Audiometry and exposure measurements were conducted on workers from fiberglass and metal products manufacturing plants and a mail distribution terminal (N = 313). Workers exposed to noise and styrene had significantly worse pure-tone thresholds at 2, 3, 4, and 6 kHz when compared with noise-exposed or nonexposed workers. Age, noise exposure, and urinary mandelic acid (a biologic marker for styrene) were the variables that met the significance level criterion in the multiple logistic regression. The odds ratios for hearing loss were 1.19 for each increment of 1 year of age (95% confidence interval [CI], 1.11-1.28), 1.18 for every decibel >85 dB(A) of noise exposure (95% CI, 1.01-1.34), and 2.44 for each millimole of mandelic acid per gram of creatinine in urine (95% CI, 1.01-5.89). Our findings suggest that exposure to styrene even below recommended values had a toxic effect on the auditory system.

Audiological testing, interviews and exposure measurements were used to collect data on the health effects of styrene exposures in 313 workers from fiberglass and metal-product manufacturing plants and a mail terminal. The audiological test battery included pure-tone audiometry, distortion product otoacoustic emissions (DPOAE), psychoacoustic modulation transfer function, interrupted speech, speech recognition in noise and cortical response audiometry (CRA). Workers exposed to noise and styrene had significantly poorer pure-tone thresholds in the high-frequency range (3 to 8 kHz) than the controls, noise-exposed workers and those listed in a Swedish age-specific database. Even though abnormalities were noted on DPOAE and CRA testing, the interrupted speech and speech recognition in noise tests were the more sensitive tests for styrene effects. Further research is needed on the underlying mechanisms to understand the effects of styrene and on audiological test batteries to detect changes in populations exposed to solvents.

Biochemical markers for the circadian rhythm were studied in patients treated at the ICU (intensive care unit) of two regional hospitals. A normal rhythm is characterized by a relatively higher melatonin and a lower cortisol excretion at night. Disturbances affect sleep, mood and cognitive performance. All urine excreted between 07:00 and 22:00 hours (day) and between 22:00 and 07:00 hours (night) was collected and sampled throughout the entire ICU period (median, 10 days) in 16 patients for the excretion of 6-SMT (6-sulphatoxymelatonin), which is a metabolite of melatonin, and free cortisol. The overall excretion of 6-SMT was slightly lower and the cortisol excretion higher than reported for healthy reference populations. Mechanical ventilation was associated with a markedly lower 6-SMT excretion (median, 198 ng/h) compared with periods without such help (555 ng/h; P<0.0001), whereas infusion of adrenergic drugs increased the 6-SMT excretion (P<0.01). Five patients (31%) showed a virtually absent melatonin excretion for 24 h or more. The diurnal rhythms were consistently or periodically disturbed in 65% and 75% of the patients. These alterations cannot be explained by excessive exposure to light at night. In conclusion, there was hyposecretion of melatonin during mechanical ventilation, an overall high cortisol excretion and a disturbed diurnal rhythm of both of these hormones in most patients treated in two ICU departments.

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