Inhalation Exposure in Secondary Aluminium Smelting

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1 Ann. occup. Hyg., Vol. 45, No. 3, pp , 2001 Crown Copyright 2001 Published by Elsevier Science Ltd on behalf of British Occupational Hygiene Society All rights reserved. Printed in Great Britain /01/$20.00 PII: S (00) Inhalation Exposure in Secondary Aluminium Smelting J. HEALY *, S. D. BRADLEY, C. NORTHAGE and E. SCOBBIE Health and Safety Executive, Magdalen House, Stanley Precinct, Bootle L20 3QZ, UK; Health and Safety Laboratory, Broad Lane, Sheffield S3 7HQ, UK Inhalation exposure at seven UK secondary aluminium smelters was investigated to quantify the main exposures and identify their sources. The substances monitored were gases (carbon monoxide, hydrogen sulphide and nitrogen dioxide), total inhalable dust, metals, ammonia, polycyclic aromatic hydrocarbons (PAHs), particulate fluoride salts and acids. The results showed that people were exposed to a range of workplace air pollutants. Personal exposure results for total inhalable dust were between 700 and 5600 mg m 3 and the maximum personal exposure result for particulate fluoride salts was 690 mg m 3 (as F). The maximum aluminium, total PAH and lead personal exposure results were 900, 19 and 18 mg m 3 respectively. The average proportion of aluminium in total inhalable dust samples was 13% and rotary furnace processes generated the most dust. Particulate fluoride salt exposure was more widespread than hydrofluoric acid exposure. The source of the salt exposure was fluoride containing fluxes. The lead exposure source was lead solder contamination in the furnace charge. Crown Copyright 2001 Published by Elsevier Science Ltd on behalf of British Occupational Hygiene Society. All rights reserved Keywords: aluminium; ammonia; fluoride; lead; PAH; secondary aluminium; inhalable dust INTRODUCTION Production of secondary aluminium is increasing in the UK. Secondary production, predominantly from old scrap, increased steadily from t in 1988, to t in 1995 (Aluminium Federation, 1998). The increase in wrought remelt production, mainly from recycled scrap from fabrication, over the same period rose from to t (Aluminium Federation, 1998). Examples of old scrap include old engines, window frames and road signs. This usually goes via scrap dealers to the secondary smelter and is likely to be contaminated. Scrap from fabrication goes directly to the smelter and is less likely to be contaminated. A significant incentive for recycling aluminium is that scrap melting takes only 5% of the energy required for primary production (Hoyle, 1995). Langer (1998) recently suggested that workers employed in secondary smelters may be exposed to Received 17 April 2000; in final form 10 July *Author to whom correspondence should be addressed. Tel.: ; fax: ; john. healy@hse.gsi.gov.uk a complex of new agents. The source of these exposures may include the thermal degradation products of polyvinyl chloride (PVC), lubricants or petrol modifiers. These are sometimes present in the aluminium feed stock as the coating of wires in the case of PVC and residues in car engines for lubricants and petrol modifiers. Langer (1998) concluded that the exposures experienced during secondary aluminium processing only partially resemble exposures associated with primary aluminium production. There have been few reports of exposure monitoring at secondary aluminium smelters. Inhalable dust, metal concentrations and heat stress monitoring were carried out at a US smelter in 1995 (Kiefer and Salisbury, 1995). The work was conducted as a response to an employee reporting adverse health effects including tingling in the fingers, nausea and dizziness. More recently, Westberg and Selden (1999) reported the preliminary results of some metal determinations at a Swedish facility. There have been a number of recent studies investigating the emissions of various pollutants during the secondary aluminium smelting process. Some of the studies were laboratory-scale investigations which quantitatively determined the species present 217

