Effects of noise exposure in combination with exposures to JP-8 jet fuel

Abstract

The objective was to evaluate the potency of JP-8 jet fuel to enhance noise-induced hearing loss using inhalation exposure to fuel and simultaneous exposure to noise with male & female Fischer 344 (F344) rats for 6 h/d, 5 d/wk for 4 wk (200, 750, or 1500 mg/m3). Parallel groups of rats also received nondamaging noise (85 dB) in combination with fuel, noise alone (75, 85, or 95 dB), or no exposure to fuel or noise. Computer software was used to generate a pure and precisely filtered white noise file of one octave band, centered at 8 kHz. The filtered file was then played through electrodynamic shakers that induced vibration from the outside in the metal plenum at the bottom of each exposure chamber to produce noise. Significant concentration-related impairment of auditory function measured by distortion product otoacoustic emissions (DPOAE) and compound action potential (CAP) threshold was seen in rats exposed to combined JP-8 (1500 mg/m3) plus noise (85 dB) with trends toward impairment at 750 mg/m3 JP-8 plus noise (85 dB). JP-8 alone exerted no effect on auditory function. Noise was able to disrupt DPOAE and increase auditory thresholds when noise exposure was at 95 dB. Two additional studies with JP-8 (1000 mg/m3) and noise (85 dB), one with F344 rats and one with Long Evans rats did not affect auditory function. However, a pilot assessment indicated a central auditory processing dysfunction (i.e., impaired brainstem encoding of stimulus intensity) among F344 and LE rats exposed to JP-8 alone and JP-8 with noise.