Ototoxicity of Organic Solvents - From Scientific Evidence to Health Policy

Abstract

The scientific workshop, organized under the 6th European Framework Programme, the Marie Curie Host Fellowship for the Transfer of Knowledge "NoiseHear" Project, by the Nofer Institute of Occupational Medicine (Łódź, Poland, 15-16 November 2006), gathered world specialists in noise, chemicals, and ototoxicity, including hearing researchers, toxicologists, otolaryngologists, audiologists and occupational health physicians.The workshop examined the evidence and the links between isolated exposure to organic solvents, combined exposure to noise and solvents, and effects on the auditory system. Its main purpose was to review the key scientific evidence to gather the necessary knowledge for developing adequate occupational health policies. This paper summarizes the workshop sessions and subsequent discussions.

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

“…Several animal studies have confirmed that exposure to combinations of some solvents (mixtures of solvents) will contribute to greater hearing loss than it was found in single-solvent exposures [49][50][51][52][53]. The human studies have also confirmed such results [35]. The assessment of dose-response relationships are usually challenging and demanding.…”

“…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]. However, in the case of human studies, the possible synergism of combined exposure to solvents and noise on hearing has not been consistently identified [7].…”

“…Solvent-induced hearing impairment for humans not only involves the inner ear but also the central nervous system. Although there is strong research evidence that excessive generation of oxidative stress products are the underlying cause of developing hearing loss, animal studies also suggest that there are differences in mechanisms of solventinduced and noise-induced hearing loss in the cochlea in a way that solvents usually cause chemical poisoning, whereas noise causes mechanical damage [35]. Due to the fact that concentrations of organic solvents in occupational settings are usually much lower than the ones used in animal studies, it is more difficult to make a conclusion about their ototoxic effects of these solvents [48].…”

“…Workers from a wide range of industry sectors are usually exposed to mixtures of xylene, toluene, benzene, methyl ethyl ketone (MEK), methyl isobutyl ketene, ethanol, ethyl acetate, butyl acetate, ethyl benzene, cyclohexane, etc. The most prevalent exposures seem to happen in industries where workers have contacts with paints, thinners, lacquers and printing inks [35]. Although not well recognized in the case of humans, the ototoxic effects of organic solvents have been widely studied.…”

Noise and lead exposures at an outdoor firing range - California.

“…Although none of the ingredients listed on the MSDS that were given to us had been observed as ototoxicants, users should be aware that moderate exposures (below or around the OEL) to solvents such as toluene [Morata et al 1993;Chang et al 2006], xylene, and mixtures of solvents [Sliwinska-Kowalska et al 2004;Fuente et al 2009] have been shown to be associated with hearing loss [Sliwinska-Kowalska et al 2007]. …”