Simultaneous exposure to ethyl benzene and noise: synergistic effects on outer hair cells

The effects on hearing of simultaneous exposure to the ototoxic organic sol vent ethyl benzene and broad-band noise were evaluated in rats. The effects of three ethyl benzene concentrations (0, 300 or 400 ppm) and three noise levels (95 or 105 dB(lin) SPL or background noise at 65 dB(lin) SPL) and al l their combinations were investigated for a 5 day exposure at 8 h/day. Dis tortion product otoacoustic emissions and compound action potentials were a ffected after 105 dB noise alone, and after 105 dB noise in combination wit h ethyl benzene (300 and 400 ppm). However, the amount of loss for these co mbinations did not exceed the loss for 105 dB noise alone. Outer hair cell (OHC) loss after exposure to 300 ppm ethyl benzene was located in the third row of OHCs. At 400 ppm, the loss spread out to the second and first row o f OHCs. Noise alone hardly affected the OHC counts except for a minor loss in the first row of OHCs after 105 dB SPL. Noise at 105 dB in combination w ith ethyl benzene at 300 and 400 ppm, however, showed OHC loss greater than the sum of the losses induced by noise and ethyl benzene alone. (C) 2001 E lsevier Science B.V. All rights reserved.