Noise-induced hearing loss was listed in 1991 as one of the 64 sentinel health events that cause preventable disease and disability in workers. [Mullan, p. 782] In recent years, concern has been raised about the impact of organic solvents such as toluene and styrene on occupational hearing loss. "While the ototoxicity of both solvents is clearly demonstrated in rat studies, their ototoxic potency in humans is not well characterised yet." The rat experiments showed a NOAEL of about 300 ppm for styrene and about 1000 ppm for toluene. The current workplace limits are 20 ppm for both styrene and toluene, and the IDLH levels are 700 ppm and 500 ppm respectively. [
PMID 18259983] "On the whole, studies on employees in various branches of industry gave inconsistent results. Indeed, a clear relationship between solvent and hearing impairment is difficult to assess with epidemiological studies . . . " [See Hyperlink] "Due to missing toluene effects, it was concluded that the threshold level for developing hearing loss as a result of occupational exposure to toluene plus noise might be above the current limit of 50 ppm toluene." [
PMID 19042192] In a review published by IRSST, only four chemicals (lead, styrene, toluene, and trichloroethylene) were designated as "ototoxic substance." Of these four, only lead had "evidence of interaction" with noise. [www.irsst.qc.ca] As a risk factor for occupational hearing loss, chemicals are a "low risk"; the level of evidence is "low." [
PMID 26249711] "Therefore, the exclusive effect of toluene or styrene exposure on hearing could not be determined based on these studies." [
PMID 33275083] "We found no evidence of an association between organic solvents and tinnitus; however, there was evidence of an association between organic solvent exposure and prevalence of high-frequency hearing loss." [
PMID 30806784] "See "Noise-induced hearing loss."