitsmedizin, Gesamthochschule Essen by measuring the TTC-reduction activity of peritoneal macrophages of guinea pigs after dust incubation for 2 h (for details of the test see [9]). 100% means inert behaviour. The toxicity increases with declining ordinate values. (b) wt = weak toxicity or inert, mt = medium toxicity, ht = high toxicity, vht = very high toxicity.
quartz content of only 0.09% the typical TL-curve of quartz can be obtained.
References [1 ] M.T.R. Reisner, Gliickauf 113 (1977) 21. [2] W. Kriegseis, A. Scharmann and J. Serafin, Ergebn. v. Untersuchungen a.d.G.d. Staub- u. Silikosebek'~mpfung im Steinkohlenbergbau 12 (1979) 149. [3] W. Kriegseis, A. Scharmann and A. Joshi, ibid. 12 (1979) 159. [4] W. Kriegseis, A. Scharmann and J. Serafin, ibid. 11 (1977) 125. [5] W.L. Medlin, J. Chem. Phys. 38 (1963) 1132. [6] M. Schlesinger, J. Phys. Chem. Solids 26 (1965) 1761. [7] A. Halperin, A.A. Braner and J. Shapira, J. Luminescence 1 (1970) 385. [8] P.L. Mattern, K. Lengweiler and P.W. Levy, Rad. Eft. 26 (1975) 237. [9] K. Robock, Beitr. Silikose-Forsch. 26 (1974) 111.
TOXICITY DETERMINATION OF QUARTZ AND COAL MINE DUST BY THERMOLUMINESCENCE Wilhelm KRIEGSEIS and Arthur SCHARMANN L Physikalisches lnstitut der Justus-Liebig-Universitdt, 63 Giessen, FRG
A novel application potential of thermoluminescence for the determination of the fibrogenic properties of quartz and coal mine dust is described.
The long-term inhalation of respirable silica dust causes a pulmonary disease called silicosis. In the case of low quartz levels the more general expression pneumoconiosis is used. This illness is one of the major health hazards in several industries, particularly in coal mining, where a complete suppression of dust exposures cannot be achieved. From laboratory investigations and epidemiological studies it is well known that the toxicity of mineral and coal mine dusts varies considerably. Therefore there is a need for dust safety standards which take these differences of the pathogenic behaviour into account. Such standards can only be established if a reliable routine method is available based on the measurement of a physical, chemical or mineralogical parameter which is closely related to the toxicity of the dusts. Up to now such a method did not exist. Although quartz is the most fibrogenic component of coal mine dust epidemiological investigations did not reveal any indications for a correspondence of the pneumoconiosis risk to the quartz content [1 ]. According to the results of ESCA (electron spectroscopy for chemical analysis) and scanning Auger surface investigations this discrepancy is caused by a non-uniform surface cleanliness of quartz due to other mineral or organic components of the coal [2,3]. Since only quartz surfaces but not the bulk of quartz grains take part in pathogenic interactions it is desirable to determine the portion of such uncontaminated surfaces. In principle mineralogical microscopy methods or surface analysis techniques of high lateral resolution like the scanning Auger spectroscopy are suitable for this purpose. Another method which is simple in comparison and therefore promising for routine applications has been derived from the thermoluminescence (TL) of dusts below room temperature [4]. Irradiated dust samples of natural quartz exhibit
characteristic TL-maxima at 165 and 250 K (fig. 1, curve a). These have been controversially interpreted so far. All authors have agreed, however, in the assumption of a bulk emission [5-8]. We consider this thermoluminescence to be surface specific and for that reason applicable to an estimation of the number of uncovered quartz surfaces. According to our results it can be attributed to defects at the boundary between the quartz surface and absorbed species containing OH-groups, for instance water. This assumption and the toxicity determinations are based on the following observations: (a) the intensity of the 165K TL-maximum increases by a factor of more than 10, and the intensity at 250 K by a factor of 2 - 3 if toxic quartz dust is wetted by water. After water desorption the thermoluminescence is rather weak. (b) ESCA investigations into biologically tested samples showed that less toxic quartz dusts are surface contaminated and do not exhibit this water induced increase of the TL4ntensity. (c) At a higher extent of surface covering the toxi12 ~1o in
