Effects on hearing and on balance of co-exposure to low-frequency-rich noise and to a solvent: the carbon disulphide (CS2) model

At workplaces, noise that is low-frequency rich is omnipresent and it can be associated with solvents, such as carbon disulphide, for example. That solvent, which is used in manufacturing cellulose and more particularly viscose, is known to give rise to hearing losses in the low frequencies. In this type of co-exposure, it is legitimate to question the relevance of the daily exposure levels averaged over 8 hours (LEx,d) recommended for noise on its own, and the relevance of the occupational exposure limit values (OEL values) and short-term OEL values (OEL/ST values) recommended for solvent on its own. Noise could potentiate the ototoxicity of the solvent, and vice versa. Unlike for hearing, the data in the literature relating to the impact of solvent on balance is almost inexistent.

The objectives of this study will thus be to check whether the limit values recommended for noise and for CS2 are sufficiently protective of the vestibule and of the cochlea during exposure combining both solvent [(6 X 15 minutes)/day at 250 ppm] and continuous noise that is rich in low frequencies [85 dB, 6 hours/day]. In addition, understanding the mechanisms leading to a hearing deficit in the low frequencies would make it possible to distinguish between injuries caused by noise (auditory scotoma centred on 4 kHz) and injuries inherent to CS2 intoxication (0.5 kHz to 2 kHz). This study will be conducted by measuring acoustic distortion products and auditory nystagmus in the Norway brown rat.
The study will involve collaboration with a Spanish team specialised in vestibulotoxicity.

Planned dissemination: In addition to publications in peer-reviewed international journals, and to recommendations relating to LEx,d, OEL and OEL/ST values, the prospects for transferring these two techniques to humans will be considered.