Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Prolonged significant noise exposures are well known to result in permanent hearing loss. However, little is known of the contribution of industrial chemical exposures to hearing loss. Information available, both from 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 fibre 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 was obtained from each participant on factors including: 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 important relationships were observed between styrene exposures and changes in hearing acuity over the course of the workshift. Therefore, styrene does not appear to exert an acute effect on hearing, at exposure levels which were generally within the current standards. Similarly, no conclusive evidence was found for a chronic styrene-induced effect on hearing acuity, when both noise and styrene 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, suggesting a synergistic effect. Noise and styrene exposures were highly correlated, clearly illustrating the importance of considering all associated variables in analysis of such data. No conclusive evidence was found for a relationship between smoking, recreational noise, other solvent exposures and hearing loss. Further, the study highlighted the difficulties in constructing retrospective exposure indices when actual, historical measurements are lacking and reliance must be placed on alternative methods such as questionnaire responses from individual subjects.



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