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Iranian Journal of Environmental Health Science & Engineering, 2008, Vol. 5, No. 1, pp. 65-72 EXPOSURE TO ETHYLENE GLYCOL MONOBUTYL ETHER AND RELATED WORKERS HABITS IN AN INK FACTORY 1 W. C. Lin, 2 H. Y. Chang, *3 F. H. Chang 1 Department of Cosmetic Science, Chia Nan University of Pharmacy and Science, Tainan 717, Taiwan (R.O.C.) Received 10 October 2007; revised 25 November 2007; accepted 28 December 2007 Code Number: se08009 ABSTRACT Forty six workers from an ink factory were included in this study, in which, passive badge sampler and questionnaire interview were used to assess the concentrations of airborne exposure to ethylene glycol monobutyl ether during work shifts and to understand the subjects’ working habits. The geometric mean value (95% confidence interval) of the airborne ethylene glycol monobutyl ether concentrations was 0.12(0.08–0.19)ppm, with a range of <0.02–1.82ppm. The exposure group was exposed to statistically significantly higher ethylene glycol monobutyl ether concentrations than the control group (geometric mean value: 0.14vs. 0.03ppm; P=0.017). Some chromatograms showed that subjects were co-exposed to m-xylene, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether acetate. According to the completed questionnaires, subjects might also be exposed to 1,2,4,5-tetramethylbenzene, propylene glycol ethers, ethanol, 1,2,4-trimethylbenzene, methanol and diisononyl phthalate. This study also suggests that, the Taiwan occupational time-weighted average level of ethylene glycol monobutyl etherbe reconsidered with a view to being lowered. Key words: Occupational exposure, ethylene glycol monobutyl ether, passive badge, time-weighted average INTRODUCTION Ethylene glycol monobutyl ether (EGBE), one of the ethylene glycol ethers (EGEs), is often used as a solvent in surface coatings such as spray lacquers, quick-dry lacquers, enamels, varnishes, varnish removers, latex paint and printing inks; is also used as a cleaning fluid owing to its miscibility with both water and a large number of organic solvents (NIOSH, 1990). Unlike ethylene glycol monomethyl ether (EGME) and ethylene glycol monoethyl ether (EGEE), another two of the EGEs, EGBE has not been shown to be reprotoxic; rather, its main toxicological effect is hemolytic anemia (Lanigan, 1999; NTP, 1989). This lower toxicity has resulted in EGBE being the most widely used of all EGEs worldwide. However, in addition to the well-known development of hemolytic anemia resulting from EGBE exposure (both animal experiments and human studies), further harmful effects have been assessed and reported in recent years (Hughes, et al., 2001). The studies mentioned above are mainly based on animal experiments and the ingestion/inhalation of high doses of EGBE. Few occupational studies have discussed the exposure scenarios and relevant health effects upon workers chronically exposed to low levels of EGBE. Long-term exposure studies of rats and mice have reported both hemolytic and carcinogenic effects, raising concern that EGBE might be a human carcinogen (Gift, 2005); unfortunately, the effects of long-term occupational exposure to EGBE in humans have not been well-studied. The Occupational Safety and Health Administration (OSHA), American Conference of Governmental Industrial Hygienists (ACGIH), and the National Institute of Occupational Safety and Health (NIOSH) have set their respective airborne EGBE time weight averages (TWA) at 50, 20 and 5 ppm, respectively (OSHA, 2007), while in Taiwan, the Council of Labor Affairs (CLA) has a set TWA of 25ppm (CLA, 2003). The automation of manufacturing processes and improvements in the protective equipment being used have lowered the extent of exposure to workers. However, inhalation is not the only exposure route of EGBE for workers, and possible effects when workers are chronically exposed to low levels of EGBE need to be clarified. This paper assesses the EGBE exposure of workers in an ink factory by personal passive air sampling, evaluates subjects' working habits, and discusses the necessity of lowering the TWA value for EGBE. MATERIALS AND METHODS Study factory and subjects The ink factory investigated in this study specializes in the manufacture and sale of photoimageable solder and etching resist inks used in the production of rigid printed circuit boards. The raw materials used in the manufacture of the inks include pigments, solvents, resins (or binders) and other additives. The fluid component of the ink, made of binders (oils and resins) and solvents, called the vehicle, is the major source of volatile organic compound emissions. Batch process production of ink involves four major steps: preassembly and premix, pigment grinding/milling, product finishing/blending, and product filling/packaging. The workers in charge of the preassembly and premix processes (Group A) and those in charge of the pigment grinding/milling processes (Group B), both groups in the Department of Production, are considered as being exposed to EGBE more seriously than do those in charge of product finishing/blending and filling/packaging (Group C) in the Department of Production and the management staff (Group D). Group C has a