Cochlear injuries induced by the combined exposure to noise and styrene

The risk of hearing loss associated with occupational exposure to organic solvents mixture with and without concurrent noise exposure: A systematic review and meta-analysis

“…A total of 15 epidemiological studies [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], from 2 cohort studies [27,33], and 13 cross-sectional studies, with information on a total of 7530 workers (6% female) were published to publicize estimates of the association between independent or combined exposure to noise and mixture of organic solvent and developing hearing loss were eligible for inclusion in the organic solvent mixture concentration has exceeded the threshold limit [46]. Since in most of the previous studies the mean concentration of each solvent was below or slightly above occupational exposure limits, we employed 3 categories (EI < 0.5, EI = 0.5-1, EI > 1) to analyze the dose-response relationship between the level of exposure to the mixture of organic solvents and the risk of developing hearing loss.…”

“…These values indicate a higher effect of combined exposure to noise and solvents mixture on the risk of developing hearing loss. Previous epidemiological studies, indicate that an observed additive or even synergistic effect occurs from having combined exposures to noise and organic solvents mixture, by 2 to 11 times increase in the odds ratio of hearing loss [20][21][22][23][24][25][26]28,31]. It has been demonstrated that there is a synergistic causal effect caused by concurrent exposure to organic solvents mixture and noise in animal models [35].…”

“…Most human studies have shown that solvents mixtureinduced hearing loss, with or without exposure to noise, is predominantly associated with an increased risk in higherfrequencies (3, 4, 6 and 8 kHz) [15,18,[23][24][25][26][27]34] and it covers almost the entire region of frequencies tested, including the mid frequencies (2-8 kHz) when assessed by PTA. This, however, may be dependent upon the type of solvent to which the worker is exposed [7].…”

“…However, it has been shown that moderate exposures to organic solvents mixture (below or around the occupational exposure limit (OEL) for each solvent), increase the odds ratio of developing hearing loss [25]. Those who are exposed to concentrations much above organic solvents OELs, there is a linear dose-response relationship between exposure level, the risk of hearing loss and hearing threshold at high frequencies (in principle 8 kHz), the odds ratio for hearing loss was 1.004 for each increment of the index of lifetime exposure to solvents [23].…”

Noise-induced changes in cochlear compression in the rat as indexed by forward masking of the auditory brainstem response

“…These results are consistent with the human behavioral data collected by Oxenham and Plack (1997) from subjects with sensorineural hearing losses. The underlying pathology for the NIHL in the rats from the current study can be attributed heavily to pathology of the OHCs (Chen and Henderson, 2009) in the form of a combination of dead OHCs and living OHCs that are dysfunctional (Chen and Fechter, 2003). No specific underlying pathology was identified in the human subjects in whom FWM was tested (Oxenham and Plack, 1997), but with an identified cochlear origin, some OHC pathology can be considered likely.…”