|Morata, Thais C
|Research conducted over the last two decades has brought attention to the ototoxicity
of chemicals in the workplace and their interaction with noise. Chemicals
that have been specifically studied for their ototoxicity include solvents, metals,
asphyxiants, PCBs and pesticides.
Noise exposure is particularly damaging to the cochlea, a part of the peripheral
auditory system, whereas chemicals tend to affect both the cochlear structures and
the central auditory system. Reduced blood flow and free radical formation are important
ototoxic mechanisms shared by noise and chemical exposures. Solvents
and asphyxiants may also disrupt intrinsic anti-oxidant defences and make the ear
more vulnerable to the effects of e.g. noise exposure.
The chemicals reviewed in the present document have all been associated with
auditory effects in animals. Some of the solvents and the asphyxiants interact
synergistically with noise or potentiate noise effects on the auditory system. Combinations
of chemical exposure with noise and other stressors such as physical
activity during exposure may lower the concentration of the chemical exposure
necessary for induction of an auditory effect.
Auditory effects have also been indicated in humans for all agents covered in
this document for which there are data. Noise is often present in the occupational
arena, which makes prediction of the outcome challenging.
As combined exposure (e.g. chemical and noise) is currently not taken care of in
the regular occupational exposure limit (OEL) setting procedure, a noise notation
can be used to indicate an increased risk of hearing loss after exposure to the
chemical at a level close to the OEL with concurrent noise exposure. The strength
of evidence for ototoxicity differs between the agents but falls basically into three
categories, i.e. agents for which:
1) human data indicate auditory effects under or near existing OELs and robust
animal data support an effect on hearing from exposure (styrene, toluene,
carbon disulphide, lead, mercury and carbon monoxide),
2) human data are lacking whereas animal data indicate auditory effects under
or near existing OELs (p-xylene, ethylbenzene and hydrogen cyanide),
3) human data are poor or lacking and animal data indicate an auditory effect
well above the existing OELs (chlorobenzene, trichloroethylene, n-hexane,
n-heptane, some solvent mixtures, trimethyltin, acrylonitrile, 3,3'-iminodipropionitrile,
pesticides and PCBs).
|Arbets- och miljömedicin, Göteborgs universitet
|Arbete och Hälsa, Vetenskaplig skriftserie
|asphyxiant, auditory, hearing, metal, noise, occupational exposure
|limit, ototoxic, PCB, pesticide, review, risk assessment, solvent
|142. Occupational exposure to chemicals and hearing impairment.