A survey of the effect of toluene on the impact of noise on hearing loss in workers

Background: Ototoxic chemicals can impair the sense of hearing and balance. In the past decades, the ototoxicity of solvents and their interaction with noise have become evident. This study has been carried out in the shoe manufacturing factory in Tehran (Iran) with the aim of evaluating the combined effects of noise and toluene on the workers' hearing. Materials and Methods: This cross-sectional and analytical study was conducted on 64 workers selected through census. The participants were assigned to 3 groups according to their exposure to noise and toluene. Group 1 consisted of 33 workers who were exposed to noise, group 2 of 5 exposed to toluene, and group 3 of 26 exposed to noise and toluene. Toluene concentrations were measured in the workers' breathing zone as well as A-weighted sound pressure level (SPL), overall noise level (LpA) and equivalent continuous A-weighted SPL over 30 minutes, and the equivalent noise level A (LeqA) in the head position of workers. Then, the noise level was calculated and hearing thresholds were measured in 500-4000 Hz frequency range. The amounts of air and bone hearing loss were also calculated. Results: The results indicated that the relationship between hearing loss caused by noise (group 1) and noise and toluene (group 3) were statistically significant (P < 0.50). Hearing loss due to toluene in midrange frequencies was more pronounced than in high frequencies. Conclusions: The results of the study suggest that authorities should pay greater attention to agents such as noise which affect the hearing loss and health of employees, especially with respect to sensitivity of hearing system disorders. Moreover, individual characteristics should also be considered in employing future personnel.