The effects of toluene plus noise on hearing thresholds: an evaluation based on repeated measurements in the German printing industry.

OBJECTIVES The ototoxicity of occupational exposure to toluene plus noise was investigated in a longitudinal study in rotogravure printing and existing findings in the literature were evaluated. MATERIAL AND METHODS The study comprised four repeated examinations during 5 years and started with 333 male workers. Lifetime weighted average exposures (LWAE) to toluene and noise were determined from individual work histories and historic recordings; recent individual exposures were measured 10 times during the study (toluene, active sampling; noise, stationary measurements). Auditory thresholds were measured with pure tone audiometry at 0.125, 0.25, 0.5, 0.75, 1, 2, 3, 4, 6, 8, 12 kHz. RESULTS Mean LWAE exposures to toluene and noise were 45+/-17 ppm plus 82+/-7 dB(A) for high toluene exposed and 10+/-7 ppm plus 82+/-4 dB(A) for low toluene exposed subjects, mean current exposures were 26+/-20 ppm plus 81+/-4 dB(A) and 3+/-3 ppm plus 82+/-4 dB(A). Mean exposure duration was 21.3+/-6.5 years for long exposed and 5.9+/-2.2 years for short exposed subjects. Repeated measurement analyses of variance did not reveal effects of toluene intensity, exposure duration and interactions between toluene intensity and noise intensity. Noise intensity [79+/-3 dB(A) vs. 84+/-1 dB(A)] was significant for auditory thresholds. A case concept utilising developments of individual auditory thresholds did not reveal significant toluene effects. Logistic models including age, exposure duration, toluene in ambient air, current noise and either hippuric acid or ortho-cresol (o-cresol) found only age to be significant for elevated OR of high frequency hearing loss. CONCLUSIONS Due to missing toluene effects, it was concluded that the threshold level for developing hearing loss as a result of occupational exposure to toluene plus noise might be above the current limit of 50 ppm toluene.