Annals of Occupational Hygiene Advance Access originally published online on July 7, 2004
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Ann. occup. Hyg., Vol. 48, No. 5, pp. 405-414, 2004
© 2004 British Occupational Hygiene Society
Published by Oxford University Press
A Survey of Airborne Isocyanate Exposure in 13 Swedish Polyurethane Industries
1 Department of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden; 2 National Institute for Working Life North, Department of Work and the Physical Environment, PO Box 7654, SE-907 13 Umeå, Sweden
Received 15 September 2003; in final form 22 December 2003; published online on 7 July 2003
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Exposure to isocyanates can be harmful to workers by causing different disorders of the airways. The main objectives of this study were to survey the personal 8 h time-weighted average exposure to isocyanates at 13 Swedish plants that handled either polyurethane, diisocyanates or both, including four types of manufacturing processes: moulding, continuous foaming, flame lamination and low or no heating processes. A total of 223 air samples were collected for 111 workers with personal air monitoring using a dry filter method with 1-(2-methoxyphenyl)piperazine (2MP) as derivatization reagent. A further 272 stationary samples were collected, using the 2MP method, a modified 2MP method and an impinger method using dibutylamine in toluene. With the applied strategy, a large number of workers were monitored and four industrial environments were compared regarding the isocyanate exposure. All workers were found to be exposed to isocyanates in the range 0.004–5.2 p.p.b. On average, the personal exposure levels in the different types of manufacturing processes were, in decreasing order: continuous foaming > flame lamination > moulding >> low or no heating processes. However, there were variations in exposure levels in plants with similar processes and also between different shifts performing the same tasks. Isocyanic acid, which could not be sampled by the 2MP method used for personal monitoring, was found by short-term stationary monitoring in levels up to 38 p.p.b. in the flame lamination plants.
Keywords: diisocyanates; occupational exposure
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Occupational exposure to isocyanates may occur in various working environments where polyurethanes (PUR) are manufactured or processed. Isocyanates can be harmful to exposed workers, causing different acute and chronic respiratory symptoms such as asthma-like symptoms, occupational asthma and rhinitis and hypersensitivity pneumonitis (Vandenplas et al., 1993; Baur et al., 1994). Many industrially developed countries have established exposure limits for the work environment. In Sweden, where this study was performed, the occupational exposure threshold limit (OEL) is general for all isocyanates and is at present 5 p.p.b. for an 8 h time-weighted average (TWA), while the short-term exposure limit (STEL) is 10 p.p.b. for a 5 min TWA. In other countries, such as Finland and the UK, the exposure limits are based on the total reactive isocyanate groups (TRIG) in air, while in Germany and the USA the exposure limits are given for each individual isocyanate. Exposure assessment of isocyanates is complex, since these substances are reactive and occur in both the gas and particle phases. Furthermore, during thermal degradation of PUR, a mixture of isocyanates is formed, including the low molecular weight methyl isocyanate (MIC) and isocyanic acid (ICA) (Karlsson et al., 2002), making the assessment even more complex. Several methods for air monitoring of isocyanates have been reported and these have been reviewed, for example by Streicher et al. (2000). In this study we have applied the ‘2MP method’ (Health and Safety Laboratory, 1999; Östin et al., 2002) using 1-(2-methoxyphenyl)piperazine (2MP) impregnated filters for assessment of the personal 8 h TWA exposure for workers in different types of industries. Stationary monitoring was performed, using the 2MP method and two other methods. The ‘FINMP method’ (Henriks-Eckerman et al., 2000), using 2MP impregnated double filters, was mainly used to monitor the air levels of MIC and ICA, which could not be determined by the 2MP method. The ‘DBA method’ (Spanne et al., 1996; Karlsson et al., 2000), an impinger method with a filter in series, using dibutylamine (DBA) as derivatization reagent, was mainly used for the evaluation of the 2MP method. The evaluation of the 2MP method field performance is presented in another study (Sennbro et al., 2004).
The main objective of this study was to survey the 8 h TWA exposure to 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), isophorone diisocyanate (IPDI), 4,4'-methylenediphenyl diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI) and phenyl isocyanate (PI) for occupationally exposed workers in 13 Swedish PUR industries by personal monitoring, including different types of industrial processes.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Survey strategy
Plants located in the southern part of Sweden, and where PUR, isocyanates or both were used by at least three employees, were selected for monitoring of isocyanate exposure. Apart from cross-sectional surveillance, 8 h TWA exposures were also used for the validation of biomarkers (Sennbro et al., submitted). Through evaluations of an earlier assessment report (Norén, 2000), 15 plants with the highest expected exposures to isocyanates were selected and out of those 13 plants agreed to participate in the study. Personal monitoring was performed on those workers who performed their daily tasks in contact with isocyanates or heated PUR at these plants. In total, 111 out of 162 possible workers at the selected plants were monitored. Some individuals did not agree to participate and at some plants the workers on the evening and night shifts were not invited to participate if their exposure was considered to be similar to the monitored workers. In cases of insufficient equipment, the workers in the shift were randomly excluded from participation. The study was performed from April 2000 to May 2001. The study was approved by the Ethical Committee at Lund University, Sweden, and was performed on a voluntary basis with the written informed consent of the workers.