lower exposure to EGBE because these employees work in a clean room with excellent ventilation control and process automation. Forty-one workers from Groups A and B formed the exposure group, while five workers from Groups C and D were the control group. All subjects were recruited voluntarily and when the sampling day proved convenient for them. Sampling and analysis of airborne EGBE Personal monitoring was performed using passive badges during February 2005 (phase I) and July 2006 (phase II). Measurements were performed on twenty-two and twenty-four voluntary workers in the first and second phases, respectively. The concentration of EGBE vapor in the breathing zone of individual workers (Groups AD) was measured by a diffusible sampling method, using a 3M personal passive badge (3M Co., Model 3500, St. Paul, USA). This study referred to the laboratory method (MDHS 88) of the Health and Safety Executive (HSE, 1997) and to a previous study (Sakai, et al., 1993) that have used passive badges to collect samples for the determination of levels of glycol ethers. In brief, the passive badge was attached to the worker's collar during the work shift. The diffusive uptake rate for the 3M 3500 sampler is 28.2mL/min (HSE, 1997). When the sampling was completed, the badge was sealed tightly with a plastic cap, temporarily stored in an ice-can, and then delivered back to the laboratory and kept at 4°C in a refrigerator until analysis. The materials collected by the passive samplers were desorbed in 1.5mL carbon disulfide (99.7%, Merck, Darmstadt, Germany). After shaking vigorously by hand and standing for 2 hours, the desorbed EGBE was analyzed by injecting the extract into a Varian 3800 gas chromatographer equipped with a flame ionization detector (GC-FID) and a Varian CP-8400 autosampler (Walnut Creek, CA, USA). A HP-5 capillary column (30mx0.32mm, 0.5ìm film in thickness, Agilent Technologies, USA) was used for the separation of each relevant compound. Injector and detector temperatures were set at 220°C; the column temperature was programmed to be 40°C for the initial 2 minutes, then increased from 40°C to 120°C at 10°C/min, and finally increased to 220°C at 15°C/min. The standard solutions of EGME, EGBE, ethylene glycol monoethyl ether acetate (EGEEA) and xylenes used were reagent grade, and were obtained from Merck Co. (Merck, Darmstadt, Germany). Quality control A quality assurance protocol for the sampling and analysis of airborne EGBE was implemented prior to the field study. The correlation coefficients (r) of the five-point calibration curves for EGBE were above 0.995. The desorption efficiency (DE) of EGBE was determined by spiking 90-µg liquid EGBE into the unused blank 3M 3500 samplers, sealing and leaving for at least 16 hours, then finally calculating the weight recovered divided by the weight applied; the DE in this study was found to be 132±3.8% (mean ± standard deviation). All the EGBE concentrations in the field studies were adjusted for their corresponding recoveries. The detection limit of EGBE was 0.02 ppm. During the period of real sample analysis, calibration checks and blank sample analysis were performed to ensure the analytical quality. Questionnaire interview Forty-six questionnaires in total were completed voluntarily by the workers in order to collect information on demographics, personal and working habits (smoking, alcohol drinking, personal protection equipment usage, etc.), and occupational history (department worked in, length of service, types of solvents used, etc.). Data treatment and analysis Data were calculated and analyzed, using EXCEL (Microsoft EXCEL 2003, Redmond, WA, USA) and SPSS software (Version 10.0; SPSS, Chicago, IL, USA). Concentrations below the detection limit (DL) were set to DL/2 for further data treatment. Student's t-test and one-way analysis of variance (ANOVA) were used to test the hypotheses that there were no differences in age, length of service or respiratory EGBE levels between or among the study groups, followed by Scheffe (equal variance) or Dunnett's T3 (unequal variance) Post Hoc tests if necessary. The normality of the data was evaluated using the Shapiro-Wilk test, due to the sample size being less than 50. Raw data not fitting the normal distribution were transformed to log base 10 values before ANOVA. The chi-square test was used to compare the working habits among the study groups. A value of P<0.05 (two-tailed) was considered statistically significant when testing the hypotheses. Descriptive statistics including arithmetic mean (AM), standard deviation (SD), geometric mean (GM) and its 95% confidence interval (95%CI), range and percentiles were calculated to present the airborne EGBE concentrations. RESULTS Analysis of basic personal information and working habits Seventeen of the 22 voluntary workers studied in the first phase (February 2005) were also included in the total of 24 voluntary workers studied in the second phase (July 2006). Therefore, when analyzing the data from the questionnaires, information from the same phase (i.e., 2005 or 2006) was first collected together and compared. The results of a comparison of phase I with phase II showed that, there was no significant difference in