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Characterization of haul road dust in an Indian opencast iron ore mine
Pergamon PII:
Atmospheric Environment Vol. 31, No. 17, pp. 2809-2814, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain S1352-2310(97)00095--2 1352-2310/97 $17.00 + 0.00
CHARACTERIZATION OF HAUL ROAD DUST IN AN INDIAN OPENCAST IRON ORE MINE S U B R A T O S I N H A a n d S. P. B A N E R J E E * Tara Energy Research Institute, Habitat Place, Lodi Road, New Delhi 110003, India; and *Indian Institute of Coal Management, Kanke Road, Ranchi 834006, Bihar, India (First received 15 July 1995 and in final form 24 January 1997. Published June 1997)
Abstract--Vehicular traffic on unpaved haul roads of the opencast mines has been identified as the most prolificsource of fugitivedust. An intensive study was carried out in Noamundi Iron ore mines of Tata Iron and Steel Co. in January-February 1994 to characterize the airborne aerosol mainly contributed from unpaved haul road, trafficexhaust and re-entrained dust from the other activitiesof the mine. Percentage of suspended particulate matter at the various size ranges and free silica content of each of the size ranges of haul road dust were determined. Concentrations of eight trace elements, namely, zinc, copper, lead, manganese, cobalt, nickel, cadmium and iron were determined and found to be varying in the range 13.92-16.34, 0.06-0.09, 0.71-0.79, 0.14-0.15, 0.08-0.11, 0.15-0.17, 0.003-0.004 and 390-401.20#gm -3, respectively. A study on enrichment factor and varimax rotated factor analysis indicates the four major sources namely soil/road dust, vehicle exhaust, metallic corrosion and, galvanized material, tire wear and zinc compound in rubber material which appear to contribute trace elements to airborne aerosol. © 1997 Elsevier Science Ltd. Key word index: Haul road, fugitivedust, emission factor, trace element, enrichment factor, SPM, PM-10, factor analy,,;is.
l. INTRODUCTION The airborne dust from machines working on overburden and iron ore benches, crushing and screening plants, transport equipment and especially the unpaved haul roads are posing major problems in the working of opencast mines. The vehicular traffic on an unpaved haul road has been identified as the most important cause of fugitive dust emission. The uncontrolled airborne dust not only creates serious health hazard but also affects the productivity through poor visibility, and increased maintenance cost. In addition, the fugitive dust travels over long distances, causing deterioration of ambient air quality in and around the mining site. The size, silica and trace element content of the airborne dust are important parameters governing the dispersion as well as health effect of the dust. Tile results of study on characterization of the airborne aerosol which is mainly contributed from unpaw,~d haul road, vehicular traffic exhaust and re-entrained dust from the other activities in Noamundi iron-ore mine, are reported in this paper. The physical characteristics of airborne mine dust most often associated with the incidence of health hazard are the size distribution and mass concentration of the dust. Medical researchers concluded that it is mostly the minu,; 5-pm fraction of the pulmonary
dust which is harmful t o human health and, in particular, the minus 3-#m particles which tend to accumulate in the lungs (Cartwright, 1967; Kotrappa,1972; Thakur, 1974). In India, Regulation 124 of the Metalliferous Mine Regulations, 1961 was comprehensively amended in 1988 to strengthen the provisions relating to precautions against pneumoconiosis. A place is not deemed fit for work if the airborne respirable dust concentration exceeds 3 mgm -a provided the free silica present in the dust is less than 5%. The study conducted by Sastry et al. (1994) in two mechanized opencast iron ore mines revealed that the free silica content adjacent to the haul roads were 1.28 + 0.12% and 0.68 + 0.13%, respectively. The origin of trace elements in iron ore can be related to the very initial stage of its formation. It has been reported that certain metallic particulate such as cadmium, chromium, mercury, lead, etc. in ambient air in excessive concentrations caused toxic effects on plants animals and humans. They are the most insidious pollutants because of their non-biodegradable nature and property to affect all forms of the ecological system. Sometimes the cumulative effect of two or more pollutants in air have been reported to be more serious than the effect due to individual pollutants (Ohta and Okita, 1990). Many studies so far have been done in India and abroad on the trace element concentration of urban aerosols and attempts were
2809
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S. SINHA and S. P. BANERJEE
made to identify the source of trace elements through factor analysis (Negi et al., 1987; Sadasivan et al., 1990; Fergusson and Kim, 1991) but very little work has been carried out on the elemental compositions of aerosol in the mining areas. An intensive study was made in the Noamundi Iron Ore mines (NIOM), a hilly iron ore deposit, of Tata Iron and Steel Co. (Dist.: West Singhbhum, Bihar) for a period of one month in 1994 to characterize the airborne haul road dust. The percentage of suspended particulate matter (SPM) at the various size ranges and free silica content of each of the size ranges are given in this paper. The mean concentration of eight trace elements in SPM obtained at the various stations of the mine have also been incorporated. The enrichment factors (EF) for eight trace elements have been provided. Varimax Rotated Factor analysis has been utilized to get an idea about the association of the trace elements to various possible natural and anthropogenic sources.
