How to explore the otoneurotoxicity of solvents in the framework of epidemiological studies in the work environment

Organic solvents are used in the industrial environment, and the combined exposure to noise and solvents (pure or in mixtures) is of concern to numerous workers from various economic sectors.
Although the effects of organic solvents on the central nervous system are well known, their sensorineural effects, particularly in the auditory system, constitute a new area for research. Studies conducted with experimental animals have shown that the combined exposure to solvents and noise results in a synergistic effect on the auditory system, and that the lesions can be both cochlear and retrocochlear. In humans, there is now evidence from epidemiological studies in the occupational environment suggesting an ototoxic effect of some single solvents and solvent mixtures, as well as evidence of an interaction between noise and solvents on the auditory function.
To study these ototoxic effects in the framework of epidemiological studies in work environments, it is necessary to customize a test battery. Such a battery must be subject to the following constraints: tests must contribute to the determination of the proportion of the lesion attributable to the ototoxic properties of the solvents; they must meet criteria expected from epidemiologic studies (reproducibility and sensitivity); and it should be possible for them to be performed in the work environment, with workers who a priori are asymptomatic.
Two different audiological batteries have been developed by Swedish research groups (Odkvist et al., 1987; Johnson et al., 1998). Both batteries use speech material that is not available in French. This report outlines the development of a test battery in French, which is comparable to the Swedish batteries, taking into consideration the pertinence and quality of tests, their feasibility, and the availability of French speech materials.
The test battery proposed in this report consists of pure-tone audiometry using the Hughson Westlake technique (Portmann and Portmann, 1988), speech audiometry in noise as proposed Hagerman (1982), interrupted speech audiometry with lists adapted from Fournier (Portmann and Portmann, 1988), stapedius reflex testing, and the distortion product otoacoustic emissions.