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Description of key information

Ototoxicity is known to occur following repeated inhalation exposures to toluene, styrene and ethylbenzene. Effects on colour vision in humans have also been reported for toluene and styrene. These effects are considered in the overall risk assessment for repeated dose exposures in section 5.6.3.

Additional information

The specific components toluene, styrene and ethylbenzene are recognised as ototoxicants following repeated inhalation exposure. Effects on colour vison have also been reported for toluene and styrene.

Toluene is ototoxic in rats producing loss of cochlea hair cells which is considered to be an irreversible effect. However, effects have been insufficiently documented to enable determination of a NOAEC. Hearing loss has been reported in humans, especially when toluene exposure is associated with high exposure concentrations and a noisy environment. In addition there have been reports of disturbances of colour vision. Several epidemiology studies (Schaper et al, 2003, 2004) suggest that adverse changes do not occur when exposures are maintained below the current indicative occupational exposure limit of 50 ppm (188 mg/m3).

Repeated inhalation exposure to ethylbenzene causes ototoxicity in rats (Gagnaire et al, 2007). Auditory dysfunction is characterised by an elevation of hearing thresholds in the mid frequency range and loss of cochlear outer hair cells, the sensory cells in the inner ear. Hearing loss and cell damage increased with exposure concentrations. The NOAEC for ototoxicity was extrapolated to be 114 ppm (500 mg/m³) based on destruction of outer hair cells.

Inhalation exposure to styrene in animals produces ototoxicity in rats. The EU transitional RAR has identified a NOAEC of 50 ppm in humans based on colour vision discrimination effects in occupationally exposed workers.