Effect of Interaction between Noise and Toluene on Auditory Function in the Rat

Abstract

Rats were exposed to toluene (1000 ppm, 16 h/d, 5 d/w, 2 w), or noise (100 dB Leq, 10 h/d, 7 d/w, 4 w) or toluene followed by noise. Auditory function was tested by brainstem audiometry using a 1/3 octave filtered sine wave stimulus at the frequencies 1.6, 3.15, 6.3, 12.5 and 20.0 kHz. A high-frequency auditory impairment was observed after exposure to toluene alone and noise alone. A slight recovery was recorded 1 and 6 months after the toluene exposure. Toluene followed by noise resulted in a higher threshold at all frequencies. A slight recovery was recorded 6 months post-exposure. The threshold shift exceeded the summated loss caused by toluene alone and by noise alone, particularly at 3.15 and 6.3 kHz. The latencies varied only slightly. The results indicate that the major cause of the auditory impairment was cochlear damage and that only minor injury was caused to the auditory pathways.

Effects of occupational exposure to organic solvents and noise on hearing.

“…Toluene ototoxicity has been discus sed previously. Evidence indicating that toluene exposure affects hearing comes mainly from studies conducted with toluene abusers (21)(22)(23)(24) and animal s (8,(27)(28)(29)(30)(31). In rats toluene interacted synergistically with noise.…”

“…In the United State s at least one million workers in manufacturin g are estimated to have sustained job-related hearing impairment , and about a half million of the se work er s have moderate to severe he aring imp airment (I ). Occupation al hearing loss has long been reco gnized as a direct health effect of overexpo sur e to nois e, but only recently has expo sure to solv ent s been con sidered as a contributor to the development of hearing impairment (4)(5)(6)(7)(8)(9)(10). There is evidence wh ich suggests that noise interact' > synerg istica lly with various drugs and chemicals (11)(12)(13)(14)(15)(16)(17)(18).…”

Chemical exposure and hearing loss

“…: Experiments with rats have shown that combined exposure to noise and solvents (such as toluene, styrene, and ethylbenzene) induces synergistic adverse effects on hearing. [77][78][79][80][81] In most of these investigations, high concentrations of solvents were used for short intervals of time, conditions which do not accurately reflect occupational exposure conditions.…”

Hazards to Hearing from Combined Exposure to Toluene and Noise in Rats

“…A large number of studies have examined the nature of the interaction between noise and organic solvents and its impact on hearing in animal experiments. A potentiation of the auditory impairment was found in rats exposed sequentially to toluene (1000 ppm 16 hours/day, 5 days/week for 2 weeks) and noise (100 dB L eq 10 hours/day, 7 days/ week for 4 weeks) when toluene exposure preceded noise exposure [5]. A reverse exposure order resulted only in an additive effect [30].…”

“…The possible ototoxic effect of toluene was fi rst reported in rats by Pryor et al [1], and subsequent studies demonstrated hearing loss in rats after exposure to toluene [2][3][4][5][6][7][8][9][10][11], styrene [8,[12][13][14][15][16][17][18], xylene [8,9,12], ethyl benzene [19,20], trichloroethylene [8,9,[21][22][23][24], chlorobenzene [9], and n-heptane [25]. The ototoxic potency of the different solvents varies signifi cantly [9,14,26], but when rats were exposed to different combinations of organic solvents, the auditory impairment was additive with respect to the potency of the solvents under study [9].…”