2. M E T H O D O L O G Y
2.1. Sampling stations In this study, three sampling stations situated in the downwind side of the haul road of Noamundi Iron ore mines were selected by using the criteria of (i)
traffic density, (ii) obstruction of upwind/downwind air flow, and (iii) availability of electric power for operation of the sampling equipment. Figure 1 shows the surface plan and location of three sampling stations of NIOM. 2.2. Sampling frequency The study was conducted for a period of one month from 15 January 1994 to 15 February 1994 to observe the physical, chemical and mineralogical characteristics of the dust emanating from the haul road of NIOM. Daily sampling (24 h) was done over the period of one month to measure the SPM around the haul road. 2.3. Sampling procedure Three Hi-Volume Samplers (HVS) of model Envirotech APM 410 were employed at three sampling stations during the one month of study. Whatman-make EPM 2000 filter paper (size 20.3 x 25.4 cm) was used as the collection media of SPM, and the flowrates of the samplers were kept within 1.1-1.5 m3min -1 during the entire sampling period. The filter papers were conditioned in the desiccator for at least 24 h before weighing. The two five-stage cascade impactors (model SA 235 of Sierra Anderson make) (five stages of 0.05-1.1 #m, 1.1-2.0 #m, 2.0-3.3 #m, 3.3-7.0 pm and greater than 7.0 pm, adapted to standard HVS, were positioned to
-St.3 t , EXPlERIMENT&t
1 PLOTS
~
" 600 RL
WAY TO UPPEP gENCN~$
Fig. 1. Haul roads of Noamundi iron ore mine, TISCO.
.[Scale
1:71/-.0
Characterization of haul road dust measure the size distribution and respirable mass fraction of airborne particulate. A wind monitor, a temperature recorder and a hygrometer were kept at a fixed station in the mine during the entire sampling period. 2.4. Size frequency distribution of SPM Particle size distribution of SPM emanating from the haul road of N I O M was analyzed by using a Malvern Instruments Master Particle Sizer (Model M 3.1) available at the Indian Bureau of Mines, Nagpur. The airborne SPM were collected by using the aluminum-foil collection media in the five-stage cascade impactor. 2.5. Free silica coment The SPM as collected in the Cascade Impactor in five different size ranges of 0.05-1.1 pm, 1.1-2.0/tin, 2.0-3.3 #m, 3.3-7.0 #m and > 7.0/zm were analyzed by the orthophosphoric acid method (after Talvitie, 195l) to obtain the free silica content at those size ranges. 2.6. Trace elements in SPM The concentration of eight trace elements in SPM were determined by atomic absorption spectrophotometer (AAS) (Model: GBC 902, Sensitivity: concentration of an element that will produce a transmittance of 99% (absorbance of 0.0044), Detection limit: minimum concentration can be detected with 95% certainty, Oplimum working range: concentration range of an element that will produce an absorbance range of 0.2-0.8 abs.) after digesting the EPM 2000 filter paper in 15 ml of concentrated nitric acid. Nitric acid extraction of SPM samples is the most suitable extraction system for the determination of trace elements by AAS (Janssens and Dums, 1973, 1974; Tinsley et al., 1983). The concentration of individual elements in the solution was determined by comparing the absorbance of the standard metal solution. Samples were directly introduced into the frame of continuous aspiration through polyethylene tubing and the concentration~of the object element (#g m l - 1) was obtained from the calibration plot. The concentration of an element in the atmosphere is obtained from the following :relation:
A(/~g m - 3) _
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An EF could be obtained by the formula: EF = (X/Fe)~i~ (X/Fe).~t where (X/Fe)alr refers to the ratio of the concentration of an element (X) to that of(iron) in air, divided by the corresponding abundance ratio in crustal rocks (Mason, 1966). The earth's crust contains 5% iron, and more so, as the study was conducted in an iron ore mine, this element of highest concentration was chosen as the reference element. 2.8. Factor analysis In order to interpret the significance of atmospheric levels of air pollutants, it is necessary to acquire some knowledge of their sources. Although there are many statistical techniques to extract information on the type of air pollution sources, factor analysis is a commonly used method for this purpose (Stevens and Pace, 1984). Factor analysis, a useful explanatory tool in multivariate statistical analysis can be applied to discover and interpret relationships among variables and to test different hypotheses. The correlation coefficient matrix, factor loading and scores obtained from factor analysis are utilized to draw inferences about artificial and natural occurrence of the various trace elements (Hopke et al., 1976; Sadasivan and Negi, 1990; Sharma, 1991; Fergusson and Kim, 1991).
3. RESULTS AND DISCUSSION
The average particle size distribution of SPM and PM-10 emanating from the haul road of N I O M is presented in Figs 2 and 3. The PM-10 at 0.05-1.1/~m,l.l-2.0/tm, 2.0-3.3 #m, 3.3-7.0#m and > 7.0/~m size ranges were found to be 5%, 8%, 15%, 28% and 44%, respectively, and about 60% of the total SPM (size range 0.05-100 #m) was observed to be within the 0-10/~m size range (PM-10). The values of size range and respective cumulative percentage of SPM were further plotted in an arithmetic probability chart and it was observed that the size frequency was not normally distributed.
Amount of element (#g.ml).Total volume of sample (ml) Vol. of sampled air (m3) • Percent of collection area used sampled'
2.7. Enrichment factor ( EF) EF provides an idea regarding the association of trace elements to the earth's crust and anthropogenic sources. Dust particles are an obvious source for trace elements in the mining areas. A further attempt was made to ascribe the extent of soil borne elements derived from air to those elements in the earth's crust.
The free silica content at five different size ranges of airborne haul road dust was determined and was found to be 1.15%, 1.30%, 1.30%, 1.20% and 1.10% for the 0.05-1.1#m, 1.1-2.0#m, 2.0-3.3pm, 3.3-7.0 #m and greater than 7.0/~m size ranges, respectively. The free silica content was found to be slightly higher in the finer size ranges of SPM.
