COMBINED EFFECTS OF NOISE AND STYRENE ON HEARING OF WORKERS AT A COMPANY FOR THE BATH AND TOILET PRODUCTION IN THAILAND

Combined exposure to both noise and aromatic solvents such as styrene is common in many industries. This study was aimed to clarify the combined effects of noise and styrene on hearing. The subjects were 199 workers (153 males and 46 females) at a company for bath and toilet production in Thailand. Group A (n=38, average age 36.3 years, average work experience 9.2 years) was exposed to noise and solvents. Group B (n=129, average age 36.2 years, average work experience 8.5 years) was exposed to noise. Group C (n=32, average age 37.6 years, average work experience 8.0 years) was officers. All subjects were asked to fill in a questionnaire on characteristics and working conditions. Audiometric threshold testing was performed at the frequencies of 0.5, 1, 2, 4 and 8 kHz in a meeting room. The noise levels and the organic solvents (styrene, acetone) concentrations in the working environment were measured. The results are as follows. The equivalent A-weighted noise level (LAeq) was 71.1-94.2 (average 83.7) dB in the Group A room. Forty-five percent of the Group A used no hearing protective equipment. Fifty-eight percent of them had hearing loss. Ninety-two percent of them used the mask for organic solvents. The styrene concentration was exceeding the occupational exposure limit (OEL) with 2 workers, but the acetone concentration was less than the OEL. The LAeq was 73.1-97.2 (average 84.0) dB in the Group B room. Seventy-two percent of the Group B used no hearing protective equipment. Sixty-four percent of them had hearing loss. There was no difference in the prevalence of hearing loss between Group A and Group B. In this study, the combined effects of noise and styrene on hearing were not clearly detected. However, the high prevalence of hearing loss suggests that the company should develop hearing conservation program for workers.