Description of the plants
The study included 13 plants using four different types of manufacturing process: moulding, continuous foaming, flame lamination and low or no heating processes. A comprehensive description of the plants is presented below and an overview of the isocyanates used, the number of workers monitored and the number of samples collected in the plants are given in Table 1.
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Moulding plants (M1–M7)
Plant M1
Plant M1 manufactured NDI- and MDI-based rigid PUR products by moulding and centrifugal moulding. The dosing, mixing and moulding of the PUR were performed manually, partly in ventilated hoods. After hardening of the products overnight, the PUR material was refined by grinding and turning. Of a total of eight workers, five participated in the study, two workers were absent on the day of sampling and one worker did not agree to participate. Sampling was performed during one shift and the production load was normal.
Plant M2
Plant M2 manufactured mainly NDI- but also MDI-based rigid PUR products by moulding. The dosing, mixing and moulding of the NDI-based products were performed automatically in a semi-enclosed ventilated area. Within this area, preparation of the moulding matrices and transfer of the ready-made products into the hardening furnace during the manufacturing process was performed. Outside the semi-enclosed area, preparation and sorting of the moulding matrices was performed. The MDI products were only manufactured as prototypes in a pilot system in a separate area. Personal protection equipment (PPE) was used occasionally. The work in the department was organized with 12 workers in two shifts, morning (a.m.) and afternoon (p.m.), alternating every second week. In each shift, one worker was the head operator, one worked outside the semi-enclosed area and four workers shifted between three positions within the semi-enclosed area. All 12 workers participated in the study. Sampling was performed during two shifts and the production load was normal and equal during the two shifts.
Plant M3
Plant M3 manufactured TDI-based (2,4-TDI- and 2,6-TDI) rigid PUR components by moulding. The dosing, mixing and moulding were performed manually in partly ventilated hoods. After hardening of the products, the PUR material was refined by grinding and turning in an adjacent section of the working area. PPE was used occasionally. In plant M3, five workers were directly involved in the dosing, mixing and moulding and two workers mainly refined the PUR products. All seven workers participated in the study. Sampling was performed during one shift and the production load was reported to be higher than normal.
Plant M4
Plant M4 manufactured semi-flexible PUR foam blocks by moulding. The isocyanates used were mainly TDI, but MDI and IPDI were also used. The manufacturing process was divided into two steps. In the first step, the ingredients were mixed and then moulded in an enclosed system. After hardening, the PUR blocks were manually removed from the matrices, washed and then transferred to another section of the working area. In this area, the PUR blocks were expanded in a heated water bath. When work was performed within the closed area, PPE was used. The workers rotated in a continuous six-shift scheme with six men in each shift. Within each shift, during a 6 day working period, three men worked in the expansion area and three men in the moulding area for 3 days then the work tasks were swapped for the subsequent 3 days. Sampling was performed for all six different shifts (a.m.1–3 and p.m.1–3). Nightshifts were not monitored and only 24 out of 36 workers agreed to participate in the study. The production load was normal for four of the shifts and lower for two (a.m.2 and a.m.3), due to production failures.
Plant M5
Plant M5 manufactured TDI- and MDI- based flexible PUR foam components by moulding. The mixing of PUR ingredients and the moulding were performed automatically in an enclosed system. In plant M5, six workers were directly involved in the dosing, mixing and moulding, and three other workers mainly refined the PUR products. All nine workers participated in the study. Sampling was performed during one shift when the production load was normal.
Plant M6
Plant M6 manufactured TDI-based flexible PUR foam components by moulding. The working conditions were similar to plant M5. The workers were divided into daytime workers or into a three shift schedule; a.m., p.m. and nightshift. The number of workers in the production area during daytime was 24, including both daytime and a.m. shift workers. During p.m. and the nightshift the number of workers was six. In total, 16 of the daytime/a.m. shift workers and five of the p.m. shift workers participated in the study. The other workers were not invited to participate. Sampling was performed during two shifts when the production load was normal.
Plant M7
Plant M7 manufactured TDI-based flexible PUR foam components by moulding in a process very similar to that described for plants M5 and M6 above. The workers worked in the daytime and six of ten workers participated in the study. The other workers were not invited to participate in the study. Sampling was performed during one shift when the production load was normal.
