勞工噪音及化學物質暴露對聽覺功能之影響

The association of hearing loss and exposed to chemicals and noise

李姿諭(Tzu-Yu Lee)

指導教授 ： 吳聰能 ； 莊弘毅

高雄醫學大學/健康科學院/職業安全衛生研究所/碩士(2004年)

摘要

造成職業性聽力損失的原因目前熟知除了是噪音暴露所造成的之外，近年來已有相當多的研究發現暴露耳毒性化學物質相對的也會對聽覺造成損害。本研究主要目的是調查噪音作業環境中，使用苯、二甲苯及苯乙烯這種亦會影響人體聽力損失聽力的化學物質，對勞工聽力損失的影響及程度。
本研究從九十二年三月到九十二年十一月收集2家工廠共213位員工人參與本計畫；排除有中耳疾病、糖尿病、其他重大疾病之後，共176個人，所收集的資料包括；問卷收集(基本資料)、環境中苯、二甲苯、苯乙烯濃度及噪音暴露、個人尿液中苯的代謝物-trans, trans- muconic acid(t,t-MA)及S-phenylmercapturiz acid(S-PMA)、二甲苯的代謝物-o-, m-, p- methylhippuric acid(2,3,4-MHA)及苯乙烯代謝物-Mandelic acid(MA)及Hippuric acid(HA)還有個人聽力檢查四部份，將收集到的176個人分成化學物質合併噪音暴露組(第一組)、單純噪音暴露組(第二組)及都沒有暴露組(第三組)等三組。
研究結果發現，三組的平均聽力閾值其化學物質合併噪音暴露組及單純噪音暴露組的聽力閾值皆比都沒有暴露組高，且在右耳500 Hz、左耳500 Hz 、1000 Hz及 2000 Hz部分達統計上顯著差異。但並無法看出化學物質合併噪音所影響聽力的結果大於單純噪音暴露的結果。此外，在控制其他干擾因子經由回歸分析結果，年齡對聽力有顯著的影響，且越在高頻其影響幅度越大。
另外，探討左右耳與各頻率間關係發現不論是左右耳間之相關性，或是在500 Hz~6000 Hz頻率間與頻率間其相關係數很大(0.5~0.7)，特別是在相鄰的音頻區之間，因此考慮各頻區間的影響，利用Mixed-Model 及GEE Model來控制各頻區間的影響，探討化學物質暴露對聽覺系統之影響，結果發現造成聽力損失最大的頻率是在6 kHz，4 kHz次之。
從尿液中代謝物濃度以mixed model分析的結果發現，在二甲苯代謝物部分(2,3,4-HMA)每增加1mg/g creatinine 聽力閾值會相對提升，雖然提昇幅度不大，由此可知暴露在二甲苯環境下其聽力閾值會有所影響。
在環境中化學物質濃度部分與聽力閾值損失情形比較，皆無顯著差異，此部分可能是因為勞工暴露化學物質的濃度過低，因此無法看出彼此間之相關性，但從以25分貝為臨界值使用GEE Model來看，發現化學物質合併噪音暴露組其發生聽力損失危險性比都沒有暴露組高13倍，而此組工人暴露的噪音分貝值不大(低於85分貝)，可見在有耳毒性化學物質的工作環境中，縱使其暴露噪音量不大，還是會對聽力造成影響，因此在噪音防制部份，若有同時暴露耳毒性化學物質的工作場所，其可容許之噪音量應該更低，已達保護勞工之要。
研究限制：在此研究的限制是無法真正區分化學物質合併噪音暴露組或單純化學物質暴露組，因為所收集的這兩家化工廠的員工其平均工作年資在12年以上，而其員工的職位並非不變的，工廠內同部門的員工會定期調至不同的工作項目，而此研究分組是以現階段工作內容作為分類，其尿液中代謝物濃度只能表示其短期暴露情形，但聽力損失是屬於長期暴露的結果，所以並無法從此明顯看出暴露與結果的關係。
此研究之優點：與以往一般文獻中針對聽力損失與各因子之相關係的paper最大的不同是在於：已往文獻中對於outcome(聽力損失)的頻估只分成左右耳及各頻區分別探討，但本研究將左右耳間及各頻區間相互影響列入考慮，也看出其相關性，這是與以往文獻中最大的差異點。

關鍵字

聽力損失 ； 苯乙烯 ； 二甲苯 ； 苯

並列摘要

Some researchs reported that exposed to chemical led workers hearing impairment especially, the neurotoxic solvents. The aim of the this study was to investigate the effect of occupational exposure to benzene, xylene, styrene and noise on the auditory system. Originally, 213 workers were invited to participate in the study from March, 2003 to November, 2003. Excluding otitis media, diabete, and other systemic diseases, thus, a total of 176 subjects were included in the study, and divided into 3 groups: noise and chemicals group (group1), noise only group(group2) and non-exposure group(group3). Data were collected through a questionnaire on work history, occupational and nonoccupational noise exposures. The concentration of benzene, xylene, and styrene in the working environment, and pure-tone audiometry(PTA) were measured by standard methods. Total benzene exposure was assessed by the biological monitoring of trans, trans- muconic acid(t,t-MA) and S-phenylmercapturiz acid(S-PMA) in the urine. Total xylene exposure was assessed by the biological monitoring of o-, m-, p- methylhippuric acid(2,3,4-MHA) in the urine. Total styrene exposure was assessed by the biological monitoring of Mandelic acid(MA) and Hippuric acid(HA) in the urine. Urine samples were collected twice, pre-shift and post-shift.The means and standard deviations (SDs) of hearing threshold of the both noise and chemicals group and noise only group were higher than non-exposure group, especially the 500 Hz on right ear, and 500 Hz, 1k Hz as well as 2k Hz on left ear. We can’t find the difference between group 1(noise and chemicals both) and group 2 (noise only). The main effect of hearing impairment were age using multiple regression to adjust potential confounders, especially of high frequency. Because of the strong correlation of right and left ears, and among the different frequency, the mixed effect models and GEE methods were used. We found the frequency of hearing impairment were the most severe in the 6 k Hz frequency using Mixed models and GEE method with adjustment of potential confounders. The significant result of biological monitoring of urine using Mixed models, revealed that increase of 1 mg/g creatinine 2,3,4-MHA would increase hearing threshold. The chemicals air concentrations and hearing threshold were not significant in this study. The reason may be that workers exposure to low concentration of chemicals. GEE Model analysis revealed almost a 13-fold increase in the odds ratio of developing hearing loss related to noise and chemicals group, and in this group workers exposed to low dB noise(lower 85 dB).However we can’t discriminate noise and chemicals group and chemicals only group in this study. Because our study classified groups by job titles, but workers’ average working years were more then 12 years, during their tenure of work, they might change their job or working areas. In addition, workers in this study exposed to extremely low levels of benzene, xylene, and styrene. However workers exposed to autotoxicants with or without noise both need hearing protection program.

並列關鍵字

Benzene ； Xylene ； Styrene ； hearing loss

參考文獻

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