age, length of service or working habits (use of mask, gloves and protective clothing) (P=0.479, 0.517, 0.599, 0.260 and 0.694, respectively; data not shown here). Table 1 shows the details of the 22 voluntary workers in the first phase, divided into Group A (n=9), Group B (n=11) and Group C (n=2). All were male, and their average age was 32.8 (±5.4) years, with an average length of service of 5.8 (±1.9) years. While, there was no significant difference in age or length of service between the groups (P=0.596 and 0.720, respectively), there was a significant difference (all P<0.05) in the use of mask, gloves and protective clothing. Group A workers, who wore masks, gloves and protective clothing for more than 50% of their working hours, had the best protection of all the three groups. Workers in Groups B and C wore protective clothing for less than 50% of their working hours. The results for the 24 workers in the second phase are shown in Table 2. There were 9 workers in Group A, 12 in Group B and 3 in Group D; all were male, and their average age was 33.8 (±5.8) years, with an average length of service of 6.9 (±2.3) years. There was no significant difference in age, length of service or the use of mask or gloves between the groups (P=0.880, 0.405, 0.421 and 0.259, respectively); however, there was a significant difference (P<0.05) in the use of protective clothing. Similar to the results of phase I, the workers in Group A used protective clothing for more than 50% of their working hours, while workers in Groups B and C used protective clothing for less than 50% of their working hours. Respiratory EGBE exposure concentrations of workers Fig. 1 shows the airborne EGBE concentrations of Groups AD. Though the EGBE exposure concentrations of workers show differences between the groups, these differences were not statistically significant (P=0.090; Group A (AM; 0.38 ppm)>Group B (0.29ppm)>Group C (0.07ppm)>Group D (below DL: 0.02ppm)). When the data were further analyzed by comparing the exposure group (Groups A and B) and control group (Groups C and D), the results show that the exposure group (AM=0.33ppm) has a higher level of exposure than the control group (AM=0.03ppm), and this difference is statistically significant (P=0.017) (Fig. 2). If the workers are not considered by job category, the EGBC concentrations in the air were neither normal nor log-normal distributions in phases I, II and I+II (Table 3). In addition, the data show AM>median>GM (phase I: 0.38>0.16>0.09ppm; phase II: 0.22>0.17>0.10ppm), which indicates that the distribution of the concentration values is right-skewed. The concentrations of EGBE ([EGBE]) in the two phases were then compared: when using log10 (EGBE) to perform Student's t-test, no difference was found between the two phases (P=0.994). Therefore, the data from the two phases can be combined to calculate the EGBE concentration in the ink factory. The results showed the following: AM(SD)=0.30 (0.44)ppm> median=0.17ppm>GM(95%CI)=0.12(0.080.19)ppm; maximum concentration=1.82ppm. Comparison between data from the literature relating to occupational EGBE exposure Fig. 3 shows the reference values for airborne EGBE concentration obtained from the literature relating to occupational EGBE exposure and from this study. In a comparison with the results of other studies performed in the last decade, this study recorded lower levels (median: 0.17 ppm; GM: 0.12ppm; AM:0.30ppm) than the study by Haufroid et al., of 31 workers in a beverage package production plant (AM ± SD = 0.59 ± 0.27 ppm) and than the study by Yang (2002) of 20 workers in a printing circuit board company (the exposure concentrations in the morning-shift workers in the printing and developing areas were: AM±SD=1.52±1.18 and 0.37±0.30ppm, respectively). Since 1985, airborne EGBE concentrations in occupational environments have seldom been reported to be higher than the recommended exposure limit of 5 ppm issued by NIOSH (Angerer, et al., 1990; Haufroid, et al., 1997; OSHA, 2007; Sakai, et al., 1993; Söhnlein, et al., 1993; Veulemans, et al., 1987; Vincent, et al., 1993; Winder and Turner, 1992; Yang, 2002), the only exceptions being in the results of four studies reported around 20 years ago (Baker, et al., 1985; Denkhaus, et al., 1986; Kullman, 1987; Salisburg and Bennett, 1987). It is apparent that, the levels of occupational exposure to airborne EGBE have decreased in the past 20 years. Solvents co-exposed with EGBE in the ink factory The kinds of solvents mainly used in the ink factory were investigated by questionnaire, the results of which are shown in Table 4. From the responses of the workers to the questionnaires, 1,2,4,5-tetramethylbenzene (TeMB), EGEs, propylene glycol ethers (PGEs), ethanol (EtOH) and 1,2,4-trimethylbenzene (TMB) were found to be the top five solvents most frequently said to be used during ink processing, accounting for approximately 92% of the total number of solvents mentioned in the responses. TeMB was the most frequently-mentioned solvent, with the percentage of cases being approximately 67% (26/39), followed by EGEs, PGEs, EtOH and TMB at 62% (24/39), 62% (24/39), 26% (10/39) and 21% (8/39), respectively. These results suggest that workers are not only