Continuous foaming plants (CF1 and CF2)
Plant CF1
Plant CF1 manufactured TDI-based flexible PUR foam in continuous foam blocks. In an enclosed ventilated tunnel system, the PUR foam expanded on moving craft paper and was then cut into pieces. The process was performed intermittently and the workers were only monitored during those periods. PPE was used by workers that performed their tasks close to the foaming head. At this plant, six workers worked daytime and all participated in the study. Sampling was performed during one shift and the production load was reported to be normal.
Plant CF2
Plant CF2 manufactured TDI-based flexible PUR foams in continuous foam blocks in a process very similar to that described for plant CF1 above. The manufacturing process was, however, performed in a semi-enclosed tunnel. As in plant CF1, the monitoring of workers was only performed during the foaming process and PPE was used by personnel working close to the foaming head. At this plant, five workers worked daytime and four participated in the study. The fifth worker was absent on the day of monitoring. Sampling was performed during one shift and production was reported to be normal.
Flame lamination plants (FL1 and FL2)
Plant FL1
Plant FL1 manufactured laminates of textile foils and TDI-based flexible PUR foam sheets by flame lamination. The PUR sheet was melted using an open gas flame and the textile foil was applied and fused. The laminated product was then controlled and refined by cutting. In total eight workers were organized into two shifts (a.m. and p.m.) and all eight workers participated in the study. Sampling was performed during both shifts. Production was lower during the p.m. shift than during the a.m. shift as only one of two flame laminators was in use, but this was the normal procedure.
Plant FL2
Plant FL2 manufactured laminates of textile foil and TDI-based PUR foam sheets by flame lamination as described for plant FL1 above. Some of the ready laminates were transferred to plant LH1 for refinement. Eight workers were organized into a daytime shift. Four workers performed lamination, of which three participated in the study. The fourth worker was absent on the day of sampling. The four workers controlling the laminates did not agree to participate. Sampling was performed during one shift and the production was reported to be less than normal, due to major production and delivery failures.
Plants with low or no heating processes (LH1 and LH2)
Plant LH1
Plant LH1 performed further refinement, i.e. stripping and cutting, of the textile laminates from plant FL2. UV radiation-mediated lamination of textile foils and TDI-based PUR foam sheets was also performed irregularly. None of the monitored personnel worked at the laminator, rather they performed refinement of PUR textile laminates without any heat treatment. No UV-mediated lamination was performed on the sampling day, except for one simulation of 8 min. All workers worked in the daytime and five persons, of a total of eight, participated in the study. The other workers were not invited to participate. Sampling was performed during one shift and production was reported to be normal.
Plant LH2
Plant LH2 manufactured different preparations of TDI- and MDI-based PUR and isocyanate formulations, such as jointing and sealing compound. The monitored workers performed either dosing and mixing of the formulation ingredients or packaging of the completed formulation products. The formulations were treated at a temperature of <40°C. The workers were organized into three shifts. At this plant, three workers on one shift participated in the study. The workers on the other two shifts were not invited to participate. The production load was reported to be normal during the sampling.
Air monitoring methods
Three different methods were used for the monitoring of isocyanates in air. The first method (Health and Safety Laboratory, 1999), referred to as the 2MP method, used single glassfibre filters impregnated with 2MP. The second method, referred to as the FINMP method (Henriks-Eckerman et al., 2000), used double glassfibre filters impregnated with 2MP. For both methods using 2MP the filters were transferred to glass vials containing 2MP reagent in toluene immediately after sampling. The samples were kept away from light and stored in a refrigerator until analysis. The FINMP method was mainly used to study exposure to ICA and MIC. The third method, referred to as the DBA method (Spanne et al., 1996; Karlsson et al., 2000), used impinger flasks containing DBA in toluene in series with a glassfibre filter. Immediately after sampling, the impinger solution was transferred to test tubes and the filter was transferred to a test tube of the same kind containing DBA in toluene. The samples were stored in a refrigerator until analysis. The pumps used in the sampling were Gilair Personal Air Samplers from Gilian Instruments Corporation (West Caldwell, NJ) or Escort Elf Pumps from Mine Safety Appliance Co. (Pittsburgh, PA). GPE Meterate rotameters from Jencons-PLS (Leighton Buzzard, UK), calibrated against bubble meters, were used for air flow rate measurements. The air flow rates (1 l/min) were calibrated prior to sampling and checked during and after sampling. All the collected air samples are summarized in Table 1.
