| Summary: | 博士 === 國立臺灣大學 === 環境衛生研究所 === 99 === Glycol ethers are widely used in industrial and household applications because of their chemical and physical properties. During the manufacturing process of bicycles, the dilute aqueous solution of 2-butoxyethanol (2-BE) is used to transfer decals to the frames. Workers usually transfer the decals by hand without using protective gloves. The concentration of dilute aqueous solution of 2-BE is about 10% (vol/vol), and the temperature is kept at around 25-30℃. Such work pattern will increase the exposure risk of 2-BE. Various animal studies using different routes of exposure (oral, inhalation, and dermal) have shown 2-BE to cause decreases in red blood cell counts and hemoglobin concentration, as well as red blood cell hemolysis, hemolytic anemia, and red blood cell osmotic fragility.
The objectives of this study were to evaluate the 2-BE exposure and hydrolyzed 2-butoxyacetic acid of the 2-BE transfer workers, 2-BE effect on oxidative stress and visual function, and to test the effects of the CYP2E1 genetic polymorphism on metabolism of 2-BE.
In the current study, 80 workers (including 31 2-BE transfer workers, 25 self-adhesive decals workers, and 24 assembly workers) were comprised at two bicycle manufacturing factories. Sociodemographics, work history, lifestyle factors, medical history, and subjective symptom were investigated by questionnaires. Subject 2-BE in personal air, pre- and post-work urines were sampled on the first (W1) and the fifth (W5) workday after a holiday. These samples were analyzed by gas chromatograph/flame ionization detector (2-BE in air) and gas chromatography/mass spectrometry (hydrolyzed 2-butoxyacetic acid, total BAA). Further, Subject blood was drawn from a vein for hemoglobin, oxidative stress, and polymorphism analysis. Color vision and contrast sensitivity were also conducted to evaluate the visual function of the subjects.
Of the 31 2-BE transfer subjects, mean 2-BE air level was 1.89 (W1) and 1.57 ppm (W5), and average postshift urinary total BAA was 446.8 (W1) and 619.4 mg/g creatinine (W5). Correlation of 2-BE air levels and postshift urinary BAA levels on these two workdays was poor. Although 2-BE air level was around 8.5% of the current TLV–TWA, the postshift BAA in urine of W1 and W5 was 123% and 210% more than the value of BEI, respectively. No hematopoietic effect was found for the study subjects.We speculated that the main reason for 2-BE absorption of them could be ascribed to the direct dermal contact. The evidence of accumulation also appeared in current research with the exposures of low-level 2-BE. Therefore, for the biological monitoring, it is highly recommended that the urine sample should be collected at the end of the workweek.
Many researches have already examined the effects of organic solvents on visual function. The color confusion index and visual contrast sensitivity test are some of the techniques purported to be a sensitive indicator. However, there was no significant difference between 2-BE transfer workers and assembly workers on these two indices. No visual dysfunction was found in the study subjects performed their tasks with hands direct contact to dilute aqueous solution of 2-BE (10%).
Of the oxidative stress, such as 8-OhdG and myeloperoxidase, there was also no significant difference between 2-BE transfer workers and assembly workers. Most of the subjects did not have alcoholic drinking and smoking habits. It seemed that exposure to low-level 2-BE did not cause significant difference of oxidative stress.
Previous study has reported a possible connection between mutant CYP2E1 genotype and low urinary excretion of free BAA in exposure to 2-BE. Our results showed that, after adjustment for 2-BE concentrations in personal air, neither Rsa I site polymorphism nor Dra I site polymorphism was significantly associated with the urinary BAA. This indicates that the CYP2E1 polymorphism may not be a modifying factor of 2-BE metabolism to modulate the excretion of urinary total BAA in our study population. Since 2-BE exposure from dermal route, alcohol dehydrogenase 2 and aldehyde dehydrogenase 2 were not evaluated in our study, the influence of the genetic polymorphism for CYP2E1 deserves further investigation for the interpretation of urinary BAA measurements.
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