[Interaction between noise and ototoxic agents in the work environment]

There is a large number of well known substances, which exert an ototoxic effect in industrial settings. Ototoxic agents may be involved in many interactions with noise, the main factor responsible for the development of occupational hearing loss. Owing to the complexity of these relationships, their assessment is easier if controlled trials are carried out on animals. However, the results of experimental studies apply to high exposure levels, which are very rarely observed in industrial conditions. Data useful in estimating risks of hearing loss induced by industrial exposure are scarce. Until quite recently, the studies have focused on the combined effects of noise and chemicals of such groups as organic solvents, carbon monoxide or heavy metals. In the former group, a synergistic effects of noise and carbon disulfide as well as noise and toluene have been revealed at the cochlear level. Interactions between these chemicals and noise at the higher levels of the auditory system are most likely of an additive nature. Synergistic effect of carbon monoxide and noise may occur only at high concentrations of this substance. It is believed that the mechanism responsible for the interaction between carbon monoxide and noise depends on the hypoxemic effect of the former. A diminished access to oxygen exacerbates noise-induced metabolic disorders. However, it should be stressed that the nature of an interaction may be rather complex, because carbon monoxide (contrary to noise) also induces retrocochlear damage. As to the combined exposure to heavy metals and noise (range, 68-72 dB), the occurrence of cardiotoxic effects, not observed in single exposure to those agents, has been found in experimental studies. This may evidence a potentially wider range of possible interactions between toxic agents and noise not only in respect of the hearing organ. In further studies it seems essential to find out to what extent the effect of ototoxic agents should be taken into account in assessing the risk of hearing loss in industrial settings. If the effects of these agents in the work environment are taken into account then it will be necessary to verify the medical prevention criteria and hygiene norms regarding noise exposure.