Personal monitoring
Personal monitoring was performed on 111 workers in total. All the workers were monitored on one occasion, except for two workers in plant M7, who were monitored twice. For personal monitoring, the 2MP method was used. An estimation of the 8 h TWA exposure for each worker was performed by sampling one filter for the first 4 h of the shift and one filter for the subsequent 4 h. In plants CF1 and CF2, the exposed workers were considered to be exposed to isocyanates only during the intermittent foaming process and, hence, sampling was performed during these periods only, corresponding to 3–4 h of the working day. Apart from the workers in plants CF1 and CF2 and three workers from other plants that were monitored for only half a day (1 x 4 h), the average total monitoring time for the remaining workers was 7.4 h. In a parallel study, the air levels were compared with levels of biomarkers in urine and plasma samples collected from the workers (Sennbro et al., submitted), in which the sampling was suspended for periods when PPE was used by the workers, since the external exposure was then considered to be zero. An exception was made in plants CF1 and CF2, where suspension was not practically feasible. Suspension of sampling was performed for 1.5 h for one person in plant M2, for 2.5 h for one person in plant M3 and for a total of 10 h for nine persons in plant M4. The variation in personal exposure at the plants was analysed as the coefficient of variance (CV) and the variation between shifts was analysed by the independent samples t-test. For calculations of CV values, plants M1 and LH2 were not considered, since different isocyanates were handled by different workers, nor were plants CF1 and CF2, since some workers used PPE and some not.
Stationary monitoring
Stationary monitoring was performed at all plants as a complement to personal monitoring in order to estimate the emission from different sources, to estimate area levels and also for method comparisons. Of the 272 stationary samples, 237 were also used for method comparisons by parallel sampling, and these results will be presented in another paper (Sennbro et al., 2004). All three air monitoring methods were used for the stationary monitoring with t = 2–266 min. The FINMP method was introduced during the progress of the study and was only applied in plants M3, FL1 and FL2.
Analysis
The 2,4-TDI, 2,6-TDI, IPDI, MDI, NDI and PI levels were analysed by all three methods. With the DBA and FINMP methods, MIC and ICA levels were also included. The analysis of ICA (Karlsson et al., 2001) and MIC using the DBA method was introduced during the progress of the study and was not applied in plants M4 and M5. Standards for quantification of the samples using the 2MP method were prepared according to the procedure described in Health and Safety Laboratory (1999). The deuterated internal standards, which were used for quantification, were prepared in a similar way as their non-deuterated homologues but by small scale synthesis using tri-deuterated 2MP instead of 2MP. Analysis was performed by liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) as described by Östin et al. (2002), except that deuterated internal standards were used. For the FINMP samples, the same analysis procedure as for the 2MP samples was applied. The limit of quantification (LOQ) was 20 ng/sample for each isocyanate.
Standards for quantification of the samples using the DBA method were prepared as described by Karlsson et al. (1998). The deuterated internal standards, which were used for quantification, were synthesized in the same way except that octa-decadeuterated DBA was used instead of DBA. Analysis was performed by LC-MS/MS. The LOQ was 20 ng/sample for ICA and 2 ng/sample for the other isocyanates.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Personal monitoring
Personal 8 h TWA exposure levels and comparison between industrial processes
The 8 h TWA exposure levels for the specific and total isocyanates for the workers at the plants are summarized in Tables 2, 3 and 4. Note that all reported air levels of TDI were not corrected for long-term losses as described in the parallel study by Sennbro et al. (2004). All the monitored workers were found to be exposed to total isocyanates in the range 0.004–5.2 p.p.b. (n = 111, mean 0.72 p.p.b., median 0.39 p.p.b.). Nineteen per cent of the personal 8 h TWA air levels of the total isocyanates were >1 p.p.b. and only one worker had air levels >5 p.p.b., the Swedish OEL. The range of exposure was 0.004–1.9 p.p.b. (n = 82, mean 0.48 p.p.b., median 0.34 p.p.b.) for the moulding plants, 0.61–3.8 p.p.b. (n = 11, mean 1.6 p.p.b., median 1.4 p.p.b.) for the flame lamination plants, 0.08–5.2 p.p.b. (n = 10, mean 2.3 p.p.b., median 2.2 p.p.b.) for the continuous foaming plants and 0.03–0.10 p.p.b. (n = 8, mean 0.06 p.p.b., median 0.05 p.p.b.) for the plants with low or no heating processes.
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Variation of exposure
The calculated CV values for the 2,4-TDI- and 2,6-TDI-exposed workers on different shifts in different plants are shown in Table 5.
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In plant M4, the mean IPDI exposures for the six shifts were 0.01–0.07 p.p.b. (CV = 8–74%). In this plant, two of the shifts (a.m.2 and a.m.3) had lower production loads than the others and on one shift (p.m.3) only one worker participated. The other three shifts, a.m.1, p.m.1 and p.m.2, with normal production loads were compared. The a.m.1 and p.m.1 shifts had significantly higher exposures to 2,4-TDI (P = 0.003 and P = 0.003) and 2,6-TDI (P = 0.003 and P = 0.004) compared with p.m.2, but only a.m.1 had significantly higher exposure to IPDI than p.m.2 (P < 0.001). The a.m.1 and p.m.1 shifts did not differ significantly (P > 0.29) in exposure. For the workers in the expansion area and the workers in the moulding area there were no significant differences in exposure to 2,4-TDI, 2,6-TDI or IPDI (P = 0.86, 0.44 and 0.78, respectively).
