The effect of Lead and Noise on Noise-induced Hearing Loss at 4 kHz Frequency: an experimental study

Hearing loss is an occupational chronic disabling and is due to complex processes of numerous risk factors such as excessive noise, ototoxic agents, aging. We aimed to examine the concurrent effect of lead and noise on rats' noise hearing function as a sub-acute exposure.

In this experimental study, 40 male rats were divided into 4 groups as 1) control group 2) exposed to 105 dB noise at 4 kHz frequency 8h/day, 6day/week for 4 weeks 3) exposed to 4 mg/kg lead acetate by gavage 6day/week for 4 weeks 4) exposed to both lead and noise. Blood lead levels were evaluated by Graphite Furnace Atomic Absorption Spectrometry. In addition, before and after exposure, the auditory brainstem response (ABR) was performed to examine the hearing loss in rats.

The hearing threshold at noise exposure (105 dB at 4 kHz frequency) group indicated a significant increase (10 dB and 11.5 dB with click and tone burst stimuli, respectively) compared to the control group (p<0.0001). Moreover, there was a significant difference between the lead concurrent noise-exposed group and the control group regarding the latency of waveform II with both stimuli (p<0.0001). There was a positive correlation between Blood Lead Level in lead-treated rats with Auditory Brainstem Response threshold by tone burst stimulus (r = 0739, p = 0.015).

we concluded that lead and noise have a synergistic effect and can exacerbate hearing loss. However, additional studies at various doses are needed to confirm this finding.