The ototoxicity of styrene: a review of occupational investigations.
OBJECTIVE
The objective of this study was to review critically a number of occupational investigations of the exposure and effect relation between inhaled styrene vapour and hearing loss. There is concern that workers' hearing may be impaired by exposure to styrene, as used in industries making plastics and fibreglass-reinforced products.


METHODS
Seven occupational studies, each dealing with the ototoxicity of styrene, were examined. Factors assessed included the experimental design and number of subjects within exposure groups, measurement of the styrene-in-air concentration, confirmation of the styrene exposure by blood or urine analysis, determination of the hearing threshold levels for the exposure and control groups, and measurement of any occupational noise in the subjects' workplaces. Consideration was also given to statistical relations between high-frequency hearing loss and lifetime exposure indices for styrene and noise.


RESULTS
The results are equivocal. Four investigations failed to find any effect of styrene on hearing thresholds. In contrast, other investigations claimed to have demonstrated styrene-induced hearing loss in industrial populations, with synergism between styrene and noise. However, these reports exhibited shortcomings of experimental design and data analysis.


CONCLUSIONS
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.
Lawton
B W
BW
Institute of Sound and Vibration Research, University of Southampton, University Road, Highfield, SO17 1BJ, Southampton, United Kingdom. bwl@isvr.soton.ac.uk
Hoffmann
J
J
Triebig
G
G
D003718:Denmark; D034381:Hearing Loss / Q000209:etiology*; D006801:Humans; D019570:Inhalation Exposure; D016273:Occupational Exposure; D020058:Styrene / Q000506:poisoning*
D020058:Styrene