In plant M6, no significant differences in exposure to 2,4-TDI (P = 0.48) or 2,6-TDI (P = 0.32) were found between the two shifts.
In plant FL1, the mean PI exposure was 0.12 p.p.b. (CV = 11%) for the p.m. shift and 0.24 p.p.b. (CV = 22%) for the a.m. shift. In this plant, there was a significantly higher exposure for the a.m. shift workers (P = 0.01 for 2,4-TDI, P = 0.02 for 2,6-TDI and P = 0.01 for PI), probably due to the greater activity in the a.m. shift. In FL2, the CV was 57% for the PI exposure.
In plant M2, the mean NDI exposure was 0.3 p.p.b. (CV = 28%) for the a.m. shift and 0.6 p.p.b. (CV = 87%) for the p.m. shift, but there was no significant difference (P = 0.21) between the shifts. The difference is explained by one worker in this shift, the foreman, who had a much higher exposure than the other workers. This worker performed maintenance in high exposure areas without PPE. Apart from his exposure, those for the two shifts were nearly equal (means of 0.3 and 0.4 p.p.b., respectively).
Stationary monitoring
Air levels found by area sampling were of the same order of magnitude as the levels found by personal monitoring, although the levels found close to emission sources were often higher than the corresponding personal levels. The most striking findings from the stationary samplings are presented below.
Mouldings
In plant M2, two samples containing 14 and 23 p.p.b. NDI (t = 18 and 22 min) were found at the end of the hardening furnace, where the workers removed finished products. In these samples, 
3 p.p.b. ICA and 3 p.p.b. MIC were also found. These high levels of NDI exceeded the levels found within the semi-enclosed area and were due to a positive pressure inside the furnace. Emission from the furnace led to distribution of NDI within the factory and 0.3 p.p.b. NDI (t = 148 min) was found in a sample collected 30 m from the furnace.
In plant M4, peak exposures to TDI in the range 5–15 p.p.b. (t = 10–185 min, n = 14) were found in the enclosed area where PPE was obligatory and where workers only performed work intermittently.
The stationary samples taken in plants M5–M7 confirmed the higher exposure levels of TDI found in plant M7 by personal monitoring. The mean TDI levels around the production line were 0.4, 0.2 and 1.1 p.p.b. in plants M5–M7, respectively.
Continuous foaming
The stationary samples collected in plants CF1 and CF2 confirmed the higher exposure levels of TDI found by personal monitoring in plant CF2 compared with CF1. In plant CF1, the TDI levels in the stationary samples around the curing tunnel did not exceed 0.3 p.p.b., while an area sampling 10 m adjacent to the curing tunnel in CF2 showed an air level of 7 p.p.b. TDI (t = 131 min).
Flame lamination
In plants FL1 and FL2, TDI levels up to 27 and 14 p.p.b., respectively, were found in samples collected within 5 m of the flame laminator. Of the 46 samples collected within 5 m of the flame laminators in both plants, 22% had levels >10 p.p.b. (t = 11–200 min).
In plants FL1 and FL2, ICA levels up to 28 and 38 p.p.b., respectively, were found in samples collected within 5 m of the flame laminator. Of the 27 samples collected within 5 m of the flame laminators at both plants, 78% had levels >10 p.p.b. (t = 4–238 min). For the 17 samples collected >5 m of the flame laminators 18% were >5 p.p.b. and none were >10 p.p.b. (t = 16–208 min). The proportion of samples containing air levels of ICA and TDI exceeding 10 p.p.b. in FL1 and FL2 were similar.
The PI levels were <5 p.p.b. in all samples, but considerably higher than the levels determined by personal monitoring. The highest PI level was 4.5 p.p.b. The levels of MIC were <0.2 p.p.b.
The air levels of ICA, PI and TDI in the stationary samplings, sampled by the DBA and FINMP methods in plants FL1 and FL2, are shown in Fig. 1, where the contribution of MIC has been neglected.
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Low or no heating processes
In plant LH1, during a simulation at the UV laminator, 15 p.p.b. TDI, 0.2 p.p.b. PI, 3 p.p.b. ICA and 0.04 p.p.b. MIC (t = 8 min) were found in the breathing zone near the UV laminator. None of the workers monitored in LH1 were working close to the UV laminator, however, but they were probably exposed due to widespread exposure originating from this site in the working area.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The main objective of this study was to survey the personal 8 h TWA isocyanate exposures for workers selected in plants, which beforehand were expected to have relatively high exposures to isocyanates, considering working conditions in Sweden. In the selected plants, we believe that a representative group of workers that directly operate with isocyanates or PUR products have been monitored, but some occupations subjected to intermittent high exposure, such as maintenance workers, were not included. In total 111 workers were monitored and all were found to be exposed to isocyanates in the range 0.004–5.2 p.p.b. The average personal exposure levels for the different types of manufacturing processes were in decreasing order: continuous foaming > flame lamination > moulding >> low or no heating processes. However, there was a variation of exposure levels by a factor of 4 between very similar plants and a variation of exposure by a factor of 3 between different shifts performing the same tasks in one plant. There was also a large variation in exposure between individuals performing the same work at the same plant.
