Mixed solvent exposure and hearing impairment: an epidemiological study of 3284 men. The Copenhagen male study

Animal experiments and human studies have indicated an effect on auditory functions from exposure to organic solvents. In this study the relationship between self-assessed hearing problems and occupational exposure to solvents was investigated in a cross-sectional design with 3284 participating men aged 53-74 years. Exposure to solvents for five years or more resulted in an adjusted relative risk (RR) for hearing impairment of 1.4 (95 per cent CI: 1.1-1.9) in men without occupational exposure to noise. Factors adjusted for were age, noise traumas, chronic middle ear infection and family history of hearing impairment. The prevalence of hearing impairment in men not exposed to organic solvents was 24 per cent and the attributable risk from solvent exposure was 9.6 per cent. Exposure for less than five years had no effect on hearing capacity. Occupational exposure to noise for five years or more had an effect twice that of solvents, RR: 1.9 (95 per cent CI: 1.7-2.1). In men exposed to both solvents and noise the effect of the latter dominated and no additional effect from solvents was found. A subsample of 51 men was examined with pure tone audiometry and 20 of 21 men who reported abnormal hearing also fulfilled an audiometric criterion for hearing impairment. In conclusion a damaging effect on hearing ability from long-term solvent exposure was found in the present study. The relative effect was moderate but with a high background frequency of hearing problems in the unexposed sample the absolute effect, ie attributable risk, was considerable and of both clinical and preventive importance.