2812
S. SINHA and S. P. BANERJEE 100
u
I
!
9
I
I
i
I
I
f
~
50
n
.
.
.
.
.
.
[
10
J
,
I
I
I
•
•
'|
!
|
|
|
''
'
1000
100 Particle Size (IJrn)
Fig. 2. Percentage size frequency distribution of haul road dust in Noamundi iron ore mine.
>7urn 44%
0.0,5-1.1 um 5% .1-2 um 8%
3.3-7 um 28% 2-3.3 urn 1,.5'~
Fig. 3. Size frequency distribution of haul road dust in Noamundi iron ore mine.
The concentration of eight trace elements in S P M were determined by AAS (Model G B C 902). The concentration of zinc (Zn), copper (Cu), lead (Pb), manganese (Mn), cobalt (Co), nickel (Ni), cadmium (Cd) and iron (Fe) in SPM at three sampling stations was found to be varying in the range 13.92-16.34,
0.06-0.09, 0.71-0.79, 0.14-0.15, 0.08-0.11, 0.15-0.17, 0.003-0.004 and 390-401.20#gm -a as shown in Table 1. The m a x i m u m and m i n i m u m levels, arithmetic and geometric mean concentration with standard deviation (SD) are also given in Table 1. The Pb content was found to be lower than the prescribed ambient air quality standard (India) of 1.5 Fg m - 3 for industrial area but was marginally higher than the prescribed ambient air quality standard (AAQ) of U S E P A (0.7 Fgm-3). Concentration of all trace elements (including Pb) were found to be less than the prescribed threshold level values of U S E P A (1, 0.15, 5.0, 0.05, 5 and 1.0 mg m - 3 for Cu, Pb, Zn, Mn, Fe and Ni, respectively) (Sax et al., 1986). The logarithmic values of E F for eight trace elements have been given in Fig. 4. An EF less than or equal to unity for Fe, Mn, and Cd indicated the association of sources of these elements to the earth's crust. The E F value for Ni was found to be a little higher than unity, whereas Co, Z n and Pb were found to be highly enriched in&*cating that these might have been contributed by anthropogenic sources. The very high E F for Pb indicates vehicular exhausts as major sources of pollution.
Table 1. Mean elemental composition (#g m - 3) of SPM near haul road of Noamundi iron ore mine Element Zn Cu Pb Mn Co Ni Cd Fe
Minimum 13.92 0.06 0.71 0.14 0.09 0.16 0.003 390.0
Maximum 16.34 0.09 0.79 0.15 0.11 0.17 0.004 401.2
Arithmetic mean 4- s.d 15.13 4- 1.21 0.08 + 0.01 0.75 4- 0.04 0.15 -I- 0.005 0.09 4- 0.01 : 0.16 4- 0.007 0.003 + 0.001 395.60 _ 5.59
Geometric mean 4- s.d 15.08 -I- 1.12 0.07 + 67.75 0.75 4- 195.04 0.15 _ 197.20 0.09 -I- 325.11 0.16 + 645.07 0.003 -I- 935.04 395.60 4- 46.48
No. of samples 15 15 15 15 15 15 15 15
Characterization of haul road dust
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log EF ( H R D / S O I L ) 2.5 2 1.5 I o.8
o -o.5
Cd
Mn
Fe
NI Cu ELEMENT
Co
Zn
Pb
Fig. 4. Enrichment factor of different elements in haul road dust(HRD) of Noamundi iron ore mine.
Table 2. Correlation coefficient matrix for aerosols of Noamundi iron ore mine Variables SPM Zn Cu Pb Mn Co Ni Cd Fe
SPM
Zn
Cu
Pb
Mn
1.00
0.43 1.00
- 0.97 - 0.21 1.00
- 0.74 0.93 - 0.57 1.00
0.55 0.96 0.08 0.78 1.00
Co -
0.15 0.96 0.08 0.78 1.00 1.00
Ni
Cd
Fe
0.69 0.95 - 0.50 0.98 0.82 - 0.82 1.00
0.78 - 0.23 - 0.90 0.16 - 0.50 0.50 0.08 1.00
0.99 0.53 - 0.94 0.82 0.57 - 0.27 0.77 0.69 1.00
Table 3 Varimax rotated factor loading matrix for aerosols of Noamundi iron ore mine Variables
Factor 1
SPM Zn Cu Pb Mn Co Ni Cd Fe Eigen value P,~rcent of trace Cumulative percent of trace
-
Factor 2
0.2744 0.9863 0.9989 0.8492 0.1230 0.9924 0.8858 0.3896 0.3864
0.9616 0.1650 - 0.0465 0.5281 0.9924 0.1230 0.4640 0.9210 0.9223
5.6340 62.60 62.60
3.3659 37.40 100.00
Communality 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
Number of rotations: 38.
The correlation coefficient matrix for aerosols of N o a m u n d i iron ore mines are given in Table 2. A very high correlation coefficient was observed between S P M , and Fe, M n and Cd. A n o t h e r g o o d correlation of Z n and Ni was found with Pb. Two factors were o b t a i n e d from the varimax rotated factor loading matrix for aerosols of N I O M and are presented in Table 3. The two factors together account for 100% of the variance. In the first factor, which was 62.60% of the total variance, a high load-
ing from Pb, Zn, Cu, Ni and Co were observed. M a n y researchers have associated the origin of these elements particularly, Pb, with vehicular exhaust and Cu and Ni from corrosion of metallic parts (Fergusson and Kim, 1991). G a a r e n t r o o m et al. (1977) and H o p k e et al. (1980) associated a similar factor with high loading of P b to vehicular emission. F r o m their study on road dust, Fergusson and K i m (1991) concluded that the Z n could be contributed from galvanised materials, tire wear and the use of
2814
S. SINHA and S. P. BANERJEE
zinc c o m p o u n d in rubber production. Another high loading for SPM, Mn, Cd and Fe were obtained in the second factor which was 37.40% of the total variance. A high correlation coefficient was found between these elements. High factor loading and good correlation coefficient of these elements indicated the association of Mn, Cd and Fe with soil/iron ore sources.