exposed to EGBE, but also to all of the solvents listed above. This has been proven by analysis of the samples by chromatogram (Fig. 4). DISCUSSION In this study, it was found that, the exposure of workers in this ink factory to EGBE was at a low level. A total of 32.6% of the 46 workers were exposed to levels below the detection limit (0.02ppm; Table 3). Analysis of the exposure concentrations showed that the distribution is right-skewed, which indicates that the median or GM is a better way to represent the results than the AM. In addition, to avoid overestimating the exposure concentration and including any statistical bias, values below detection limit were not processed as missing values. The EGBE exposure measurements of all the workers in the exposure group in this study were lower than the TWA values of OSHA, ACGIH and NIOSH (OSHA, 2007), and were also much lower than the TWA value suggested by the CLA of Taiwan25ppm (CLA, 2003). This study proposes that the TWA value for EGBE suggested by the CLA of Taiwan needs to be reduced to a lower level, according to the results of our study and the recommendation of NIOSH. In addition to accounting for human variability as recommended by NIOSH, our suggestion is based on the considerations listed below: 1. An improvement in management and workers' working habits in the factory can reduce exposure to EGBE. The study by Yang (2002) pointed out that the concentration of 2-butoxyacetic acid (metabolite of EGBE) in the urine of workers is associated with the EGBE concentration in the atmosphere (P<0.001), the length of service (P=0.007), and the habit of wearing gloves (P=0.039). Both the study by Yang (2002) and this study (Table 1 and 2) demonstrate that more than 50% of workers wore gloves during their working hours; this indicates that controlling the escape of evaporating solvents and encouraging the good habit of wearing gloves will help to reduce the exposure of workers to EGBE. 2. Use of lower toxicity solvents can reduce exposure to EGBE. In the results of the questionnaire, shown in Table 4, 62% of the workers mentioned using PGEs in their work, which was the same percentage as used EGEs (62%). These results indicate that this factory widely uses PGEs, which have a lower toxicity than EGEs. If the use of PGEs to replace EGEs can be increased, the workers' level of exposure to EGEs could be further reduced. The decreasing trend in the airborne EGBE concentration, as indicated by the reports of different researchers over the last two decades (Fig. 3), seems to coincide with points 1 and 2 of our considerations. 3. Low-level EGBE exposure can still damage health. Many studies of the past decade have suggested that, there is a correlation between air EGBE exposure and the levels of EGBE metabolite 2-butoxyacetic acid, and that EGBE exposure has a blood toxicity effect in humans. There is also evidence to suggest that EGBE may be carcinogenic, though the relevant studies used animal models in which the animals were exposed to high EGBE doses, or acute cases of human exposure to high EGBE concentrations (Gift, 2005). The current study demonstrates a case of workers' chronic exposure to low concentrations of EGBE in an ink factory, although we did not study whether or not exposure affects the 2-butoxyacetic acid concentration in the urine. However, the studies by Haufroid et al., (1997) and Yang (2002) demonstrated that there was a significant correlation between low EGBE exposure from the air to workers and the 2-butoxyacetic acid concentration in the urine after work (Haufroid, et al., (1997): r=0.55, P=0.0012; Yang: r=0.74, no p value described). In addition, Haufroid et al., (1997) pointed out that the hematocrit levels of the exposed workers were lower (3.3%, P=0.03) than those of the workers in the control group, and their mean corpuscular hemoglobin concentration was higher (2.1%, P=0.02) than that of the control group. Yang (2002) also showed that the mean corpuscular hemoglobin concentration in the exposed workers was significantly higher (P=0.04) than that of the workers in the control group. The results from these studies reveal that even exposure to low EGBE concentrations could affect the health of workers. Although the level of EGBE exposure from the atmosphere might be low, our study reveals that the workers are also exposed to several other volatile organic solvents (Table 4 and Fig. 4) during their working hours. Therefore, further study of the effects of co-exposure to these solvents on health might be necessary. ACKNOWLEDGEMENTS The financial support (Grants NSC93-2320-B-470-001 and NSC94-2314-B-470-001) of the National Science Council (NSC) of the Republic of China (R.O.C.) is gratefully acknowledged. We also thank Dr. Tzu-Chieh Chou of the Institute of Environmental Health, China Medical University, Taiwan for his invaluable suggestions and assistance in collecting the samples. REFERENCES
© 2008 Tehran University of Medical Sciences Publications The following images related to this document are available:Photo images[se08009t1.jpg] [se08009f2.jpg] [se08009t3.jpg] [se08009f4.jpg] [se08009f1.jpg] [se08009f3.jpg] [se08009t2.jpg] [se08009t4.jpg] |
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