Combined Effects of Noise and Mixed Solvents Exposure on the Hearing Function among Workers in the Aviation Industry

Abstract

This study aims to evaluate the effect of occupational exposure to noise and organic solvents on hearing loss in the aviation industry. The study population comprised 542 male workers, who worked in avionics jobs in Kimhae, Korea, who kept records of work environment evaluations and medical examinations. The Cumulative Exposure Index (CEI) was constructed to assess the lifetime cumulative exposure of the workers, and pure tone audiometry(PTA) data of the workers from their biannual medical surveillance was used to assess hearing loss. The prevalence of hearing loss found in the group exposed to noise and mixed solvents simultaneously (54.9%) was higher than those in the other groups (6.0% in the unexposed, 17.1% in the noise-only, and 27.8% in the exposed to only a solvents mixture). The relative risks, adjusted for age, were estimated to be 4.3 (95% CI 1.7-10.8) for the noise-only group, 8.1 (95% CI 2.0-32.5) for the noise and solvents group, and 2.6 (95% CI 0.6-10.3) for the solvents-mixture group. These suggest that chronic exposure to mixed solvents had a toxic effect on the auditory system. This raises the issue of whether hearing conservation regulations should be applied to all workers exposed to solvents.

Exposure to Organic Solvent Mixture and Hearing Loss: Literature Overview

“…The subjects were classified as exposed to solvents when the cumulative index (exposure level × years) was higher than 10 (this corresponded to e.g. over 11 years' exposure to low solvent concentrations or over 3 years' exposure to high solvent concentrations) [1]. The method of biological monitoring (metabolites in blood and urine) was applied in one study [6].…”

“…The assessment concerned current and/or cumulative concentration of every single solvent and current and/or cumulative exposure index (the total sum of the ratios between solvent concentration and its threshold limit value, calculated for all solvents in the mixture). For toluene, the current exposure concentration in the air ranged from 0 to 70 ppm, for xylene it ranged from 0-417 ppm; and the current exposure index ranged from 0.5 to 23 [1][2][3]. The mean lifetime exposure (exposure level × duration of employment) to toluene ranged from 31-203 ppm, to xylene from 84 to 696 ppm, and exposure index from 10 to 67 [4,5].…”

“…Age, noise exposure, and employment duration were the variables included most frequently in the multivariate logistic regression models; in some studies, gender, alcohol consumption, hypertension, diabetes, smoking, noise trauma, and family history were also incorporated. As regards the risk assessment of hearing loss, a few studies evaluated this outcome at high frequency [1][2][3], some at all frequencies [4,5,9], and two at middle speech frequencies [7,8]. Eleven studies assessed the effect of solvent exposure on audiometric hearing threshold; five papers evaluated central effects on hearing (stapedial decay and contralateral stapedial reflex, interrupted and distorted speech, evoked cortical response, and cognitive response) [3,[13][14][15][16].…”

Perda auditiva associada à exposição ocupacional a solventes orgânicos: uma revisão sistemática

“…Most of the studies mentioned exposure to organic solvent mixtures at levels within local and/or international recommended tolerance limits 8,17,27,[30][31][32][33][34][35][36][37][38] . In those studies, noise exposure levels varied according to compliance with the tolerance limit of 85 dB(A) for an eight-hour working day, recommended internationally.…”

Frequency of the Audiometric Notch Following Excessive Noise Exposure

“…Overexposure to noise has been known to cause the occupational hearing loss. Such exposure is common in many industrial settings, such as construction, mining, agriculture, manufacturing and utilities, transportation, and the military (Kim et al, 2005). Occupational hearing loss resulting from exposure to high noise levels depends not only on the exposure time but also on the frequency, intensity, and type of noise, continuous or impact (Ahmed et al, 2001).…”