4. CONCLUSIONS The following conclusions are made on the basis of the investigation conducted in N I O M : 1. The particle size distribution of airborne dust emanating from the haul road of N I O M was found to be log-normally distributed. About 60% of the total S P M was found to be within the 0-10/~m size range (PM-10). 2. The free silica content for five different size ranges of airborne haul road dust was found to be varying from 1.1 to 1.3%. The free silica content was found to be slightly higher in the finer size fraction of the particulate matter. 3. The concentration of Pb was observed to be marginally higher than the prescribed ambient air quality standard of U S E P A , but concentrations for all trace elements were found to be less than the prescribed threshold level values of U S E P A . The concentration of Pb was found to be lower than the National ambient air quality standard (India) of 1.5 # g m -3 for industrial area. 4. An E F value less than or equal to unity for Fe, Cd and M n indicated the sources as the earth's crust. An E F value slightly higher than unity was observed for Ni and Cu, whereas Co, Zn and Pb have been found highly enriched and these might have been contributed by anthropogenic sources. 5. The study of factor analysis to determine the sources of trace elements have indicated four major sources which appear to contribute trace elements to total particulate load. These are wind borne soil/road dust (SPM, Mn, Cd, Fe), vehicle exhaust (Pb), metallic corrosion (Cu, Ni), galvanized material, tire wear and zinc c o m p o u n d in rubber material (Zn). Acknowledgements--Financial support for carrying out this study from the Ministry of Environment and Forests, Govt. of India and Tata Iron and Steel Co., OMQ Division, is gratefully acknowledged. The authors are thankful to the authorities of Noamundi Iron ore mines, TISCO for permission to collect information and make measurements in their mines.
REFERENCES Cartwright, J. (1967) Airborne dust in coal mines: the particle-size-selection characteristics of lung and the diserable characteristics of dust-sampling instruments. In Inhaled Particles and Vapours II (edited by Davies C.), pp. 393-406. Pergamon Press, London. Fergusson, J. E. and Kim, N. D. (1991) Trace elements in street and house dusts: sources and speciation. The Science of the Total Environment 100, 125-150. Gaarenstroom, P. D., Perone, S. P. and Moyers, J. L. (1977) Application of pattern recognition and factor analysis for characterisation of atmospheric particulate composition in southwest desert atmosphere. Environment Science and Technology 11,795-800. Hopke, P. K., Gladney, E. S., Gordon, G. E., Zoller, W. H. and Jones, A. G. (1976) The use of multivariate analysis to identify sources of selected elements in the Boston urban aerosols. Atmospheric Environment 10, 1015-1025. Hopke, P. K., Lamb, R. E. and Natuach, E. S. (1980) Multielemental characterisation of urban roadway dust. Environment Science and Technology 14, 164-172. Janssens, M. and Dams, R. (1973) Analitica Chemica Acta, 65, 41. Janssens, M. and Dams, R. (1974) Analitica Chemica Acta 70, 25. Kotrappa, P. (1972) Shape factors for aerosols of coal, UO2 and TiO2 in respirable size range, assessment of airborne particles. Proceedings of the 3rd Rochester International Conference on Environmental Toxicity, Rochester, New York. Mason, B. (1966) Principles of Geology, 3rd Edn. Wiley, New York. Negi, B. S., Sadasivan, S. and Mishra, U. C. (1987) Aerosol composition and sources in urban areas in India. Atmospheric Environment 21, 1259-1266. Ohta, S. and Okita, T. (1990) A chemical characterisation of atmospheric aerosols in Sappro. Atmospheric Environment 24, 815-822. Sadasivan, S. and Negi, B. S. (1990) Elemental characterisation of atmospheric aerosols. The Science of the Total Environment 96, 269-279. Sastry, B. S., Roy, S. C. and Mishra, G. B. (1994) Respirable dust concentration--A case study for a group of mines and crushing plants. In Proceedings of the International Symposium on the Impacts of Mining on the Environmental Problems and Solutions (edited by Paithankar A. G.). VRCE, Nagpur, India. Sax, N. O., Richard, J. and Lewis, S. R. (1986) Hazardous Chemicals in the Working Place. Van Nostrand Reinhold, New York. Sharma, P. K. (1991) Investigation on air quality assessment in some coal mining areas of Raniganj coalfield of India. Ph.D. thesis, ISM, Dhanbad, India. Stevens, R. K. and Pace, T. G. (1984) Overview of the mathematical and emperical receptor models workshop (Quil Roost II). Atmospheric Environment 18, 1497-1500. Talvitie, N. A. (1951) Analytical Chemistry 23, 623. Thakur, P. C. (1974) Mass distribution of respirable dust particles from U.S. coals. Colliery Guardian 222, 236-239. Ministry of Labour, Government of India (1961) The Metalliferous Mines Regulations. Tinsley, D. A., Baron, A. R., Critchley, R. and Williamson, R. J. (1983) International Journal of Environmental Analytical Chemistry 14, 285.
