Audiometric findings of printing press workers exposed to noise and organic solvents

Effects of coexposure to noise and mixture of toluene, ethylbenzene, xylene, and styrene (TEXS) on hearing loss in petrochemical workers of southern China

Many harmful factors existing simultaneously with noise are reported to induce hearing impairment, such as organic solvents. However, the existing hearing safety limits and current risk assessment for hearing loss rely on single noise exposure. It is urgent to clarify the combined effect of noise and other harmful factors on hearing loss. Petrochemical workers are always exposed to noise and organic solvents, mainly benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS), while the combined effect of their coexposure on hearing remains unclear. Herein we conducted a cross-sectional survey, measuring pure-tone audiometry of 1496 petrochemical workers in southern China. Participants exposed to BTEXS were 569, 524, 156, 452, and 177 respectively. Individual cumulative noise exposure (CNE) levels and BTEXS exposure were assessed. The average CNE was 93.27 ± 4.92 dB(A)·years, and the concentrations of BTEXS were far below the occupational exposure limits of China. Logistic regression analyses showed that CNE was consistently positively associated with hearing loss (HL) and high-frequency hearing loss (HFHL) but not related to speech-frequency hearing loss (SFHL). Compared with participants in the lowest quartile of CNE, those in the highest quartile showed an OR of 5.229 (95% CI: 3.179, 8.598) for HFHL. Two-pollutant model analysis indicated that TEXS exposure was positively associated with HL (OR 1.679, 95%CI 1.086, 2.597), SFHL (OR 2.440, 95%CI 1.255, 4.744), and HFHL (OR 1.475, 95%CI 1.077, 2.020). However, no interactions were observed between CNE and TEXS coexposure on hearing loss. In our study, covariates including smoking and drinking status, body mass index (BMI), ear protection and personal protective equipment, and use of earphone/headphone were adjusted. In conclusion, coexposure to noise and low-level TEXS could induce more severe damage on hearing function than exposure to each alone, especially SFHL. Therefore, petrochemical workers simultaneously exposed to noise and TEXS, even at low-level, should be included in hearing protection programs.

Temporary and Permanent Auditory Effects Associated with Occupational Coexposure to Low Levels of Noise and Solvents

This study aimed to assess temporary and permanent auditory effects associated with occupational coexposure to low levels of noise and solvents. Cross-sectional study with 25 printing industry workers simultaneously exposed to low noise (<80 dBA TWA) and low levels of solvents. The control group consisted of 29 industry workers without the selected exposures. Participants answered a questionnaire and underwent auditory tests. Auditory fatigue was measured by comparing the acoustic reflex threshold before and after the workday. Workers coexposed to solvents and noise showed significantly worse results in auditory tests in comparison with the participants in the control group. Auditory brainstem response results showed differences in III−V interpeak intervals (p = 0.046 in right ear; p = 0.039 in left ear). Mean dichotic digits scores (exposed = 89.5 ± 13.33; controls = 96.40 ± 4.46) were only different in the left ear (p = 0.054). The comparison of pre and postacoustic reflex testing indicated mean differences (p = 0.032) between the exposed (4.58 ± 6.8) and controls (0 ± 4.62) groups. This study provides evidence of a possible temporary effect (hearing fatigue) at the level of the acoustic reflex of the stapedius muscle. The permanent effects were identified mainly at the level of the high brainstem and in the auditory ability of binaural integration.