For long-term sampling, as performed in this study, only dry techniques are applicable in practice. Most previous studies reporting personal 8 h TWA exposure assessment of isocyanates have used paper tape methods (Butcher et al., 1977; Omae et al., 1992; Tinnerberg et al., 1997; Meredith et al., 2000) and two have used filter methods (Maitre et al., 1993; Lindh et al., 1997). The paper tape methods are known to be less selective due to interference and are not accurate for quantitative sampling (Levine et al., 1995). In this study we have used filters impregnated with 2MP to collect two consecutive 4 h samples. This was a time-consuming strategy as the personnel performing the study could not monitor more than five workers if they were also to check air flows, perform stationary measurements and control work tasks performed by the workers. A total of 38 man days at the different plants were needed to accomplish this number of whole day measurements. The use of a passive sampling methodology (Batlle et al., 2001) may offer a more cost-effective sampling procedure. In a parallel paper (Sennbro et al., 2004), the long-term efficiency of the 2MP method for TDI was evaluated. The corresponding evaluation for the other isocyanates was not performed. Significant losses of sampled 2,4-TDI and 2,6-TDI were observed during a 4 h sampling, compared with parallel sampling by the same method with shorter sampling times. The results indicate that the measured levels of 2,4-TDI and 2,6-TDI in the present study are underestimates of the true exposure levels. Since this drawback of the method is quantifiable, a correction factor that reduces the inaccuracy in the air measurements has been calculated. However, this correction factor needs to be corroborated in further studies and therefore the uncorrected results are presented here.
The personal exposure levels found indicate that workers in Sweden are seldom exposed above the current Swedish OEL of 5 p.p.b., since this was only observed for one person in this study. However, the levels detected by stationary monitoring close to the emission sources indicate that a divergence from the Swedish 5 min STEL value of 10 p.p.b. is to be expected in several plants.
The workers in continuous foaming plants were the highest exposed group in the study, but a striking difference in exposure was seen between the two plants studied. The mean 8 h TWA exposure levels in plant CF2 (4.1 p.p.b.) was the highest for all plants in the study, while the exposure in CF1 was a factor of 4 lower. The main reason for this difference was that in plant CF1 the foaming process was more enclosed than in plant CF2. In plant CF2, personal monitoring has previously been performed by Tinnerberg et al. (1997) using a paper tape method. In that study, the mean 8 h TWA exposure to TDI was also 4.1 p.p.b. (n = 12), but air sampling was not performed during the time when PPE was used, indicating that the exposure was considerably higher in that study. Other studies in continuous foaming plants have measured a mean 8 h TWA exposure to TDI of 5.7 p.p.b. for 29 workers using a paper tape method (Omae et al., 1992) and 5 p.p.b. for nine workers using filters impregnated with 2MP (Maitre et al., 1993).
The exposure levels of isocyanates in the flame lamination plants were 1.8 p.p.b. in FL1 and 1.0 p.p.b. in FL2. The lower exposure levels in FL2 compared with FL1 were probably due to the lower production intensity in plant FL2 on the day of monitoring. However, when comparing equivalent stationary samples collected during production in the two plants, similarities in air levels were observed. This indicates that the emissions of isocyanates during normal production in these plants are of the same order of magnitude. In plant FL1, personal monitoring has previously been performed and the reported mean 8 h TWA level of TDI was 1.1 p.p.b. as measured with filters impregnated with MAMA in that study (Lindh et al., 1997). In the flame laminating plants, personal exposure to PI was also monitored in the working atmosphere and this is, to our knowledge, the first time a 8 h TWA for PI exposure has been reported. However, comparisons with the DBA method showed that the 2MP method greatly underestimates the true exposure levels (Sennbro et al., 2004). Stationary monitoring performed in FL1 and FL2 using the FINMP and DBA methods revealed very high levels of ICA, compared with the Swedish OEL of 5 p.p.b. However, the Swedish general OEL is based on data on diisocyanates, whose critical effect is sensitization. Since no cases of sensitization caused by exposure to ICA have been reported, application of the general OEL and STEL to ICA is questionable. As shown in Fig. 1, the dominant isocyanate in air in the flame lamination plants is ICA. In the stationary samplings, the mean contribution of ICA to the air levels of monitored isocyanates was 75%. When recalculating the isocyanate levels as TRIG instead, as performed in other countries, the mean contribution of ICA was 65%. Adding this contribution of ICA to the monitored personal exposure to TDI in FL1 and FL2 indicates that the STEL as well as the OEL are exceeded in these plants. Airborne ICA due to thermal degradation of PUR in the work environment has previously been demonstrated by Karlsson et al. (2002) and Henriks-Eckerman et al. (2002).