Atmospheric Environment Vol. 31, No. 17, pp. 2809-2814, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain S1352-2310(97)00095--2 1352-2310/97 $17.00 + 0.00
CHARACTERIZATION OF HAUL ROAD DUST IN AN INDIAN OPENCAST IRON ORE MINE S U B R A T O S I N H A a n d S. P. B A N E R J E E * Tara Energy Research Institute, Habitat Place, Lodi Road, New Delhi 110003, India; and *Indian Institute of Coal Management, Kanke Road, Ranchi 834006, Bihar, India (First received 15 July 1995 and in final form 24 January 1997. Published June 1997)
Abstract--Vehicular traffic on unpaved haul roads of the opencast mines has been identified as the most prolificsource of fugitivedust. An intensive study was carried out in Noamundi Iron ore mines of Tata Iron and Steel Co. in January-February 1994 to characterize the airborne aerosol mainly contributed from unpaved haul road, trafficexhaust and re-entrained dust from the other activitiesof the mine. Percentage of suspended particulate matter at the various size ranges and free silica content of each of the size ranges of haul road dust were determined. Concentrations of eight trace elements, namely, zinc, copper, lead, manganese, cobalt, nickel, cadmium and iron were determined and found to be varying in the range 13.92-16.34, 0.06-0.09, 0.71-0.79, 0.14-0.15, 0.08-0.11, 0.15-0.17, 0.003-0.004 and 390-401.20#gm -3, respectively. A study on enrichment factor and varimax rotated factor analysis indicates the four major sources namely soil/road dust, vehicle exhaust, metallic corrosion and, galvanized material, tire wear and zinc compound in rubber material which appear to contribute trace elements to airborne aerosol. © 1997 Elsevier Science Ltd. Key word index: Haul road, fugitivedust, emission factor, trace element, enrichment factor, SPM, PM-10, factor analy,,;is.
l. INTRODUCTION The airborne dust from machines working on overburden and iron ore benches, crushing and screening plants, transport equipment and especially the unpaved haul roads are posing major problems in the working of opencast mines. The vehicular traffic on an unpaved haul road has been identified as the most important cause of fugitive dust emission. The uncontrolled airborne dust not only creates serious health hazard but also affects the productivity through poor visibility, and increased maintenance cost. In addition, the fugitive dust travels over long distances, causing deterioration of ambient air quality in and around the mining site. The size, silica and trace element content of the airborne dust are important parameters governing the dispersion as well as health effect of the dust. Tile results of study on characterization of the airborne aerosol which is mainly contributed from unpaw,~d haul road, vehicular traffic exhaust and re-entrained dust from the other activities in Noamundi iron-ore mine, are reported in this paper. The physical characteristics of airborne mine dust most often associated with the incidence of health hazard are the size distribution and mass concentration of the dust. Medical researchers concluded that it is mostly the minu,; 5-pm fraction of the pulmonary
dust which is harmful t o human health and, in particular, the minus 3-#m particles which tend to accumulate in the lungs (Cartwright, 1967; Kotrappa,1972; Thakur, 1974). In India, Regulation 124 of the Metalliferous Mine Regulations, 1961 was comprehensively amended in 1988 to strengthen the provisions relating to precautions against pneumoconiosis. A place is not deemed fit for work if the airborne respirable dust concentration exceeds 3 mgm -a provided the free silica present in the dust is less than 5%. The study conducted by Sastry et al. (1994) in two mechanized opencast iron ore mines revealed that the free silica content adjacent to the haul roads were 1.28 + 0.12% and 0.68 + 0.13%, respectively. The origin of trace elements in iron ore can be related to the very initial stage of its formation. It has been reported that certain metallic particulate such as cadmium, chromium, mercury, lead, etc. in ambient air in excessive concentrations caused toxic effects on plants animals and humans. They are the most insidious pollutants because of their non-biodegradable nature and property to affect all forms of the ecological system. Sometimes the cumulative effect of two or more pollutants in air have been reported to be more serious than the effect due to individual pollutants (Ohta and Okita, 1990). Many studies so far have been done in India and abroad on the trace element concentration of urban aerosols and attempts were
2809
2810
S. SINHA and S. P. BANERJEE
made to identify the source of trace elements through factor analysis (Negi et al., 1987; Sadasivan et al., 1990; Fergusson and Kim, 1991) but very little work has been carried out on the elemental compositions of aerosol in the mining areas. An intensive study was made in the Noamundi Iron Ore mines (NIOM), a hilly iron ore deposit, of Tata Iron and Steel Co. (Dist.: West Singhbhum, Bihar) for a period of one month in 1994 to characterize the airborne haul road dust. The percentage of suspended particulate matter (SPM) at the various size ranges and free silica content of each of the size ranges are given in this paper. The mean concentration of eight trace elements in SPM obtained at the various stations of the mine have also been incorporated. The enrichment factors (EF) for eight trace elements have been provided. Varimax Rotated Factor analysis has been utilized to get an idea about the association of the trace elements to various possible natural and anthropogenic sources.
