Role of free oxygen radicals in noise-related hearing impairment

This. study was aimed at defining the relationship between noise-related he aring impairment in industrial workers exposed to continuous noise. For thi s malondialdehyde and glutathione peroxidase were analyzed as free radical form and antioxidant form. A total of 60 patients working in the units of a hydroelectric power plant were included in the study. This experimental gr oup was further divided into three subgroups of 20 workers, each group expo sed to a different noise level. The control group consisted of 20 male volu nteers employed in the Medical Centre where the study was carried out. A st andard ascending/descending method was applied to the subjects of the exper imental and the control groups in order to determine their hearing threshol ds at seven different frequencies between 250 and 8000 Hz. Then, 10 ml bloo d was collected from each person to measure the malondialdehyde values in p lasma and glutathione peroxidase activity in erythrocytes. Slight sensorine ural hearing impairment was found in group I beginning at 4 kHz and in grou p II beginning at 6 kHz. Statistically significant differences were observe d in group I and II when compared to the control group (P < 0.05). It was f ound that malondialdehyde levels increased in the experimental groups more than in the control groups. However, this increase was only significant in group I (P < 0.05). Erythrocyte glutathione peroxidase activity significant ly increased in group I and II compared to the other groups (P < 0.05), als o, the difference was significant between group I and II (P < 0.05). Accord ingly, it is suggested that free oxygen radicals may take a role in noise-r elated hearing impairment. (C) 2001 Elsevier Science B.V. All rights reserv ed.