2 218 J. Healy et al. in flue gases. Other investigations concentrated on the emissions from secondary aluminium smelters. The pollutants identified in these studies were chlorinated organic compounds (Laue et al., 1994; Aittola et al., 1993; Westberg and Selden, 1997), organic compounds containing chlorine and sulphur (Sinkkonen et al., 1994) polycyclic aromatic hydrocarbons (PAHs) (Aittola et al., 1993; Westberg and Selden, 1997; Wei, 1996), acids (Westberg and Selden, 1997) carbon monoxide (Westberg and Selden, 1997) and ammonia (Laue et al., 1994). It was against this background that we carried out an exposure survey at seven UK secondary aluminium smelters. The substances monitored were gases, inhalable dust, metals, ammonia, PAHs, particulate fluoride salts and acids. The aims of the study were to quantify the main exposures and identify their sources. MATERIALS AND METHODS Processes and chemical exposures Seven UK secondary aluminium smelters were surveyed between August and November The amount of aluminium cast by the smelters was between 80 and 700 t per week. The quality of the scrap used varied. Details regarding the smelters are summarised in Table 1. Furnaces operated in the range C. Generally, induction furnaces were used for the least contaminated scrap while relatively contaminated scrap and dross were melted in rotary furnaces. Reverberatory furnaces were mainly used for melting pure scrap and holding furnaces were charged with molten aluminium from other furnaces. Scrap contaminated with iron or steel was melted in sloping hearth furnaces. The exceptions in this study were two induction furnaces and one reverberatory furnace which were used for melting impure scrap. Either one or two people usually worked at the same furnace throughout the shift. Based on observations made during the survey, fume and dust exposures appear to be a number of short-term, relatively high exposures, interspersed with longer periods of lower exposure. The most significant fume and dust exposures were observed during the following operations: Charging furnaces. Typically, rotary and sloping hearth furnaces were charged once or twice per shift and induction furnaces were charged up to four times per shift. During melting, contaminated scrap produces more dust and fume than pure scrap. Scraping the walls of induction furnaces prior to transferring to holding furnaces or casting. Skimming dross from the surface of molten aluminium prior to transferring or casting. The hot dross continues to fume for some time. Some smelters recover aluminium from hot dross by applying pressure to the dross in a dross press. Slagging out rotary furnaces after molten aluminium has been transferred or cast. Elemental sodium addition. The addition of 2.5 kg of sodium to 10 t of molten aluminium alloy in a holding furnace was seen at one smelter only. The operation occurred once per shift, just prior to casting. Blowing nitrogen through molten alloys to ensure a homogeneous melt and bring dross to the surface. This operation was mostly seen at holding furnaces, prior to casting. Local exhaust ventilation (LEV) was used at all furnaces. In most cases a canopy type receptor hood was situated above the front of the furnace, above the charging point. Seventy-five percent of induction furnaces had moveable LEV which was moved during tipping and wall scraping. General ventilation was provided in all premises by large open doors. Twentyone percent of furnaces were within a couple of metres of these doors, which may have helped control exposure. Respiratory protective equipment (RPE) use was not widespread. A powered respirator was used by two people (at different smelters) during induction furnace wall scraping. Filtering half mask respirators were used by two people at two smelters for specific tasks only. The tasks were skimming dross off a sloping hearth furnace and charging, stirring and skimming dross off a reverberatory furnace. The maximum time RPE was used was typically less than half an hour per shift. Sampling and analytical methods With the exception of site number 1, which had approximately 10 people exposed per shift, the sites had between three and five people exposed (Table 1). Given the relatively small number of people exposed at each site it was possible to obtain personal exposure results for most of the workers. The majority of personal sampling results in this paper represent exposures averaged over around 5 h. Gases Carbon monoxide, hydrogen sulphide and nitrogen dioxide were monitored at each smelter with a portable, direct-reading instrument. The instrument, which sampled workplace air by diffusion, was obtained from Neotronics (Hertfordshire UK). Inhalable dust Quartz membrane filters held in Institute of Occupational Medicine (IOM) samplers were used to sample personal and static total inhalable dust at a flow rate of 2 min 1. Sampling and analysis were carried out according to Methods for the Determination of Hazardous Substances (MDHS) 14/2 (HSE, 1997a).

