Styrene is largely used in the polystyrene-plastic industry. High exposures can occur in reinforced-plastic industry, especially in the production of large items such as boats, which involve manual lay-up and spray-up operations 1,2) .In experimental studies an ototoxic effect of high styrene concentrations could be demonstrated in rats 3) . Morphological analysis by light and electron microscopy revealed a severe loss of outer hair cells in the third row, particularly in the upper basal and lower middle regions of the cochlea. The threshold for this effect appears to be between 300 and 600 ppm 4) . Furthermore there are hints from new studies, that combined exposures to styrene and noise may act synergistically in rats 5) . The results of studies addressed to the potential effect of styrene exposures on hearing loss in humans at workplaces are equivocal [6][7][8][9][10][11][12] .The purpose of this study was to examine, whether styrene exposure at typical industrial workplaces is associated with reduced hearing ability in exposed workers or not. In the search for some effect of styrene upon human hearing most of the investigators used hearing threshold levels in pure-tone audiometry to quantify any loss of hearing ability. This traditional approach may not be sufficient or reliable to investigate the effects of styrene exposure on auditory function. Therefore we also measured transient (click) evoked otoacoustic emissions (TEOAE) to study cochlear function with a sensitive, noninvasive and objective manner in addition to conventional pure-tone audiometry.The study population consisted of 32 male workers of a boat building factory. Out of them, 16 laminators were regularly exposed to styrene vapours. Mean duration time of styrene exposure was 8 yr (standard deviation (SD) 5). With regard to age, reported previous noise exposure and socio-economic status, the 16 subject of the control group were comparable to the exposed workers. Control persons were not directly exposed to styrene or other chemicals. The mean age was 41 (SD 8) yr in the laminator group and 39 (SD 8) yr in the control group.Data collection consisted of interviews in which each worker was asked about previous affections of the ear, Abstract: Objectives: We conducted this study to examine, whether occupational styrene exposures are associated with reduced hearing ability. Methods: The auditory function was investigated by pure tone audiometry and registration of transitory evoked otoacoustic emissions (TEOAE) in 32 workers of a fibre-reinforced plastic boat building factory. Sixteen subjects were laminators (mean age: 41 yr (SD: 8)) and therefore regularly exposed to styrene with mean duration of exposure to styrene of 7.5 yr (SD 5.0). The tests were applied to a reference group of 16 workers (mean age: 39 yr (SD: 8)) who were not directly exposed to styrene but had a similar noise exposure. Results: A few and isolated correlations between the parameters of hearing acuity and exposure indices, such as current internal styrene exposures (sum of MA a...
Considering the body of evidence as a whole, hearing deficits due to occupational exposure to styrene at low concentrations have not been demonstrated by scientifically reliable argument. There is some suggestion of an association between styrene exposure, occupational noise, and hearing dysfunction. Further studies in humans are necessary to clarify this question.
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