Research | Environmental Medicine Hearing Loss in Workers Exposed to Toluene and Noise Shu-Ju Chang,1,2 Chiou-Jong Chen,3,4 Chih-Hui Lien,5 and Fung-Chang Sung 4,5,6 1Department of Industrial Management, Aletheia University, Taipei, Taiwan; 2Department of Environmental Engineering, National Ilan University, Ilan, Taiwan; 3Institute of Occupational Safety and Health, Council of Labor Affairs, Executive Yuan, Taipei, Taiwan; 4Institutes of Environmental Health, National Taiwan University College of Public Health, Taipei, Taiwan; 5Institute of Environmental Health, China Medical University College of Public Health, Taichung, Taiwan; 6Institutes of Preventive Medicine, National Taiwan University College of Public Health, Taipei, Taiwan In this study we investigated the risk of hearing loss among workers exposed to both toluene and noise. We recruited 58 workers at an adhesive materials manufacturing plant who were exposured to both toluene and noise [78.6–87.1 A-weighted decibels; dB(A)], 58 workers exposed to noise only [83.5–90.1 dB(A)], and 58 administrative clerks [67.9–72.6 dB(A)] at the same company. We interviewed participants to obtain sociodemographic and employment information and per- formed physical examinations, including pure-tone audiometry tests between 0.5 and 6 kHz. A contracted laboratory certified by the Council of Labor in Taiwan conducted on-site toluene and noise exposure measurements. The prevalence of hearing loss of ≥ 25 dB in the toluene plus noise group (86.2%) was much greater than that in the noise-only group (44.8%) and the administrative clerks (5.0%) (p < 0.001). The prevalence rates were 67.2, 32.8, and 8.3% (p < 0.001), respectively, when 0.5 kHz was excluded from the estimation. Multivariate logistic regression analysis showed that the toluene plus noise group had an estimated risk for hearing loss ≥ 25 dB, 10.9 times higher than that of the noise–only group. The risk ratio dropped to 5.8 when 0.5 kHz was excluded from the risk estimation. Hearing impairment was greater for the pure-tone frequency of 1 kHz than for that of 2 kHz. However, the mean hearing threshold was the poorest for 6 kHz, and the least effect was observed for 2 kHz. Our results suggest that toluene exacer- bates hearing loss in a noisy environment, with the main impact on the lower frequencies. Key words: adhesive products manufacturing, pure-tone audiometry, toluene, work-related hearing loss. Environ Health Perspect 114:1283–1286 (2006). doi:10.1289/ehp.8959 available via http://dx.doi.org/ [Online 26 April 2006] Premature hearing loss in industrial workers is a well-known outcome of noise exposure at work. Pryor et al. (1983) and Rebert et al. (1983) were the first to suggest that organic solvents also present an ototoxic effect in ani- mal studies. Barregard and Axelsson (1984) further suggested the possibility of an inter- action between solvents and noise intensifying hearing loss in workers. Studies were subse- quently conducted to examine the loss of audi- tory sensitivity due to organic solvents such as toluene, xylene, styrene, n-hexane, trichloro- ethylene, carbon disulfide, petroleum, and mixed solvents (Chang et al. 2003; Morata et al. 1993, 1995, 1997, 2002; Morioka et al. 2000; Sliwinska-Kowalska et al. 2001, 2004; Starck et al. 1999). Attention has also been focused on toluene because it is an organic solvent widely used in various manufacturing industries. The impair- ment from toluene exposure or simultaneous exposure to both toluene and noise has been established in animal models (Johnson et al. 1990; Lataye and Campo 1997; Lataye et al. 1999; McWilliams et al. 2000). Regarding human exposure to toluene, Morata et al. (1993) found that workers at a printing plant with exposure to both toluene and noise experienced 11 times greater risk for hearing loss at ≥ 25 dB. Morata et al. (1995) reviewed the dele- terious effect of toluene exposure on hearing function and identiﬁed gaps for further study. Schaper et al. (2003) conducted a follow-up study over 5 years with 333 male workers in rotogravure printing plants. With the mean (± SD) lifetime weighted average exposures to 45 ± 17 ppm toluene and 82 ± 7 A-weighted decibel [dB(A)] noise in the past and 26 ± 20 ppm toluene and 82 ± 4 dB(A) noise dur- ing the study, they found no signiﬁcant effect of toluene in hearing loss. Therefore, infor- mation is especially scarce on the threshold level of signiﬁcant effect. In the present study, more than half of the participating workers were employed at a plant that manufactured adhesive material and were exposed to toluene and/or noise for at least 10 years. The objective of this study was to evaluate the long-term effects of combined exposure to toluene and noise on audiometric thresholds. Materials and Methods Study subjects and data collection. We used a cross-sectional design that included interview- ing participants and measuring environmental exposure and hearing function in a plant man- ufacturing adhesive materials using toluene as a solvent. All workers in the adhesive materials manufacturing section with exposure to both toluene and noise were men, and all were invited to participate in this study; 58 men participated (response rate, 89.2%). We used Environmental Health Perspectives • VOLUME 114 | NUMBER 8 | August 2006 two reference groups: 58 male workers who worked in other sections of the plant and were exposed to noise only (response rate, 86.6%), and 58 male administrative clerks from the same company (response rate, 93.5%). Each participant provided informed consent, com- pleted a questionnaire for information on health history and lifestyle, and underwent a health examination and hearing test required by Taiwan labor law. This study was approved by the company and by the Council of Labor Affairs Institute of Occupational Safety and Health. No personal data were published. Toluene exposure assessments. On-site environmental toluene samples were collected and measured using U.S. National Institute for Occupational Safety and Health (NIOSH) method 1500 (Eller 1994; NIOSH 1984) by a contracted laboratory certiﬁed by the Taiwan Council of Labor. Air samples were collected for three divisions: adhesive materials manufac- turing division, application division, and recovery division. The on-site environmental air was pumped through a tube filled with 100 mg/50 mg (primary/backup) activated charcoal with a ﬂow rate of 20–200 mL/min. The adsorption tube samples were sealed using plastic caps, stored on ice, and sent for analysis. Samples were desorbed using carbon disulﬁde and analyzed using an HP 5890 gas chromatograph/flame ionization detector (Hewlett-Packard, Avondale, PA, USA) to measure the toluene levels in samples. Seven samples were collected from the breathing zone for each division. Hearing test and noise assessment. A soundproof booth built by the Institute of Occupational Safety and Health (IOSH), the Council of Labor, Taiwan, was assembled in a quiet area in the administrative ofﬁce. A physi- cian conducted the otopharyngeal examination to screen for otitis and other otopathy for exclusion from the study. Audiograms were Address correspondence to F.-C. Sung, Institute of Environmental Health, China Medical University College of Public Health, 91 Hsueh Shih Rd., Floor 15, Taichung 404, Taiwan. Telephone: 886-4-2205- 4070. Fax: 886-4-2201-9901. E-mail: fcsung@ mail.cmu.edu.tw This research was supported by the Executive Yuan Council of Labor Affairs grant IOSH2001-M363. The authors declare they have no competing ﬁnancial interests. Received 27 December 2005; accepted 25 April 2006. 1283