3 Inhalation exposure in secondary aluminium smelting 219 Table 1. Secondary aluminium smelter furnace details Site code No. furnaces Typical scrap quality Approximate no. Approximate number exposed per shift amount of aluminium cast (tonnes per day) Rotary Sloping Induction Reverberatory Holding hearth Rotary furnace oil contaminated swarf Sloping hearth furnace scrap with a high (typically 20%) iron content. Induction furnaces car wheels, dried swarf and ingots. Holding furnaces -molten aluminium from rotary and induction furnaces Induction furnaces and reverberatory furnace mostly clean with some surface lacquer. Holding furnaces molten aluminium from induction and reverberatory furnaces Rotary furnaces -mostly aluminium dross a 4 40 Reverberatory furnace cast aluminium sows from rotary furnaces Sloping hearth furnace scrap with a high iron content 3 20 Reverberatory furnace -scrap contaminated with plastic Holding furnaces molten aluminium from reverberatory furnace Induction furnaces swarf cans and engine radiators Also some foil and ingots Sloping hearth furnaces contaminated scrap including 4 40 window frames, sign posts and lamp posts Induction furnace charge less contaminated than sloping hearth furnace charge; mainly engine blocks Rotary furnaces fragmented dross a accounts for 80% of 4 20 the charge. a Dross forms on the surface of molten aluminium and consists of aluminium oxide and entrained aluminium. It also contains smaller amounts of aluminium nitride, aluminium carbide and magnesium oxide (Stanley and Haupin, 1992).

4 220 J. Healy et al. Metals The metals determined were chromium, manganese, iron, cobalt, nickel, copper, zinc, lead and aluminium. Quartz filters used for sampling inhalable dust were cut in half after weighing. Metals and nonvolatile PAHs were estimated from the resulting samples. Each metals sample was digested in a microwave oven at 30 bar and 210 C in hydrofluoric acid (1 ml) hydrochloric acid (2 ml) and nitric acid (2 ml). After cooling, the solution was diluted to 20 ml and analysed using inductively coupled plasma mass spectrometry. Aluminium was determined using inductively coupled plasma atomic emission spectrometry. Acids Air was drawn through sorbent tubes containing washed silica gel (SKC Ltd, Dorset UK) at 200 ml min 1. National Institute of Occupational Safety and Health method 7903 (NIOSH, 1994) was followed for desorption and analysis by ion chromatography. Particulate fluoride salts MDHS 35/2 (HSE, 1998a) was followed for fluoride salt sampling onto mixed cellulose ester membrane filters at a flow rate of 200 ml min 1 with subsequent analysis by fluoride ion-selective electrode. RESULTS Ammonia Sorbent tubes containing carbon beads impregnated with sulphuric acid (SKC Ltd, Dorset UK) were used for sampling ammonia in air at a flow rate of 200 ml min 1. Desorption and analysis using ion chromatography were carried out according to Occupational Health and Safety Administration Method ID 188 (OSHA, 1991). PAHs PAHs were sampled at a flow rate of 2 min 1 onto quartz membrane filters mounted in IOM samplers backed up with sorbent tubes containing XAD-2 resin. Non-volatile PAHs were trapped by the filter and volatile PAHs were trapped on the sorbent tube. Filters were cut in half and analysed for metals and non-volatile PAHs. PAHs sampled onto the filters and sorbent tube were separately extracted into dichloromethane. The solutions were filtered and analysed by gas chromatography with mass spectrometric (selected ion monitoring) detection. Full sampling and analysis details have been reported elsewhere (Scobbie and Cocker, 1999). The PAHs determined were: naphthalene acenaphthylene acenaphthene fluorene phenanthrene anthracene fluoranthene pyrene benz(a)anthracene chrysene benzo(b)fluoranthene benzo(k)fluoranthene benzo(a)pyrene indeno(1,2,3-c,d)pyrene dibenz(a,h)anthracene benzo(g,h,i)perylene anthanthrene Exposures Personal exposure data obtained from seven UK secondary aluminium smelters are summarised in Table 2. Mean results for data sets containing results that were less than the limit of detection (LOD) in this and other Tables were calculated by replacing these results with LOD/ 2 (Hornung and Reed, 1990). The ranges of area exposure results for carbon monoxide were less than 1 43 ppm at smelter 4, less than 1 30 ppm at smelter 5 and less than 1 ppm at other smelters. The carbon monoxide concentration was highest in the casting area of smelter 4. This was adjacent to an 11 tonne holding furnace. The exposure reached its peak and then decreased over about 4 h. The peak result obtained at smelter 5 lasted for around 2 min during scraping the walls of an induction furnace. Hydrogen sulphide and nitrogen dioxide exposure results were less than their limits of detection at all smelters. The limits of detection were 0.5 ppm for hydrogen sulphide and 1 ppm for nitrogen dioxide. The mean inhalable dust exposure result was 4200 µg m 3. However, this result appears to be skewed by a single high value of µg m 3, because the next highest result was 5600 µg m 3. In addition, the high exposure result was recorded for one member of a team of two and the other member had an exposure result of 2300 µg m 3. Excluding this outlier, the mean personal exposure result is 2600 µg m 3. A scatter plot of the personal inhalable dust results (excluding the single outlier), illustrating their distribution at each smelter, is shown in Fig. 1. The personal inhalable dust results grouped by furnace/process are presented in Table 3. The number of samples in each category in Table 3 is small and so any conclusions are tentative. However, the results suggest that exposure to inhalable dust may be lowest during casting and highest during operations associated with rotary furnaces. Visual observations made during the visits support this conclusion. The aluminium results follow a similar trend. For casting and rotary furnace operations the mean

