An investigation of the association between exposure to styrene and hearing loss

The importance of the association between advancing age and hearing loss is well recognized. Further, prolonged significant noise exposures are also known to result in permanent hearing loss. However, little is known of the contribution of industrial chemical exposures to hearing loss. Information available, from both animal and human studies, raises the possibility that certain aromatic hydrocarbons are ototoxic. The purpose of this study was to assess whether occupational styrene exposure causes hearing loss in a group of workers in the fiber-reinforced plastics manufacturing industry. The hearing acuity of 299 subjects was determined, using pure-tone screening audiometry, at the beginning of a single workshift and again at the end of the shift. On the same day, the personal, time-weighted average exposures of each subject to both styrene and noise were measured. In addition, information on the following factors was obtained from each participant: previous work history, including exposures to noise and chemicals; use of personal protective equipment for noise or solvents; personal and family history of hearing problems; and smoking history. Current exposures together with work histories were used to construct lifetime noise and styrene exposure indices. No conclusive evidence was found for a chronic styrene-induced effect on hearing acuity, when both noise and styrene lifetime exposures were taken into account. As expected, age and noise exposures were highly important variables, both positively associated with hearing loss. In addition, the detrimental effect of noise exposure on hearing acuity was found to be strengthened with increased age. Noise and styrene exposures were highly correlated, clearly illustrating the importance of considering all associated variables in analysis of such data. No evidence was found for a relationship between smoking, recreational noise, solvent exposures, and hearing loss.