2. M E T H O D O L O G Y
2.1. Sampling stations In this study, three sampling stations situated in the downwind side of the haul road of Noamundi Iron ore mines were selected by using the criteria of (i)
traffic density, (ii) obstruction of upwind/downwind air flow, and (iii) availability of electric power for operation of the sampling equipment. Figure 1 shows the surface plan and location of three sampling stations of NIOM. 2.2. Sampling frequency The study was conducted for a period of one month from 15 January 1994 to 15 February 1994 to observe the physical, chemical and mineralogical characteristics of the dust emanating from the haul road of NIOM. Daily sampling (24 h) was done over the period of one month to measure the SPM around the haul road. 2.3. Sampling procedure Three Hi-Volume Samplers (HVS) of model Envirotech APM 410 were employed at three sampling stations during the one month of study. Whatman-make EPM 2000 filter paper (size 20.3 x 25.4 cm) was used as the collection media of SPM, and the flowrates of the samplers were kept within 1.1-1.5 m3min -1 during the entire sampling period. The filter papers were conditioned in the desiccator for at least 24 h before weighing. The two five-stage cascade impactors (model SA 235 of Sierra Anderson make) (five stages of 0.05-1.1 #m, 1.1-2.0 #m, 2.0-3.3 #m, 3.3-7.0 pm and greater than 7.0 pm, adapted to standard HVS, were positioned to
-St.3 t , EXPlERIMENT&t
1 PLOTS
~
" 600 RL
WAY TO UPPEP gENCN~$
Fig. 1. Haul roads of Noamundi iron ore mine, TISCO.
.[Scale
1:71/-.0
Characterization of haul road dust measure the size distribution and respirable mass fraction of airborne particulate. A wind monitor, a temperature recorder and a hygrometer were kept at a fixed station in the mine during the entire sampling period. 2.4. Size frequency distribution of SPM Particle size distribution of SPM emanating from the haul road of N I O M was analyzed by using a Malvern Instruments Master Particle Sizer (Model M 3.1) available at the Indian Bureau of Mines, Nagpur. The airborne SPM were collected by using the aluminum-foil collection media in the five-stage cascade impactor. 2.5. Free silica coment The SPM as collected in the Cascade Impactor in five different size ranges of 0.05-1.1 pm, 1.1-2.0/tin, 2.0-3.3 #m, 3.3-7.0 #m and > 7.0/zm were analyzed by the orthophosphoric acid method (after Talvitie, 195l) to obtain the free silica content at those size ranges. 2.6. Trace elements in SPM The concentration of eight trace elements in SPM were determined by atomic absorption spectrophotometer (AAS) (Model: GBC 902, Sensitivity: concentration of an element that will produce a transmittance of 99% (absorbance of 0.0044), Detection limit: minimum concentration can be detected with 95% certainty, Oplimum working range: concentration range of an element that will produce an absorbance range of 0.2-0.8 abs.) after digesting the EPM 2000 filter paper in 15 ml of concentrated nitric acid. Nitric acid extraction of SPM samples is the most suitable extraction system for the determination of trace elements by AAS (Janssens and Dums, 1973, 1974; Tinsley et al., 1983). The concentration of individual elements in the solution was determined by comparing the absorbance of the standard metal solution. Samples were directly introduced into the frame of continuous aspiration through polyethylene tubing and the concentration~of the object element (#g m l - 1) was obtained from the calibration plot. The concentration of an element in the atmosphere is obtained from the following :relation:
A(/~g m - 3) _
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An EF could be obtained by the formula: EF = (X/Fe)~i~ (X/Fe).~t where (X/Fe)alr refers to the ratio of the concentration of an element (X) to that of(iron) in air, divided by the corresponding abundance ratio in crustal rocks (Mason, 1966). The earth's crust contains 5% iron, and more so, as the study was conducted in an iron ore mine, this element of highest concentration was chosen as the reference element. 2.8. Factor analysis In order to interpret the significance of atmospheric levels of air pollutants, it is necessary to acquire some knowledge of their sources. Although there are many statistical techniques to extract information on the type of air pollution sources, factor analysis is a commonly used method for this purpose (Stevens and Pace, 1984). Factor analysis, a useful explanatory tool in multivariate statistical analysis can be applied to discover and interpret relationships among variables and to test different hypotheses. The correlation coefficient matrix, factor loading and scores obtained from factor analysis are utilized to draw inferences about artificial and natural occurrence of the various trace elements (Hopke et al., 1976; Sadasivan and Negi, 1990; Sharma, 1991; Fergusson and Kim, 1991).
3. RESULTS AND DISCUSSION
The average particle size distribution of SPM and PM-10 emanating from the haul road of N I O M is presented in Figs 2 and 3. The PM-10 at 0.05-1.1/~m,l.l-2.0/tm, 2.0-3.3 #m, 3.3-7.0#m and > 7.0/~m size ranges were found to be 5%, 8%, 15%, 28% and 44%, respectively, and about 60% of the total SPM (size range 0.05-100 #m) was observed to be within the 0-10/~m size range (PM-10). The values of size range and respective cumulative percentage of SPM were further plotted in an arithmetic probability chart and it was observed that the size frequency was not normally distributed.
Amount of element (#g.ml).Total volume of sample (ml) Vol. of sampled air (m3) • Percent of collection area used sampled'
2.7. Enrichment factor ( EF) EF provides an idea regarding the association of trace elements to the earth's crust and anthropogenic sources. Dust particles are an obvious source for trace elements in the mining areas. A further attempt was made to ascribe the extent of soil borne elements derived from air to those elements in the earth's crust.
The free silica content at five different size ranges of airborne haul road dust was determined and was found to be 1.15%, 1.30%, 1.30%, 1.20% and 1.10% for the 0.05-1.1#m, 1.1-2.0#m, 2.0-3.3pm, 3.3-7.0 #m and greater than 7.0/~m size ranges, respectively. The free silica content was found to be slightly higher in the finer size ranges of SPM.
