Annals of Occupational Hygiene Advance Access originally published online on June 17, 2005
Annals of Occupational Hygiene 2005 49(6):529-533; doi:10.1093/annhyg/mei025
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2005 British Occupational Hygiene Society Published by Oxford University Press
Original Article |
Should Styrene be Sampled on the Left or Right Shoulder?—An Important Question in Employee Self-Assessment
1 Department of Occupational and Environmental Medicine, University Hospital of Northern Sweden, SE-901 85 Umeå, Sweden; 2 The Department of Public Health and Clinical Medicine, Occupational Medicine, Umeå University, SE-901 87 Umeå, Sweden; 3 Department of Mathematical Statistics, Umeå University, SE 901 87 Umeå, Sweden
* Author to whom correspondence should be addressed. Tel: +46 90 785 25 52; fax: +46 90 785 24 56; e-mail: Kare.Eriksson{at}envmed.umu.se
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
A self-operated personal sampling technique called ‘self assessment of exposure’ (SAE) has been suggested as an easy method for collecting inhalation exposure data, as the workers themselves are performing the sampling. Employers and employees have raised the question of whether a different estimate of the air concentration is likely to be obtained depending on whether the sampler is fastened at the left or the right shoulder. In order to answer this question, the exposure to styrene vapour in two different small enterprises within the reinforced plastics industry was measured. Seven workers participated and the air sampling was performed by diffusive sampling. We observed no statistically significant difference in the determined air concentration of styrene between the left and right shoulder (P = 0.878). The results strongly indicate that the fastening of a sampler on the left or right shoulder does not produce a difference in the estimation of the inhalation exposure. SAE can thus be used to collect reliable exposure data of styrene vapour. The reliability of SAE will most certainly inspire occupational hygienists, physicians and other experts to involve the workers in repeated exposure measurements. Taking the exposure variability into account, repeated measurements are crucial when evaluating acute and chronic health effects following inhalation exposure to gases and vapours from chemical hazards.
Keywords: breathing zone • diffusive sampling • inhalation • occupational exposure monitoring • reinforced plastics industry • styrene
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
The number of exposure measurements of chemical hazards in the working environment has decreased during the last two decades in Sweden. A possible explanation is that the cost, including the fee for a specialist performing the assessment and the charge from the laboratory carrying out the analysis, is considered to be too high, especially for a small or medium sized enterprise. Furthermore, there is a belief that technical improvements have generally reduced the inhalation exposure, but unfortunately few measurements have been carried out to verify this assumption. The reduction in exposure measurements performed is a dilemma for epidemiologists, physicians and others studying health effects following long-and/or short-term exposure to different chemical substances, as knowledge of exposure levels is not present. A possible technique to increase the number of exposure measurements within companies or industrial branches might be to get the workers themselves involved in the process of collecting exposure data. For this purpose, recently, Liljelind et al. (2000
, 2001) have performed studies among tank truck drivers, sawmill workers and employees in the plastic reinforced industry. The workers assessed their exposure to benzene, monoterpenes and styrene with a diffusive sampler. Following an oral and written instruction, they handled three samplers at each sampling occasion. They opened the samplers, and fastened them in parallel on the left or the right shoulder, with the diffusive inlet of the sampler pointing upwards. Following sampling, the workers closed the samplers and sent them by mail back to the laboratory for analysis at the end of the workday, or the following morning. There was no statistically significantly difference in self-estimated exposure compared with results obtained by a trained occupational hygienist performing air sampling at the same work places at 8 out of 10 workplaces (Liljelind et al., 2001). During the self assessment of exposure (SAE) studies one question was frequently raised: does the positioning of the diffusive sampler, i.e. on the left or right shoulder, show a difference in the determined air concentration? This point may be crucial and needs to be answered to give support to the SAE method. We are only aware of one field study that has been published on the subject ‘breathing zone concentration variations of vapours’. Malek et al. (1999), investigated the exposure to styrene among spray gun operators and rolling and tucking operators by diffusive sampling. The sampler used was the 3M open faced monitor. A statistically significant difference in air concentration of styrene was detected at the nose in comparison with concentrations detected at the left lapel, right lapel and chest, representing 90, 84 and 76% of the concentration at the nose, respectively, following exposure during 55–90 min. The mean concentrations of left and right lapel were not statistically significantly different. The aim of this study was to investigate whether placing the tube sampler on the left or the right shoulder affects the estimated inhalation exposure of styrene vapours.
