Audiometric Findings in Workers Exposed to Low Levels of Styrene and Noise

Learning Objectives Explain whether and how exposure of workers to styrene in the course of making fiberglass products, and to high noise levels, interact to produce bilateral high-frequency hearing loss. Recall the personal and environmental factors that were significantly associated with hearing loss in this study. Discuss how these findings relate to past studies in animals and styrene-exposed workers, and take note of relevant public health considerations. 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.