5 Inhalation exposure in secondary aluminium smelting 221 Table 2. Summary of personal sampling results Pollutant No.of samples Mean sampling time Range of results Mean result (µg m 3 ) (min) (µg m 3 ) Inhalable dust ,200 Aluminium Ammonia and Total PAHs Particulate fluoride salts (as F) Hydrofluoric acid (as F) a 31 Hydrochloric acid a 11 Sulphuric acid All results Iron Zinc Lead Chromium Copper Nickel Manganese Cobalt a Only one result was above the limit of detection. ters. Slightly more surprising are lead exposures. Personal aluminium and lead exposure results at the various smelters are illustrated in Fig. 2 and 3 respectively. The mean of the personal and static results from smelter 6 was 12 µg m 3. This is higher than the Fig. 1. Scatter plot of personal inhalable dust results. personal aluminium results were 60 and 490 µg m 3 respectively. The mean personal aluminium results for the operations sampled at sloping hearth, induction and reverberatory/holding furnaces were in the range µg m 3. As might be expected, aluminium is the most abundant pollutant metal in the workplace atmosphere of secondary aluminium smel- Fig. 2. Scatter plot of personal aluminium results. Table 3. Personal inhalable dust exposure by furnace/process Furnace/process No. of samples Range of results (µg m 3 ) Mean result (µg m 3 ) Rotary Sloping hearth Induction Reverberatory/holding a 2400 a Casting and a Excluding outlying result of µg m 3.

6 222 J. Healy et al. Fig. 3. Scatter plot of personal lead results. Fig. 4. Scatter plot of personal total PAH results. range of the same means from the other smelters, which was between 0.1 and 6 µg m 3. Only two personal ammonia samples were taken and the results are shown in Table 2. The result of 80 µg m 3 was for a person who spent around 30% of the shift pressing and moving dross. Other activities were charging relatively pure scrap into a reverberatory furnace (30% of shift) and breaks (30% of shift). The result of 260 µg m 3 was for a person who divided his time approximately equally between induction furnace operations (charging, wall scraping etc) and ingot stacking. A dross press was situated about 10 m from the furnace. Static samples were also taken at each of the smelters. The range of results from 23 samples was less than µg m 3. Eighty seven per cent of the results were greater than the limit of detection. From a total of 25 personal and static ammonia results, the results from smelter 3 exceeded all other results. There were three results (all static samples) and their range was from 260 to 1300 µg m 3. The proportion of volatile PAHs nearly always exceeded the proportion of non-volatile PAHs in both personal and static samples. The main PAH in all samples was naphthalene. The personal exposure results obtained are shown in Fig. 4. There is one noticeably high personal total PAH result of 19 µg m 3. This person worked at a (tilting) induction furnace. During the sampling period there were 2 10 min pouring periods, 15 min blowing with a nitrogen/argon mixture and the rest of the time was spent preparing and charging 3.4 t of scrap and casting. There was nothing unusual in this shift pattern and so we are unable to account for this high result. The next highest personal exposure result was 8 µg m 3. The remaining total PAH results, either personal or static samples, did not exhibit any discernible trend when grouped by smelter or furnace. The range of personal exposure results for naphthalene were from 1 to 10 µg m 3, with a mean of 2 µg m 3. Benzo(a)pyrene personal exposure results were between 0.01 and 0.4 µg m 3, with a mean of 0.1 µg m 3. Twelve personal acid exposure samples were taken and hydrofluoric, hydrochloric and sulphuric acid concentrations were determined from each sample. All of the sulphuric acid results and 11 out of 12 hydrofluoric and hydrochloric acid results were less than the limit of detection. All static hydrofluoric acid samples results (N=23) were less than the limit of detection. Only 4 out of 23 static hydrochloric acid samples were above the limit of detection. The range of these results was between 40 and 1400 µg m 3. Twenty three static sulphuric acid samples were taken. Five were greater than the limit of detection and these results were between 60 and 180 µg m 3. The results of personal fluoride salt determinations are illustrated in Fig. 5. Personal samples were not taken at smelters 3 and 7. The results for three static samples at smelter 3 were all less than the limit of detection. The range of Fig. 5. Scatter plot of personal particulate fluoride salt results.

