Investigation on combined effects of exposure to toluene and occupational noise on hearing loss

Objective To study the combined effects of exposure to toluene and noise on hearing loss. Methods Totally 78 workers occupationally exposed to both toluene and noise, 75 workers exposed to only noise and 90 workers without any records of occupational exposure from two companies in Zhuhai City were studied. The toluene concentration and noise level at workplaces were measured. Pure tone test were done for all workers with pure tone audiometry. Results The average noise level was 89.1±9.3 and 88.6±6.2 dB(A) at workplaces of two exposed groups respectively and the toluene concentration was 56.4-143.0 mg/m³. The workers in combined exposure group had higher abnormality of hearing threshold at frequencies of 3.0, 4.0 and 6.0 kHz than the workers exposed only to noise(q=4.404, 3.315, 4.253,P<0.05). The hearing loss both at speech frequency and high frequency among combined exposed workers was more serious, and the abnormality was 25.6% and 51.3%,respectively, while 22.7% and 24.0% among only noise exposed workers. The workers with combined exposure longer than 5 years had particular higher abnormality than workers with only noise exposure longer than 5 years (P<0.05). Conclusion There might be a synergistic effect of occupational exposure to both toluene and noise on hearing loss, the professional safety protection should be considered.