Introduction Hearing loss in occupational exposure to a solvent mixture has been already reported; however, mixture in those reports did not contain ethylbenzene, a compound showing peripheral ototoxicity in animals exposed to high levels. In this work, we evaluated the auditory brainstem pathway in two samples of workers exposed to different levels of a solvent mixture where ethylbenzene was present, compared to a reference group.

Material and methods Individual exposure levels for up to seven compounds were obtained in two groups: Exposed (n=21 gas station attendants, GS, and leather shoe factory workers, LS) and Non-exposed (n=21, administrative workers) all of them from the city of León Guanajuato, México. The click-evoked auditory brainstem response test was performed in both groups.

Results Toluene, n-hexane, acetone, ethylbenzene, xylene and methyl ethyl ketone exposure levels were higher in LS (p<0.001). Only n-hexane exposure levels were above the permissible levels, while mean ethylbenzene exposure levels ranged 0.4–14.58 mg/m3. Wave V latency at four different points of stimulation for both ears was delayed in the exposed group, as well as the I-V and I-III interwave latencies at 70 dB (p<0.05). LS workers showed a delayed I-III interpeak interval compared to non-exposed group. Also in LS, ethylbenzene exposure levels showed a significant correlation with wave V latency at 40 dB (r=0.8, p=0.008).

Conclusion Our results point out to a central affection in the auditory system caused by ethylbenzene in a dose response manner. Workers exposed to ethylbenzene levels far below the permissible exposure limit should be closely monitored for early ototoxicity effects.