|
EXPERIMENTAL PROCEDURES |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Premises and work process
Two enterprises in the fibreglass reinforced plastics industry took part in the investigation. At one of the companies, bathroom sinks for hotels were produced. The work process consisted of the following tasks; the workers put tape at the inner sides and at the bottom of the mould so that the product could be easily removed, following hardening. Then the workers poured styrene into the mould. Following hardening, the individual used compressed air to remove the product from the mould. Finally, the product was ground and polished. The work cycle was completed within
2 h and then it was repeated. The premises had a general ventilation system and in addition local extractors were installed in the vicinity of the different workplaces to further reduce the exposure to styrene. Five workers participated in the study. Four of the workers rotated between different tasks such as taping of moulds, casting and removing of product from the mould. The fifth worker was a foreman. Sampling was performed during the morning shift or the afternoon shift for four of the workers (worker 2, 3, 4 and 5 in Tables 1 and 2). The foreman's exposure was assessed during the morning shift and the afternoon shift, including a lunch break of 30 min (worker 1 in Tables 1 and 2).
|
|
At the other industry, plastic boats and other products such as roofs to horse wagons were produced. The company is a small-sized enterprise employing three workers. Styrene formulation and glass fibre were sprayed onto the object with a hand held airless spray gun. The use rate during spraying was
0.6 kg of formulation and glass fibre min–1. This task was carried out with the object in a ventilated spray area and with the worker standing in the vicinity of the opening to the spray area. Following spraying, which was carried out for 2–3 min, the individual and a colleague used a hand held roller with a short or an extended handle to smooth out the mixture of styrene formulation and glass fibre over the surface of the sprayed area and to expel air pockets. Rolling was carried out within the spray area. The procedure of spraying and rolling was repeated several times depending on the product being produced. The exposure was assessed during the morning and afternoon shift for these two workers with a sampling time of 255 and 235 min, respectively (worker 6 and 7 in Tables 1 and 2). Sampling was performed during lunch break which lasted 45 min.
Air sampling and analysis
Sampling of styrene vapour was performed using a diffusive sampler [stainless tubes, 90 mm x 6.3 mm O.D. x 5.0 mm I.D (Perkin-Elmer tube®) containing 300 mg of Tenax TA, 60–80 mesh (Chrompack)]. The samplers were conditioned and handled, as described recently (Liljelind et al., 2001). The sampling rate for styrene has been estimated to be 0.463 ml min–1 (Wright, 1993). The workers were given oral and written information on how to handle the samplers. They were told to place two samplers on each shoulder and to wear them during the whole sampling process. The samplers were to be opened at the start of the sampling period and closed at the end of the sampling period. Two samplers were used in parallel, at the right and left shoulder of each worker, as we wanted to study the reliability of the monitor. The diffusive inlet of the tube was positioned upwards. After sampling, the samplers were returned to the laboratory by mail. At the laboratory the samplers were kept at room temperature until analysis, which was performed within 2 days after sampling. The analysis of styrene was performed by thermal desorption and gas chromatography. The gas chromatographic separation was carried out on a Perkin Elmer gas chromatograph with a fused silica column (HP Ultra 25.0 m x 0.22 mm I.D., coated with a cross-linked 5% phenylmethylsilicone, film thickness 0.33 µm) and a flame ionisation detector operated at 270°C. Helium was used as carrier gas and the pressure on the injector and the column was 30 psi (Liljelind et al., 2001).
The workers received the results within a week following analysis.
Statistical analysis
The agreement between two parallel samplers fastened on the same shoulder was calculated by using the ratio between the estimated air concentrations of styrene by each sampler. The inhalation exposure assessment based on whether the samplers were fastened on the left or right shoulder was calculated using all the data shown in Table 1.
