The comparison of effects of toluene, especially noise and toluene along with noise per Auditory Brain Stem response on rabbit

Background: An increase more than definite limit in sound pressure level is harmful for health,
mean while, organic solvents like toluene are used in industrial processes with noise widely. So, this
study was going to investigate the relationship between toluene (1000 ppm), noise and toluene
along with noise (frequencies 4000 and 8000 Hz) per auditory Brain Stem response (ABR) on
rabbits being exposed to these contaminants.
Materials and Methods: This survey was done in experimental method on 48 three months old,
male adult white New Zealand rabbits (1800±200 g body weight), in nine groups which were
exposed to toluene(1000 ppm), noise (4000Hz), 100 dB SPL, combination of toluene and noise
(4000Hz), noise (8000Hz) and combination toluene and noise (8000Hz). ABR test measurement was
conducted using click and tone burst stimuli in 110dB sound pressure level. Then the results of ABR
test of groups exposed were analyzed by SPSS software. One-way variance (ANOVA) analysis was
used to compare the groups and Tukey test was applied as a post hoc test for comparison among
the groups. P values were obtained by Tukey test. t-test was conducted for comparison of ABR test
results after and before exposing groups. Differences at the level of P<0.05 were considered
statistically significant.
Results: The results of the study showed that Exposing rabbit's to combination of toluene and
noise caused hearing impairment in all of frequencies auditory especially in frequencies 250, 500
and 1000Hz. So that, wave five in ABR test (tone burst stimuli) didn’t formed in 250-1000Hz
frequencies. The mean of latency time of V wave (5 wave) were as follows; In control group
4.84±0.07ms, group exposed to toluene 5.18±0.07ms, noise group (4000Hz) 5.5±0.07ms and in
combination noise and toluene group (4000Hz) 5.79±0.07 ms. The mean of latency time of V wave
in control was compared to that of group noise group P=0.01, toluene group P=0.07 and
combination noise and toluene group P=0.0001.
Conclusion: According to the result of this study, Both toluene and noise exposure caused the
rabbits in hearing impairment but combination of toluene and noise exposure in frequencies of
4000 Hz and 8000Hz was much worse than hearing impairment. So that, the ABR test on rabbits
didn't formed V wave in low frequency.