Combined effects of occupational exposure to noise and organic solvents on the auditory system

Noise exposure is the most common cause of hearing loss. In many work environments where organic solvent exposure occurs, a high level of noise exposure is also common. However, as to the ototoxic effects of organic solvents, the earlier studies focused on the exposure to an organic solvent alone. It is necessary to clarify the combined effects of exposure to noise and organic solvents at the simulated situation of the work environments. The objective of this study was to review the literature on the ototoxic effects of exposure to organic solvents combined with noise. Two organic solvents were selected: methanol, a widely used organic solvents in the occupational field, and styrene, also widely used and a human neurotoxicant. Judging from the results of animal experiments and epidemiologic studies, a synergistical interaction of noise with such organic solvents’ ototoxicity was clarified even at the lower concentration where the organic solvent alone showed no ototoxicity in the experimental animals and at the concentration lower than the occupational exposure limits of organic solvents. Consequently, it is important to carefully access the occupational exposure limits when workers are exposed to organic solvents combined with noise, and to take measures against combined exposure.