High level styrene exposure aggravated effects of noise on hearing

Objective To explore the synergistic effect of occupational exposure to both high level styrene and noise on pure tone hearing.

Methods A total of 114 workers (as study group) who were occupationally exposed to both high concentration styrene and noise and 97 workers (as reference group) who were only exposed to noise in a sports equipment enterprise were studied. The exposure levels of styrene and noise were evaluated and their hearing examination results were analyzed.

Results The time weighted average concentration (TWA) of styrene in the air at study group's workplaces was (402.81±52.25) mg/m³ with the complacence rate of 16.67% compared with national OEL. The exposure level of noise (L_{EX, 8 h}) was (87.1±1.1) dB (A) in the study group and (86.7±1.0) dB (A) in the reference group, respectively and there was no significant difference (P>0.05). The abnormal rate of hearing loss in the study group was 19.2%, while 8.2% in the reference group. The average high frequency hearing threshold of workers in the study group was (28.3±9.0) dB, while (25.0±2.7) dB in the reference group. The abnormal rate of high frequency hearing loss in the study group was higher than that in the control group. There was a significant trend that higher exposure to styrene higher abnormality of high frequency hearing loss, the abnormality was 6.5%, 25.0%, 47.6% in 3 sub-groups divided according to workers' exposure level of styrene (lower than 213 mg/m³, 213~426 mg/m³, and higher than 426 mg/m³), respectively.

Conclusion High concentration of styrene could increase the risk of hearing damage, which may have a certain synergistic effect with noise. In order to protect the health of workers' hearing system, we should replace styrene with non-toxic or low toxic substances and reduce the exposure time of noise.