**1. Introduction**

170 Hearing Loss

[26] Toner, J. G. and Kerr A. G. Ear Trauma. Scott- Brown's Otolaryngology. Otology 6th

Butterworths Meinemann, London 1997: 3/711-3/7/13.

Edition Edited by J. B. Booth, General Editor Kerr, A. G. Advisory Editor Groves,J.

Exposure to chemicals in the workplace can lead to occupational chemical-induced hearing loss, as many chemicals have been internationally recognised as hazardous to hearing. A number of studies have demonstrated that, similar to noise, some chemicals not only affect the sensory organ of the auditory system (the cochlea) but also lead to adverse effects in central auditory structures. Morata and Lemasters (1995) suggested that the adverse auditory effects of chemicals such as solvents are due to a combination of oto-and neurotoxicity. Oto-toxicity induces outer hair cell (OHC) dysfunction in the cochlea (similar to the effects of noise), whereas neuro-toxicity induces central auditory dysfunction. The main audiological sign of oto-toxicity is poorer hearing thresholds than expected relative to age. Audiological signs of neuro-toxicity may or may not include poorer hearing thresholds, in addition to difficulties discriminating sounds, such as speech, particularly in adverse listening conditions.

The aim of this review is to provide an in-depth discussion of occupational chemicalinduced hearing loss, taking into consideration ototoxic agents such as solvents, pesticides and metals, and their interaction with noise. Contemporary findings from research conducted in animals and humans are included here. Also, research findings from the authors with regard to the effect of exposure to mixtures of solvents on the peripheral and central auditory system will be addressed. Finally, in the section on international legislation of occupational chemical-induced hearing loss, a review of current legislation in a number of countries is presented.
