Abstracts of the Twenty-Third Annual Mid-Winter Research Meeting of the Association for Research in Otolaryngology. Popelka GR, ed., St. Petersburg Beach, FL: Association for Research in Otolaryngology, 2000 Feb; :25
The aim of this cross sectional study was to investigate the effects of occupational exposure to styrene and noise on the auditory system. The study protocol included a questionnaire, assessment of styrene and noise exposures, and an extensive audiologic battery. The group consisted of workers exposed to styrene and noise (n=150), noise alone (n=75) or unexposed controls (n=60). The questionnaire included questions on work history, non-occupational solvent and noise exposure, and medical history. Exposure assessment included gathering data from interviews and company records, and site measurements of noise levels for different work tasks. Styrene measurements were conducted on all exposed workers by air samples and biological monitoring of mandelic acid in urine.The audiologic test battery was comprised of pure-tone audiometry (0.5-8 kHz Bekesy audiometry), distortion product otoacoustic emissions (input/output function at levels 35-80 dB SPL at 4 kHz), psycho-acoustical modulation transfer function (top and valley thresholds between 35-105 dB HL at 4 kHz with 10 Hz modulation noise), interrupted speech (7 interruptions/sec), speech recognition in noise (signal/noise ratio measurements of sentences; Hagerman, 1982), and cortical response audiometry (latency of N1-component after stimuli of frequency glides of a 1000 Hz tone at 60 dB HL).About 60% of the participants in both groups exposed to noise (styrene/noise and noise alone) were exposed to noise levels above the Swedish threshold limit value (85 dBA/3 dB exchange rate) and the range of exposure was also similar in these groups (75-116 dBA). The styrene exposure was low, averaging 3.5 ppm with a maximum level of 22 ppm, (8 h values, TLV (8h) in Sweden is 20 ppm). High frequency hearing loss (> 25 dB at more than one frequency above 2 kHz) was present in 47% of the workers exposed to styrene and noise, compared to 42% of the workers exposed to noise alone and 35% of the controls.