Given the design of the study the data were analysed using an ANOVA model (Proc GLM in SAS 9.1, SAS, Inc., Cary, NC, USA) which could be written as
 |
Yijkl is the measurement on the kth side of worker i in shift j, µ is the total grand mean, i.e. the mean of all measurements, 
i is the effect of worker i, ßj is the effect of shift j, 
k is the effect of shift k and 
l(jk) is the effect of the duplicate measurements within side k in shift j. The crossed terms, ik and ßjk, describe the interaction between the workers and left or right shoulder and with shift and left or right shoulder, respectively. 
ijkl is the residual error term. It is assumed that the residuals can be seen as a random sample from an N(0, 
2) distribution. For calculating the mean squares and the F-values, type-III sums of squares were used as we wanted to test the individual effects independent of the other parameters in the model. A P-value <0.05 was considered statistically significant.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
The mean ratio between the air concentrations of the two parallel diffusive samplers on the same shoulder was 1.03, indicating that it is not necessary to use more than one sampler. However, a relatively high difference in the estimated concentration was detected between the parallel samplers for individual No. 3 which showed a ratio of 0.69 on the left shoulder and 2.08 on the right shoulder, respectively (Table 1). The observed difference between the two samplers may have been caused by a chemical analytical error. During thermal desorption–gas chromatography, the entire sample is analysed and it was thus not possible to perform an additional analysis of the sample in question to verify the result of the chromatographic analysis. Another explanation might be that the diffusive opening of one of the samplers may have been covered by a crease of the worker's clothing causing a reduction in the diffusive rate of styrene into the sampler. In addition, droplets or an aerosol of styrene may have been deposited at the vicinity of the opening of one of the samplers during one or more tasks performed. Vapour from the deposited styrene may have contributed to the higher amount of styrene in one of the samplers. The exposure of styrene at left and right shoulder for the participating individuals ranged between 6.0–88.5 and 6.0–83 mg m–3 with a mean (AM) of 28 and 28 mg m–3, respectively (Table 2).
We observed no statistically significant difference in the determined air concentration of styrene between the left and the right shoulder P = 0.878 (Table 3). No significant interaction between the different effects (i and k) could be detected. If a significant interaction had been detected, the effect from the left or right shoulder would have been difficult to interpret. No significant effect could be detected from the duplicate samplers (l) indicating that they operate correctly. We do note a significant effect from workers and shifts, P < 0.001 and P = 0.027, respectively (Table 3), indicating differences between the workers and the shifts, which was expected as sampling was performed at two different enterprises. The residual plot showed that the residuals were randomly centred around the zero mean, i.e. no signs of heteroscedacity (data not shown) and the normality assumption for the residuals could not thus be rejected (P = 0.198, Shapiro–Wilk test) indicating that the model represents the data well. A paired t-test would possibly be adequate to test the question raised but it seems unlikely that the difference (if present) would be systematic in direction, i.e. from left to right or vice versa, so we chose the more complex ANOVA model for the analysis. We realize that the power of detecting differences in a relatively small dataset is low. Interestingly our results are in accordance with the results in the investigation performed by Malek et al. (1999), where no statistically significant difference in estimated air concentration of styrene at left and right lapel could be detected. However, they showed the existence of a breathing zone concentration variation of styrene during spraying and rolling and tucking, with concentrations detected at the left lapel, right lapel, and at the chest representing 90, 84 and 76% of the concentration at the nose. Styrene aerosol was emitted during spraying and drops and splashes, most likely during rolling and tucking. Aerosol and liquid drops of styrene most certainly deposited onto the face of the 3M diffusive sampler during these tasks and the vaporized styrene from the face of the sampler was collected by the sorbent. Malek does not discuss this in his paper, but in our opinion deposition of styrene onto the face of the diffusive sampler may have contributed to a relatively large extent to their observation. Our opinion is supported by Dobos (2000). He compared diffusive sampling (3M 3500 Organic Vapour Monitor) and pumped sampling (charcoal tubes) of styrene in fibreglass boat manufacturing plants. Side-by-side samples on the same lapel were attempted. Dobos found that the diffusive samplers estimated an air concentration of styrene, which was 31% higher than the concentration measured with the charcoal tubes. The author stated that the difference in the estimated air concentrations was explained by the deposition of styrene onto the face of the diffusive monitor. The aerosol deposition hypothesis is further supported by Van den Hoed (1987), who reported that 3M 3500 Organic Vapour Monitors and pumped sampling using charcoal tubes were found to yield identical average results in personal air monitoring for styrene when aerosols were not present. He also stated that if aerosols were present, large differences in estimated air concentration could be expected between diffusive sampling and pumped charcoal tube sampling. Thus, open face diffusive samplers seem to be sensitive to aerosol deposition. If the tube sampler used in this study shows a comparable sensitivity to styrene aerosol, it needs to be further studied but our results do not point in that direction.