For the seven moulding plants, the average 8 h TWA levels of isocyanates were 0.2–0.8 p.p.b. In the moulding plants using MDI or NDI (M1 and M2), the mean 8 h TWA exposure levels were of the same order of magnitude as in the moulding plants using TDI (M3–M7). In plants M5–M7 the manufacturing processes were almost identical, but the median personal exposure levels were 2–4 times higher in plant M7 compared with plants M5 and M6, probably due to insufficient ventilation. This was also confirmed by stationary monitoring. In previous studies in moulding plants, Omae et al. (1992) found a mean personal 8 h TWA exposure to TDI of 0.1 p.p.b. for 28 individuals, and Meredith et al. (2000) found mean 8 h TWAs of 1.8 and 1.2 p.p.b. in two different groups of TDI- and MDI-exposed workers in two companies. In both studies a paper tape sampling technique was used for personal sampling.
The workers in the plants performing low or no heating processes were the lowest exposed group, which was expected.
Other studies reporting 8 h TWA for isocyanates are from a TDI (Butcher et al., 1977) and a MDI production plant (Meredith et al., 2000). In the TDI plant, the median exposure was 5 p.p.b. and in the MDI plant, the exposure for 90% of the cases was <2 p.p.b. In both these studies, personal monitoring was performed by a paper tape technique.
In this study we have focused on measuring as many individuals as possible instead of studying the variation. To study fully the variation of exposure between the plants, working shifts and individuals, repeated measurements on the workers would be preferred. Still, we have tried to estimate the variation by calculating CV values based on a very low number of observations. Table 5 shows that the CV values vary between shifts in the same company and no clear tendency of the variation can be seen for the plants or types of handling that we have studied. There was no difference in exposure between shifts in plant M6 even though the p.m. shift had a lower production level but the same exposure level. In plant M4, where five different shifts were monitored (Table 5), the mean exposure varied by a factor of 3 between shifts that in principal were doing the same work. The conclusion is that there is a large variation within this plant as well as between plants that perform similar manufacturing processes, which is an important issue to be aware of when performing epidemiological studies based on group data. A possibly better way to estimate the variation in exposure is to use biomarkers of isocyanate exposure (Sennbro et al., 2003). This is not as time consuming as air monitoring, and urinary sampling may even be performed by the workers themselves.
We have shown that with the applied strategy, using two 2MP filters, the 8 h TWA isocyanate exposure could be measured for a large group of individuals and the personal exposures in different industrial processes have been compared. By additional stationary monitoring using three different methods, emission and area exposure levels were monitored, which confirmed personal monitoring and sometimes revealed unexpectedly high peak exposures. The results of the survey describe the differences in isocyanate exposure for different industrial processes and also for plants with the same processes. These findings led to several preventive actions in the monitored plants in order to decrease exposure.
Acknowledgements—The authors thank Birgitta Björk, Cecilia Gustavsson, Helene Ottosson, Åsa Amilon and Karin Paulsson who assisted in the air sampling. The authors also thank Arbetsmarknadens Försäkringsaktiebolag (AFA Foundation), Sweden and Forskningsrådet för Arbetsliv och Socialvetenskap (Swedish Council for Working Life and Social Research) for financial support of this work.
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* Author to whom correspondence should be addressed. E-mail: hakan.tinnerberg{at}ymed.lu.se
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Batlle R, Colmsjö A, Nilsson U. (2001) Development of a personal isocyanate sampler based on DBA derivatization on solid-phase microextraction fibers. Fresenius J Anal Chem; 371: 514–8.[Medline]
Baur X, Marek W, Ammon J, et al. (1994) Respiratory and other hazards of isocyanates. Int Arch Occup Environ Health; 66: 141–52.[CrossRef][Web of Science][Medline]
Butcher BT, Jones RN, O’Neil E, et al. (1977) Longitudinal study of workers employed in the manufacture of toluene-diisocyanate. Am Rev Respir Dis; 116: 411–21.[Medline]
Health and Safety Laboratory. (1999) Organic isocyanates in air, MDHS 25/3. Sudbury: HSE Books.
