RESUMO
Noise induced hearing loss is one of the most common and expensive sources of compensated work related health problems in modern industrialized countries. This study was conducted to detect the combined effect of occupational exposure to noise and lead on hearing. An observational analytic comparative approach was selected for this study. The inference population comprised 208 production workers from the Egyptian Copper Works Company in Alexandria, of these workers 51 were exposed to both noise and lead, 54 workers were exposed to noise, 53 workers were exposed to lead, and the rest, 50 workers were not exposed to neither noise or lead. All workers were subjected to a detailed interview, physical examination, otological examination, and auditory evaluation through a pure-tone audiometry, speech audiometry [Speech Reception Threshold [SRT] and Speech Discrimination Score [SDS]%], tympanometry, and auditory brain-stem response audiometry. Moreover, the blood lead level of workers, and workplace noise intensity were measured. Clinical evaluation of workers revealed a significant increase in mean systolic blood pressure among lead exposed and noise exposed workers. Neurological manifestations [tremors, tingling/numbness, reduced visual acuity and headache], urinary troubles, and oral manifestations gingivitis and bleeding gum], were significantly more encountered among lead exposed workers and workers with combined exposure. On assessing the workers' mean hearing threshold of the right ear, it was evident that at low frequencies [250 Hz and 500 Hz] the maximum significant drop was recorded among the workers with combined exposure [30.2 +/- 9.8 dB, 30.2 +/- 9.74 dB respectively], compared to lead exposed workers [29.15 +/- 8.42 dB, 28.49 +/- 6.97 dB respectively], and noise exposed workers [27.68 +/- 6.98 dB, 28.43 +/- 7.57 dB]. On the contrary, at higher frequencies [1 KHz - 8 KHz] the maximum drop was recorded by noise exposed worker. Regarding the left ear, the maximum impairment at low frequencies was observed among lead exposed workers [28.3 +/- 8.08 dB, 28.49 +/- 9.38 dB respectively], but at the higher frequencies a similar pattern to that observed at the right ear was obtained. Noise exposed workers had the most impaired mean SRT [31.48 +/- 8.22 dB], while workers with combined exposure recorded the worst mean SDS% [91.67 +/- 6.06%]. No significant delay was observed in the Auditory Brainstem Response [ABR] audiometry recorded at the latencies I, III, and V and inter-peak latencies; I-III, I-V, and III-V for the studied workers. On calculating the total hearing impairment percent, noise exposure imposed the worst effect on hearing, where both noise exposed workers and workers with combined exposure had the highest mean hearing impairment percent [15.25 +/- 13.61%, 13.22 +/- 13,49% respectively]. Among noise exposed workers, the significant predictors of hearing impairment were the duration of employment and smoking. While, blood lead level and aging were the significant predictors for hearing impairment among workers with combined exposure. Cochlear affection is the main site of lesion in noise and/or lead exposed workers, and the risk of combined exposure to noise and lead imposed on the auditory system sensitivity at the studied levels of exposure is nearly similar to that encountered by noise exposure alone