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EC number: 905-570-2 | CAS number: -
The auditory function of 30 medical laboratory workers (15 males and 15 females) who had been exposed to a mixture of xylene isomers was compared to that of 30 non-exposed workers matched for gender, age, and educational level. Participants of both groups were not exposed to noise levels above 85 dBA time-weighted average. All participants were evaluated in a sound-treated room, using a comprehensive audiological test battery, which included measures of peripheral and central auditory function. Xylene-exposed participants were evaluated before their shift commenced, approximately 16 hours after their last exposure. Airborne xylene samples were collected at 11 different work stations throughout the 9 histology laboratories studied. The mean airborne xylene concentration was 36.5 mg/m3. Urine samples were collected from each xylene-exposed worker and the methyl hippuric acid concentration was determined. The mean concentration of methyl hippuric acid was 216.3 mg per gram of creatinine in urine. Noise dosimetry was also performed on each xylene exposed subject and the mean daily noise exposure level was 72.9 dBA. The xylene-exposed participants showed significantly worse pure-tone thresholds in comparison with the nonexposed participants. The xylene-exposed participants demonstrated significantly worse results than the control group participants for the pitch pattern sequence test, dichotic digit test, speech recognition in noise test, and the auditory brainstem response (absolute and interpeak latencies). A significant correlation between the concentrations of methyl hippuric acid in urine and binaural average hearing level (2 to 8kHz) was found in xylene-exposed workers. Also, participants with high cumulative dose of xylene exposure presented with poorer test results than participants with low cumulative dose of xylene exposure. The results of the study provide limited evidence that xylene may induce a decrement in pure-tone hearing thresholds as well as in some central auditory nervous system functions such as temporal ordering, binaural integration, and speech perception in noise, but dose-response relationships were not observed between xylene exposure and the outcomes for central auditory nervous system function. It could not be determined whether the adverse effects are acute or permanent. Outer hair cell dysfunction is not indicated by the nonsignificant differences in DPOAE amplitudes between xylene-exposed and nonexposed.
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