The effects of occupational exposure to styrene on high-frequency hearing thresholds

Subchronic exposure to styrene has been reported to produce high-frequency hearing loss in rats. In humans, hearing thresholds for higher frequencies (greater than 8 kHz) are also more vulnerable to ototoxic drugs than those at lower frequencies. Since hearing loss at frequencies above 8 kHz does not seem to play a role in speech processing, hearing loss at frequencies above 8 kHz in workers exposed to styrene or other solvents might easily escape detection. Therefore, hearing thresholds were evaluated at frequencies up to 16 kHz in workers exposed to styrene and compared to those of a control group of unexposed workers. The airborne concentrations of styrene typically did not exceed 150 mg/m3 although individual exposures did, at times, reach higher values (up to 700 mg/m3). In accordance with the literature, an age-dependent increase in hearing thresholds at high frequencies was found. Compared to controls, workers exposed to styrene did not appear to demonstrate an aggravated age-dependent decrease in hearing high frequencies. A comparison, however, within the experimental group between the least exposed and the most exposed workers revealed a statistically significant difference on hearing thresholds at high frequencies.