2812
S. SINHA and S. P. BANERJEE 100
u
I
!
9
I
I
i
I
I
f
~
50
n
.
.
.
.
.
.
[
10
J
,
I
I
I
•
•
'|
!
|
|
|
''
'
1000
100 Particle Size (IJrn)
Fig. 2. Percentage size frequency distribution of haul road dust in Noamundi iron ore mine.
>7urn 44%
0.0,5-1.1 um 5% .1-2 um 8%
3.3-7 um 28% 2-3.3 urn 1,.5'~
Fig. 3. Size frequency distribution of haul road dust in Noamundi iron ore mine.
The concentration of eight trace elements in S P M were determined by AAS (Model G B C 902). The concentration of zinc (Zn), copper (Cu), lead (Pb), manganese (Mn), cobalt (Co), nickel (Ni), cadmium (Cd) and iron (Fe) in SPM at three sampling stations was found to be varying in the range 13.92-16.34,
0.06-0.09, 0.71-0.79, 0.14-0.15, 0.08-0.11, 0.15-0.17, 0.003-0.004 and 390-401.20#gm -a as shown in Table 1. The m a x i m u m and m i n i m u m levels, arithmetic and geometric mean concentration with standard deviation (SD) are also given in Table 1. The Pb content was found to be lower than the prescribed ambient air quality standard (India) of 1.5 Fg m - 3 for industrial area but was marginally higher than the prescribed ambient air quality standard (AAQ) of U S E P A (0.7 Fgm-3). Concentration of all trace elements (including Pb) were found to be less than the prescribed threshold level values of U S E P A (1, 0.15, 5.0, 0.05, 5 and 1.0 mg m - 3 for Cu, Pb, Zn, Mn, Fe and Ni, respectively) (Sax et al., 1986). The logarithmic values of E F for eight trace elements have been given in Fig. 4. An EF less than or equal to unity for Fe, Mn, and Cd indicated the association of sources of these elements to the earth's crust. The E F value for Ni was found to be a little higher than unity, whereas Co, Z n and Pb were found to be highly enriched in&*cating that these might have been contributed by anthropogenic sources. The very high E F for Pb indicates vehicular exhausts as major sources of pollution.
Table 1. Mean elemental composition (#g m - 3) of SPM near haul road of Noamundi iron ore mine Element Zn Cu Pb Mn Co Ni Cd Fe
Minimum 13.92 0.06 0.71 0.14 0.09 0.16 0.003 390.0
Maximum 16.34 0.09 0.79 0.15 0.11 0.17 0.004 401.2
Arithmetic mean 4- s.d 15.13 4- 1.21 0.08 + 0.01 0.75 4- 0.04 0.15 -I- 0.005 0.09 4- 0.01 : 0.16 4- 0.007 0.003 + 0.001 395.60 _ 5.59
Geometric mean 4- s.d 15.08 -I- 1.12 0.07 + 67.75 0.75 4- 195.04 0.15 _ 197.20 0.09 -I- 325.11 0.16 + 645.07 0.003 -I- 935.04 395.60 4- 46.48
No. of samples 15 15 15 15 15 15 15 15
Characterization of haul road dust
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log EF ( H R D / S O I L ) 2.5 2 1.5 I o.8
o -o.5
Cd
Mn
Fe
NI Cu ELEMENT
Co
Zn
Pb
Fig. 4. Enrichment factor of different elements in haul road dust(HRD) of Noamundi iron ore mine.
Table 2. Correlation coefficient matrix for aerosols of Noamundi iron ore mine Variables SPM Zn Cu Pb Mn Co Ni Cd Fe
SPM
Zn
Cu
Pb
Mn
1.00
0.43 1.00
- 0.97 - 0.21 1.00
- 0.74 0.93 - 0.57 1.00
0.55 0.96 0.08 0.78 1.00
Co -
0.15 0.96 0.08 0.78 1.00 1.00
Ni
Cd
Fe
0.69 0.95 - 0.50 0.98 0.82 - 0.82 1.00
0.78 - 0.23 - 0.90 0.16 - 0.50 0.50 0.08 1.00
0.99 0.53 - 0.94 0.82 0.57 - 0.27 0.77 0.69 1.00
Table 3 Varimax rotated factor loading matrix for aerosols of Noamundi iron ore mine Variables
Factor 1
SPM Zn Cu Pb Mn Co Ni Cd Fe Eigen value P,~rcent of trace Cumulative percent of trace
-
Factor 2
0.2744 0.9863 0.9989 0.8492 0.1230 0.9924 0.8858 0.3896 0.3864
0.9616 0.1650 - 0.0465 0.5281 0.9924 0.1230 0.4640 0.9210 0.9223
5.6340 62.60 62.60
3.3659 37.40 100.00
Communality 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
Number of rotations: 38.
The correlation coefficient matrix for aerosols of N o a m u n d i iron ore mines are given in Table 2. A very high correlation coefficient was observed between S P M , and Fe, M n and Cd. A n o t h e r g o o d correlation of Z n and Ni was found with Pb. Two factors were o b t a i n e d from the varimax rotated factor loading matrix for aerosols of N I O M and are presented in Table 3. The two factors together account for 100% of the variance. In the first factor, which was 62.60% of the total variance, a high load-
ing from Pb, Zn, Cu, Ni and Co were observed. M a n y researchers have associated the origin of these elements particularly, Pb, with vehicular exhaust and Cu and Ni from corrosion of metallic parts (Fergusson and Kim, 1991). G a a r e n t r o o m et al. (1977) and H o p k e et al. (1980) associated a similar factor with high loading of P b to vehicular emission. F r o m their study on road dust, Fergusson and K i m (1991) concluded that the Z n could be contributed from galvanised materials, tire wear and the use of
2814
S. SINHA and S. P. BANERJEE
zinc c o m p o u n d in rubber production. Another high loading for SPM, Mn, Cd and Fe were obtained in the second factor which was 37.40% of the total variance. A high correlation coefficient was found between these elements. High factor loading and good correlation coefficient of these elements indicated the association of Mn, Cd and Fe with soil/iron ore sources.