8
o
6
Z
0 100
200
300 Z,00 TEMPERATURE (K)
500
600
Fig. 1. TL of two respirable dust samples, (a) 86% quartz, (b) 49% quartz. 239
XIII. OTHER APPLICATIONS
240
W. Kriegseis, A. Scharmann / Toxicity determination
city is reduced even more, and the shape of the glow curve is altered. An example is given by curve b of fig. 1. (d) In both cases (b) and (c) the removal of surface coverings by a treatment with hot hydrochloric acid, which has been controlled by Auger spectroscopy, causes an increase of the toxicity and a more pronounced effect of the absorbed water on thermoluminescence. (e) Higher TL-intensity can be achieved not only by water but also by aliphatic alcohols, especially by methanol, whereas aromatic compounds or simple hydrocarbons like pentane or hexane behave neutrally. (f) The TL-curve shape of ice is similar to that of quartz dust although being much weaker. For toxicity determinations the absolute TL intensity at 165 K, its relative increase after water interaction and the TL-curve shape are taken as criteria. Other minerals like carbonates, mica, clay minerals, feldspars, hydrates or oxides of iron, magnesium or aluminium which occur together with quartz have a completely different and much weaker thermoluminescence and do not disturb the analysis. Our TL measurements are performed in a high vacuum apparatus which has been constructed by Robock [9]. 1 0 - 1 5 mg dust are sedimented by means of water free benzene, cooled down to liquid air temperature, irradiated by 30 kV X-rays through a beryllium window and heated. Subsequently the sample is wetted with water at room temperature and after pumping off the cycle is repeated once more. The X-ray exposures vary depending on the nature of the dusts. For quartz samples 9 X 10 -2 C/kg are sufficient to produce a maximum pulse rate which exceeds the background by a factor of 1000. For coal dust samples an exposure of 11 C/kg is generally used. The efficiency of the method can be seen from fig. 2 where cytotoxicity results of a biological in-vitro cell test are compared with a TL-estimation of toxicity for 50 dust samples. These originated from different sands and stones used in foundries, which have been investigated with respect to their silicosis risk by a cooperative research project between several institutions. Presently the TL-method is used in tests for coal mine dust in a modified manner. Since coal can hardly be wetted by water methanol is used. The first preliminary results from 25 samples of air-borne dust agreed fairly well with epidemiological data. It turned out that even at a
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7
8
9
10 11 12 13
14
SAMPLES
Fig. 2. C y t o t o x i c i t y (a) and TL-estimation o f t o x i c i t y (b) o f
50 respirabte dust samples: (a) determined by K. Robock at the Institut f. Hygiene und Arbeitsmedizin, Gesamthochschule Essen by measuring the TTC-reduction activity of peritoneal macrophages of guinea pigs after dust incubation for 2 h (for details of the test see [9]). 100% means inert behaviour. The toxicity increases with declining ordinate values. (b) wt = weak toxicity or inert, mt = medium toxicity, ht = high toxicity, vht = very high toxicity.
quartz content of only 0.09% the typical TL-curve of quartz can be obtained.
References [1 ] M.T.R. Reisner, Gliickauf 113 (1977) 21. [2] W. Kriegseis, A. Scharmann and J. Serafin, Ergebn. v. Untersuchungen a.d.G.d. Staub- u. Silikosebek'~mpfung im Steinkohlenbergbau 12 (1979) 149. [3] W. Kriegseis, A. Scharmann and A. Joshi, ibid. 12 (1979) 159. [4] W. Kriegseis, A. Scharmann and J. Serafin, ibid. 11 (1977) 125. [5] W.L. Medlin, J. Chem. Phys. 38 (1963) 1132. [6] M. Schlesinger, J. Phys. Chem. Solids 26 (1965) 1761. [7] A. Halperin, A.A. Braner and J. Shapira, J. Luminescence 1 (1970) 385. [8] P.L. Mattern, K. Lengweiler and P.W. Levy, Rad. Eft. 26 (1975) 237. [9] K. Robock, Beitr. Silikose-Forsch. 26 (1974) 111.