7 Inhalation exposure in secondary aluminium smelting 223 results from four static samples at smelter 7 were from less than the limit of detection to 90 µg m 3. DISCUSSION Kiefer and Salisbury (1995) used a direct reading instrument to measure carbon monoxide levels. They found concentrations in a US smelter were less than 4 ppm, with the exception of one measurement of 14 ppm at an ingot stacking station. This exposure was attributed to propane-powered rider operated lift trucks. We believe that the peak carbon monoxide results of 30 and 43 ppm at two smelters in this survey were probably due to incomplete combustion of contaminants in the furnace charge and inadequate ventilation. The average proportion of aluminium present in personal and static inhalable dust samples was 13%. From a total of 33 results, this proportion varied between 5 and 27%, with a standard deviation of 5%. If it is assumed that aluminium is present as the oxide, the average proportion of Al 2 O 3, in the dust sampled was 25%. The composition of the remaining 75% of the dust is uncertain, although the metals analysis (Table 2) suggests that other metal oxides alone cannot account for the shortfall. The source of lead in the samples is probably lead solder contamination in the furnace charge. The material used for copper additions at smelter 6, where the mean of personal and static lead results was 12 µg m 3, was short lengths of copper pipe with lead soldered joints. The amount of lead contamination in the furnace charge is probably relatively small. However, the melting point of lead is around half the melting point of aluminium and is significantly less than the melting points of other metals determined in this survey. Secondary aluminium smelting therefore takes place at temperatures at which lead will become volatile and hence the high exposure relative to the degree of contamination. The relatively high ammonia results at smelter 3 were attributed to a large dross storage area which was around 50 m from the samplers. The odour of ammonia was very strong in this storage area. The origin of ammonia is most commonly from dross stored outside the foundry buildings. Dross contains aluminium nitride which liberates ammonia on contact with water. The typical range of aluminium nitride concentration in waste drosses for recovery is 5 14% (Hymes, 2000). The source of PAHs in this study was considered to be the thermal degradation of organic contaminants in the furnace charge. PAH exposure is a concern because some PAHs are known carcinogens (HSE, 1997b). As far as we are aware, this is the first time occupational PAH exposure results have been reported in secondary aluminium smelters. Primary aluminium smelters are known to produce PAHs from preparation or consumption of carbon anodes, but this process is not found in secondary smelters. As a point for comparison, HSE recently carried out a survey of PAH exposure in various UK industries (Scobbie and Cocker, 1999). Median total PAH concentrations at 25 sites ranged from 2 to 880 µg m 3. The median total personal PAH concentration in this study was 3 µg m 3, which would place secondary aluminium smelting at the lower end of those sampled. Twelve personal hydrofluoric acid samples were taken. Eleven of these were less than the limit of detection and 1 result was 290 µg m 3. The only possible source of hydrofluoric acid for the single result greater than the detection limit was from the use of a flux containing sodium fluorosilicate, sodium carbonate and aluminium fluoride. However, during the monitoring period only around 500 g of the flux was added to an induction furnace under LEV. Other fluxes encountered during the survey were potassium aluminium fluoride, sodium fluorosilicate, calcium fluoride, potassium chloride, sodium chloride and potassium carbonate. The hydrochloric and sulphuric acid personal exposure results indicate a low level of exposure to these acids. The highest static hydrochloric acid result (1400 µg m 3 ) was for a rotary furnace melting dross. Two melts of around 1.5 t were carried out during the sampling period. Three hundred kg of flux was used per melt. The flux was a mixture of sodium chloride (69%), potassium chloride (29%) and calcium fluoride (2%). It was added to the furnace by shovel over a few minutes per melt. Ten out of 12 personal fluoride salt results were greater than the limit of detection, which suggests that exposure to fluoride salts is more likely than hydrofluoric acid exposure. The source of the exposures is fluoride