Effect of combined occupational exposure to noise and organic solvents on hearing

Noise exposure has been commonly regarded as the main hazard of occupational hearing loss. Recent studies indicate that several chemicals, including organic solvents have ototoxic effects. This study aimed at evaluating the hearing of workers exposed to both noise and a mixture of organic solvents at concentrations anticipated as safe. The study comprised three groups. The first one included 70 workers exposed to noise only, the second group consisted of 93 workers exposed to organic solvents and noise, and the control group included 59 individuals exposed to neither noise nor organic solvents. The three groups were matched for age, socioeconomic status, and smoking habit. The results of this study revealed that there was no statistically significant difference between the two exposed groups as regards the duration of exposure. There was a highly statistically significant difference between the two exposed groups as regards the different types of hearing loss (conductive deafness, sensory neural hearing loss, and mixed type) compared with the control one. Our study reported that sensory neural hearing loss occurred earlier in subjects with combined exposure to noise and solvents at a mean duration of exposure (16.38 +/- 9.44 years) compared to (24.53 +/- 9.59 years) the subjects with sole exposure to noise. The difference between the two groups was statistically significant regarding this type of hearing impairment (p < 0.05). There was a positive significant correlation between hearing impairment and duration of exposure in the two exposed groups. As regards the results of the environmental monitoring, both noise exposure levels (dB) and levels of different organic solvents measured (mg/m(3)) in different work departments were less than the levels recommended by Egyptian Environmental Law No. 4 for 1994. It is recommended that in the case of combined exposure, noise and solvent levels should be lowered than the permissible limits recommended for either alone.