Henriks-Eckerman M-J, Välimää J, Rosenberg C. (2000) Determination of airborne methyl isocyanate as dibutylamine or 1-(2-methoxyphyl)piperazine derivatives by liquid and gas chromatography. Analyst; 125: 1949–54.[Medline]
Henriks-Eckerman M-J, Välimää J, Rosenberg C, Peltonen K, Engsröm K. (2002) Exposure to airborne isocyanates and other thermal degradation products at polyurethane-processing workplaces. J Environ Monit; 4: 717–21.[CrossRef][Web of Science][Medline]
Karlsson D, Spanne M, Dalene M, Skarping G. (1998) Determination of complex mixtures of airborne isocyanates and amines. Part 4. Determination of aliphatic isocyanates as dibutylamine derivatives using liquid chromatography and mass spectrometry. Analyst; 123: 117–23.[CrossRef]
Karlsson D, Spanne M, Dalene M, Skarping G. (2000) Airborne thermal degradation products of polyurethane coatings in car repair shops. J Environ Monit; 2: 462–9.[CrossRef][Web of Science][Medline]
Karlsson D, Dalene M, Skarping G, Marand Å. (2001) Determination of isocyanic acid in air. J Environ Monit; 3: 432–6.[Medline]
Karlsson D, Dahlin J, Skarping G, Dalene M. (2002) Determination of isocyanates, aminoisocyanates and amines in air formed during the thermal degradation of polyurethane. J Environ Monit; 4: 216–22.[CrossRef][Web of Science][Medline]
Levine SP, Hillig KJD, Dharmarajan V, Spence MW, Baker MD. (1995) Critical review of methods of sampling, analysis, and monitoring for TDI and MDI. Am Ind Hyg Assoc J; 56: 581–9.
Lindh P, Dalene M, Tinnerberg H, Skarping G. (1997) Biomarkers in hydrolysed urine, plasma, erythrocytes among workers exposed to thermal degradation products from toluene diisocyanate foam. Analyst; 122: 51–6.[CrossRef][Medline]
Maitre A, Berode M, Perdrix A, Romazini S, Savolainen H. (1993) Biological monitoring of occupational exposure to toluene diisocyanate. Int Arch Occup Environ Health; 65: 97–100.[CrossRef][Web of Science][Medline]
Meredith SK, Bugler J, Clark RL. (2000) Isocyanate exposure and occupational asthma: a case-referent study. Occup Environ Med; 57: 830–6.
Norén JO. (2000) Mätprojekt isocyanater, rapport 2000:9, arbetarskyddsstyrelsen (in Swedish). Available online at: http://www.av.se/publikationer/rapporter/2000_9.pdf.
Omae K, Higashi T, Nakadate T, Tsugane S, Nakaza M, Sakurai H. (1992) Four-year follow-up of effects of toluene diisocyanate exposure on the respiratory system in polyurethane foam manufacturing workers. Int Arch Occup Environ Health; 63: 565–9.[Medline]
Östin A, Sundgren M, Ekman J, Lindahl R, Levin J-O. (2002) Analysis of isocyanates with LC-MS/MS. In Lesage J, DeGraff ID, Danchik RS, editors, Isocyanates: sampling, analysis and health effects, American Society for Testing and Materials Special Technical Publication 1408. West Conshohocken, PA: American Society for Testing and Materials.
Sennbro CJ, Lindh CH, Tinnerberg H, et al. (2003) Development, validation and characterisation of an analytical method for quantification of hydrolysable urinary metabolites and plasma protein adducts of 2,4- and 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate and 4,4'-methylenediphenyl diisocyanate. Biomarkers; 8: 204–17.[Medline]
Sennbro CJ, Lindh CH, Ekman J, Welinder H, Jönsson BAG, Tinnerberg H. (2004) Determination of isocyanates in air using 1-(2-methoxyphenyl)piperazine impregnated filters; long-term sampling performance and field comparison with impingers with dibutylamine. Ann Occup Hyg; 48: 415–24.
Spanne M, Tinnerberg H, Dalene M, Skarping G. (1996) Determination of complex mixtures of airborne isocyanates and amines. Part 1. Liquid chromatography with ultraviolet detection of monomeric and polymeric isocyanates as their dibutylamine derivatives. Analyst; 121: 1095–99.[CrossRef]
Streicher RP, Reh CM, Key-Schwartz RJ, Schlecht PC, Cassinelli ME, O’Connor PF. (2000) Determination of airborne isocyanate exposure: considerations in method selection. Am Ind Hyg Assoc J; 61: 544–56.
Tinnerberg H, Dalene M, Skarping G. (1997) Air and biological monitoring of toluene diisocyanate (TDI) in a flexible foam plant. Am Ind Hyg Assoc J; 58: 229–35.[Medline]
Vandenplas O, Malo J-L, Saetta M, Mapp CE, Fabbri LM. (1993) Occupational asthma and extrinsic alveolitis due to isocyanates: current status and perspectives. Br J Ind Med; 50: 213–28.[Web of Science][Medline]
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