Objective To analyze the effects on hearing loss of workers exposed to both benzene series and noise, and to provide theoretic basis for developing related national hygienic standard.
Methods The study recruited 71 male workers who were exposed to both low-level benzene series (toluene < 40 mg/m3) and noise (low combined exposure group), 96 male workers who were exposed to both high-level benzene series (toluene ≥ 40 mg/m3) and noise (high combined exposure group), and 153 male workers exposed to noise only (noise only group). Personal sampling techniques were used to measure the levels of benzene series and noise exposure at workplaces. Pure-tone audiometry tests at 6 frequencies of 0.5, 1, 2, 3, 4, and 6 kHz were used to access hearing thresholds. Cumulative noise exposure (CNE) was calculated for stratified analysis.
Results The prevalence of highfrequency hearing loss in the high combined exposure group (66.67%) was much higher than that in the low combined exposure group (28.17%) and in the noise only group (37.25%). A significant dose-response relationship was observed between CNE and the prevalence of high-frequency hearing loss in each group. The results of logistic regression analysis showed the left shifted and slope elevated dose-response curves for both combined exposure groups were identified comparing to the curve of the noise only group.
Conclusion The results suggest that benzene series exposure in noisy working places can elevate the prevalence of hearing loss in male workers, mainly inducing high-frequency hearing loss.
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