Occupational toluene exposure and auditory function: results from a follow-up study.

The ototoxicity of occupational exposure to toluene below 50 p.p.m. was investigated in a longitudinal study over 5 yr with four repeated examinations starting with 333 male workers from rotogravure printing plants. Past lifetime weighted average exposures (LWAE) to toluene and noise were determined from individual work histories; recent individual exposures were measured 10 times during the study (toluene, active sampling; noise, stationary measurements). The auditory thresholds were measured with pure tone audiometry. The mean LWAE exposures to toluene and noise were 45 +/- 17 p.p.m. plus 82 +/- 7 dB(A) for printers (high toluene intensity) and 10 +/- 7 p.p.m. plus 82 +/- 4 dB(A) for end-processors (low toluene intensity). The mean current exposures to toluene and noise during the study were 26 +/- 20 p.p.m. plus 81 +/- 4 dB(A) for printers and 3 +/- 3 p.p.m. plus 82 +/- 4 dB(A) for end-processors. Repeated measurement analyses (grouping factors: toluene intensity, exposure duration and noise intensity) and logistic regressions did not reveal significant effects of toluene intensity, of exposure duration and of interactions between toluene intensity and noise intensity. The stratification dependent on noise intensity itself [79 +/- 3 versus 84 +/- 1 dB(A)] was significantly associated with the auditory thresholds. Regarding the missing toluene effects, it was concluded that the threshold level for developing a hearing loss as a result of occupational toluene exposure might be above the actual limit of 50 p.p.m.