containing fluxes. The highest exposure result of 690 µg m 3 was a result of manually tipping around 200 kg of potassium aluminium fluoride into the launder between an induction and a holding furnace while transferring molten aluminium alloy. The purpose of the addition was to reduce the magnesium concentration of the alloy. This operation lasted for a few minutes and was conducted without LEV. RPE was not used. A comparison between some metal exposure results obtained in this study with results obtained in Swedish (Westberg and Selden, 1999) and US (Kiefer and Salisbury, 1995) smelters is shown in Table 4. Comparison of this study s results with the Swedish and US studies shows that aluminium results appear higher in the smelters sampled in this study. Lead results are higher than in the US study and in the same range as the Swedish work. Manganese exposures are approximately equivalent. However, given the limited database of results it is not possible to draw any firmer conclusions. A number of the workplace air pollutants found during this survey have occupational exposure limits (OELs). A comparison between the highest exposure

8 224 J. Healy et al. Table 4. Comparison of selected metal at different smelters Aluminium Lead Manganese N Range Mean N Range Mean N Range Mean (µg m 3 ) (µg m 3 ) (µg m 3 ) (µg m 3 ) (µg m 3 ) (µg m 3 ) This study Swedish study a ns ns b US study All a Mainly personal exposures. b Geometric mean; ns=not stated. Table 5. Highest personal sampling results compared with occupational exposure limits for Great Britain (HSE, 2000) Pollutant 8-h time weighted average occupational Highest result as a percentage of exposure limit (µg m 3 ) limit value Inhalable dust a 56 b Particulate fluoride salts (as F) 2500 c 28 Hydrofluoric acid (as F) 2500 c d 12 e Lead 150 f 12 Aluminium c 9 Chromium 500 c 3 Ammonia c 1 Nickel 500 g 1 a If above a concentration of µg m 3, inhalable dust becomes a substance hazardous to health for the purpose of the COSHH Regulation (HSE, 1999). b Excluding the result of µg m 3, which is regarded as an outlier. c Occupational exposure standard. d Short-term exposure limit (15-min reference period). e Most results (92%) were less than the limit of detection. f Occupational exposure limit for the purposes of the Control of Lead at Work Regulations (HSE, 1998b). g Maximum exposure limit. results and their OELs, as defined in Great Britain (HSE, 2000) is presented in Table 5. With the exception of hydrofluoric acid, the comparison assumes that the exposure results obtained in this survey (average sampling time around 5 h) are equivalent to 8-h time weighted average exposures. Exposure results which are less than 1% of their OEL are excluded. The comparison between measured exposure results and the current statutory controls for Great Britain shows that: Exposure up to around 10% of the OEL is possible for lead and aluminium. Particulate fluoride salt exposure can reach nearly 30% of the OEL and Exposure to inhalable dust is nearly 60% of the level defined in the COSHH Regulations as a substance hazardous to health (HSE, 1999). This paper outlines the results of air sampling at seven secondary aluminium smelters, an area which was not well characterised. Although none of the substances measured approached the OELs set in Great Britain, this study indicates that the main exposures are dust, fluoride salts, lead and aluminium. However, we cannot exclude the possibility of other exposures. Possible examples include cadmium (from cadmium plated fasteners on engine blocks and heads) and polychlorinated organic compounds (Aittola et al., 1993). The finding of PAHs on sampling in this industry should also be noted. The main interactions (if any) between components of a mixed exposure are either synergistic, additive or independent effects (HSE, 2000). A review of the toxicological data for each of the substances identified in this survey is required to assess if there are any interactions. Such a review is beyond the scope of this work. Acknowledgements We wish to thank the smelters for their co-operation with this survey, Nick Williams (HSE) for preparing the figures for the manuscript and colleagues who commented on the work. REFERENCES Aittola J-P, Paasivirta J, Vattulainen A. Measurements of organochloro compounds at a metal reclamation plant. Chemosphere 1993;27: Aluminium Federation. Annual report of the Aluminium Federation for the year Birmingham: Aluminium Federation Ltd; 1998.

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