|
Liljelind et al. (2000
, 2001) have suggested that SAE is a useful and low-priced device to collect reliable exposure data. This study strengthens the arguments for SAE by demonstrating that no statistically significant difference of the determined air concentration of styrene vapour was found when the sampler was fastened at the left or right shoulder. In addition, the performance of the diffusive sampler is reliable and there is no need to use more than one sampler. Thus, our result raises the question of workers performing air sampling using a diffusive sampler to collect reliable data, i.e. to replace industrial hygienists or other sampling experts during different applications. Collecting inhalation exposure data is a relatively complex procedure, including, for instance, selection of a suitable adsorbent, estimation of the length of sampling time and knowledge on how to handle the samplers. However, when an expert makes a final decision on this subject, we believe that the worker can perform air sampling on a routine basis following oral and written instructions. This instruction should include detailed information on how to open and close the diffusive sampler, how to fasten it onto the worker and at which position, how to handle the sampler following sampling and other information considered crucial. In addition, sampling should be supplemented by a worker's diary in which information about work task, length of task, and other determinants of exposure are written down. One problem that might arise if SAE is used in work places is that the employer may conceal the results. We do not have a solution to this problem, but our experience indicates that this is not really a problem among Swedish employers in general. If the worker is well informed about the sampling process, we believe that he or she may collect reliable data in research projects as well, though supervised by an industrial hygienist. The presence of an industrial hygienist during research projects will most certainly minimize the problem of results being concealed. The simplicity of SAE also makes it easy to perform repeated assessments at a relatively low cost, which gives a good overview of the worker's mean exposure during different work shifts; it also provides information about the variability of the exposure between workers and for individual workers within a production unit and within the industrial branch. Knowledge of the variability in exposure is useful when studying acute as well as chronic health effects following exposure to styrene vapour. We have studied exposure to styrene, but we strongly believe that the results of this study are applicable in other working situations where there is an exposure to vapours or gases from other chemical hazards.
|
ACKNOWLEDGEMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
University Hospital of Northern Sweden and Umeå University financially supported this study which is gratefully acknowledged.
Received March 15, 2005; in final form May 8, 2005
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
|---|
Dobos RT. (2000) Field investigation comparing diffusion badge and charcoal tube monitoring for styrene. Appl Occup Environ Hyg; 15: 673–76.[Medline]
Liljelind IE, Strömbäck AE. Järvholm BG et al. (2000) Self-assessment of exposure: a pilot study of assessment of exposure to benzene in tank truck drivers. Appl Occup Environ Hyg; 15: 195–202.[CrossRef][Medline]
Liljelind IE, Rappaport SM, Järvholm BG et al. (2001) Comparison of self- and expert assessment of occupational exposure to chemicals. Scand J Work Environ Health; 27: 311–17.[Web of Science][Medline]
Malek RF, Daisy JM, Cohen BS. (1999) Breathing zone concentration variations in the reinforced plastic industry; field measurements in a boat manufacturing plant. Appl Occup Environ Hyg; 14: 777–84.[Medline]
Van der Hoed N, van Asselen OLJ, van Dongen JPCM. (1987) Replicate side-by-side field comparison of 3M diffusive samplers versus charcoal tube samplers for styrene. Am Ind Hyg Assoc J; 48: 252–56.
Wright MD. (1993) Diffusive uptake rates for the Perkin-Elmer tube—BCR air sampling intercomparisons at Vito. HSE Report Ref. IR/L/IA/93/3 (Mol: Belgium).
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  T. Meijster, E. Tielemans, J. Schinkel, and D. Heederik Evaluation of Peak Exposures in the Dutch Flour Processing Industry: Implications for Intervention Strategies Ann. Hyg., October 1, 2008; 52(7): 587 - 596. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. HERTSENBERG, D. BROUWER, M. LURVINK, C. RUBINGH, E. RIJNDERS, and E. TIELEMANS Quantitative Self-Assessment of Exposure to Solvents Among Shoe Repair Men Ann. Hyg., January 1, 2007; 51(1): 45 - 51. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||