4. CONCLUSIONS The following conclusions are made on the basis of the investigation conducted in N I O M : 1. The particle size distribution of airborne dust emanating from the haul road of N I O M was found to be log-normally distributed. About 60% of the total S P M was found to be within the 0-10/~m size range (PM-10). 2. The free silica content for five different size ranges of airborne haul road dust was found to be varying from 1.1 to 1.3%. The free silica content was found to be slightly higher in the finer size fraction of the particulate matter. 3. The concentration of Pb was observed to be marginally higher than the prescribed ambient air quality standard of U S E P A , but concentrations for all trace elements were found to be less than the prescribed threshold level values of U S E P A . The concentration of Pb was found to be lower than the National ambient air quality standard (India) of 1.5 # g m -3 for industrial area. 4. An E F value less than or equal to unity for Fe, Cd and M n indicated the sources as the earth's crust. An E F value slightly higher than unity was observed for Ni and Cu, whereas Co, Zn and Pb have been found highly enriched and these might have been contributed by anthropogenic sources. 5. The study of factor analysis to determine the sources of trace elements have indicated four major sources which appear to contribute trace elements to total particulate load. These are wind borne soil/road dust (SPM, Mn, Cd, Fe), vehicle exhaust (Pb), metallic corrosion (Cu, Ni), galvanized material, tire wear and zinc c o m p o u n d in rubber material (Zn). Acknowledgements--Financial support for carrying out this study from the Ministry of Environment and Forests, Govt. of India and Tata Iron and Steel Co., OMQ Division, is gratefully acknowledged. The authors are thankful to the authorities of Noamundi Iron ore mines, TISCO for permission to collect information and make measurements in their mines.
REFERENCES Cartwright, J. (1967) Airborne dust in coal mines: the particle-size-selection characteristics of lung and the diserable characteristics of dust-sampling instruments. In Inhaled Particles and Vapours II (edited by Davies C.), pp. 393-406. Pergamon Press, London. Fergusson, J. E. and Kim, N. D. (1991) Trace elements in street and house dusts: sources and speciation. The Science of the Total Environment 100, 125-150. Gaarenstroom, P. D., Perone, S. P. and Moyers, J. L. (1977) Application of pattern recognition and factor analysis for characterisation of atmospheric particulate composition in southwest desert atmosphere. Environment Science and Technology 11,795-800. Hopke, P. K., Gladney, E. S., Gordon, G. E., Zoller, W. H. and Jones, A. G. (1976) The use of multivariate analysis to identify sources of selected elements in the Boston urban aerosols. Atmospheric Environment 10, 1015-1025. Hopke, P. K., Lamb, R. E. and Natuach, E. S. (1980) Multielemental characterisation of urban roadway dust. Environment Science and Technology 14, 164-172. Janssens, M. and Dams, R. (1973) Analitica Chemica Acta, 65, 41. Janssens, M. and Dams, R. (1974) Analitica Chemica Acta 70, 25. Kotrappa, P. (1972) Shape factors for aerosols of coal, UO2 and TiO2 in respirable size range, assessment of airborne particles. Proceedings of the 3rd Rochester International Conference on Environmental Toxicity, Rochester, New York. Mason, B. (1966) Principles of Geology, 3rd Edn. Wiley, New York. Negi, B. S., Sadasivan, S. and Mishra, U. C. (1987) Aerosol composition and sources in urban areas in India. Atmospheric Environment 21, 1259-1266. Ohta, S. and Okita, T. (1990) A chemical characterisation of atmospheric aerosols in Sappro. Atmospheric Environment 24, 815-822. Sadasivan, S. and Negi, B. S. (1990) Elemental characterisation of atmospheric aerosols. The Science of the Total Environment 96, 269-279. Sastry, B. S., Roy, S. C. and Mishra, G. B. (1994) Respirable dust concentration--A case study for a group of mines and crushing plants. In Proceedings of the International Symposium on the Impacts of Mining on the Environmental Problems and Solutions (edited by Paithankar A. G.). VRCE, Nagpur, India. Sax, N. O., Richard, J. and Lewis, S. R. (1986) Hazardous Chemicals in the Working Place. Van Nostrand Reinhold, New York. Sharma, P. K. (1991) Investigation on air quality assessment in some coal mining areas of Raniganj coalfield of India. Ph.D. thesis, ISM, Dhanbad, India. Stevens, R. K. and Pace, T. G. (1984) Overview of the mathematical and emperical receptor models workshop (Quil Roost II). Atmospheric Environment 18, 1497-1500. Talvitie, N. A. (1951) Analytical Chemistry 23, 623. Thakur, P. C. (1974) Mass distribution of respirable dust particles from U.S. coals. Colliery Guardian 222, 236-239. Ministry of Labour, Government of India (1961) The Metalliferous Mines Regulations. Tinsley, D. A., Baron, A. R., Critchley, R. and Williamson, R. J. (1983) International Journal of Environmental Analytical Chemistry 14, 285.