Effects of exposure to trichloroethylene and noise on hearing in rats

Four groups of rats (n=8 per group) were exposed to either 3000 ppm trichloroethylene (TCE) alone or to 95 dB SPL noise alone or to the combination of TCE and noise or to control conditions. Exposure was carried out 18 hours/day, 5 days/week for 3 weeks. Exposure to TCE alone resulted in hearing loss at 4, 8, 16 and 20 kHz, but not at 24 and 32 kHz. Hearing loss due to exposure to noise alone occurred at frequencies of 8, 16 and 20 kHz. In general, combined exposure to TCE and noise resulted in larger auditory threshold changes than that produced by either TCE alone or noise alone when measured 1 and 2 weeks after the completion of exposure. For frequencies of 8, 16 and 20 kHz, hearing loss due to combined TCE-noise exposure was not larger than the algebraic sum of hearing loss due to exposure to TCE or noise alone. However, at a frequency of 4 kHz, hearing loss due to combined exposure was significantly larger than that produced by TCE exposure alone or noise alone, which itself had no effect at this frequency. These results suggest evidence of an interaction of combined exposure to TCE and noise at the lower edge of the range of frequencies affected.