Comparison of toluene-induced and styrene-induced hearing losses

Toluene and styrene are industrial solvents that can severely damage the au ditory function in adult rats. In the present study, toluene (1000 to 2000 ppm) and styrene doses (500 to 1500 ppm) were investigated according to the same schedule: 6 hours per day, 5 days per week, for 4 consecutive weeks. The auditory function of the animals was tested by recording evoked potenti als from the inferior colliculus over a frequency range from 2 to 32 kHz, w hereas pathological data were evaluated by conventional histologic techniqu es. The permanent threshold shifts (PTS) were obtained with a styrene dose 2.4 times lower than that of the toluene. The slope of the regression line (PTS/doses) was 2.1 steeper with styrene than that obtained with toluene in the same experimental conditions. The sequence of histopathological events along the organ of Corti, especially the orderliness and the location of t he traumas, was similar for paired concentrations of styrene and toluene, w hich were respectively 650 ppm, 1500 ppm for the first match, and 850 ppm, 1750 ppm for the second one. Both electrophysiological and histological fin dings point out the higher ototoxic potency of the styrene compared to that of the toluene. Assumptions concerning the ototoxic mechanism are addresse d in the present paper. (C) 1999 Elsevier Science Inc. All rights reserved.