The effects of industrial ototoxic agents and noise on hearing

Recent epidemiological and laboratory experimental studies have established that some commonly used organic solvents and heavy metals can be ototoxic. Workers exposed to these substances may also be exposed to high levels of industrial noise. -- The possibility of short or long term combined exposure to noise and chemicals poses new questions for hazard risk assessment. This research project reviews aspects of the scientific literature on potential industrial and environmental ototoxic agents and, where possible, on the combined effects of multiple exposures. Multiple exposures may be exposures to mixtures of chemicals, sequential exposures to chemicals or exposures to chemicals and noise sequentially or simultaneously. -- Organic solvents implicated are unsaturated aliphatic or aromatic compounds including toluene, styrene, xylene, trichloroethylene and carbon disulphide and the heavy metals include lead, mercury and tin. -- Animal and human studies of the effects of these substances on hearing are reviewed. Particular attention is devoted to combined effects. Some data on other possible ototoxic chemicals are reviewed. -- The study finds that there are similarities in the effects of various solvents on the cochlea and that there are neurotoxic effects of variable severity. Interactions between noise and chemicals are described. -- There is some information on the effects of those agents at the cellular and biochemical level especially for mercury and tin. Generally, however knowledge of the biochemical and pharmacokinetic basis for ototoxicity was found to be quite limited. -- Studies of chemicals and noise together in both humans and animals confirm the need for watchfulness in occupational health and safety regulation and rigour in enforcing existing exposure standards for both noise and chemicals especially where there is the possibility of multiple exposures.