Effect of Contemporary Exposure to Mixed Organic Solvents and Occupational Noise on Hearing Thresholds of Workers

Background: Mixed organic solvent exposure, as well as noise, has a wide spread in different industries. In recent years it has been propounded that simultaneous exposure to mixed organic solvents and occupational noise can establish a hearing loss that is more severe than hearing loss due to exposure to each of them separately.

  Materials & Methods: A descriptive- analytic study was conducted during 2008 in an automobile industry on 441 employees in three different groups. First group were assembly workers that only exposed to noise. The second group included employees in new painting saloon that exposed not only to noise but also to permissible levels of mixed organic solvents and the third group were employees in old painting saloon that exposed to noise and mixed organic solvents in more than threshold limit value (TLV) level. The prevalence of hearing loss was compared between three groups on the basis of model 1 (mean hearing threshold in frequencies 0.5, 1 and 2 KHz more than 25dB) and model 2 (mean hearing threshold in frequencies 3, 4, 6 and 8 KHz more than 25dB).

  Results: a ccording to model 2, in workers exposed to noise in addition to mixed organic solvents, the rate of hearing loss, was significantly higher than workers exposed to noise alone (P<0.05), even after adjusting for confounding variables using logistic regression analysis (OR= 4.12 , P<0.001).

  Conclusion: In workers with simultaneous exposure to mixed organic solvents and noise, special attention must be paid to accurate accomplishment of hearing conservation programs including doing audiometric exams in shorter periods and take advantage of hearing protection devices with higher noise reduction rate (NRR).