Organic solvents are frequent air contaminants in industry and are found, for example, in paints, lacquers and printing inks. They are used in the production of furniture, plastics, fibres and rubber tyres. Over recent decades several studies in animals and humans have reported upon the effects of these substances on the auditory system and their interaction with noise. Potentially, this issue has significant socio-economic implications, as the chemical industry is the third largest industry in Europe, employing 1.7 million people directly and with 3 million jobs depending on it.

Studies on rats suggest that several organic solvents, for example, styrene and toluene, damage the cochlea (predominantly the supporting and outer hair cells (OHCs)) resulting in mid-frequency hearing loss.1 Retrocochlear or central hearing damage, although likely, has not been demonstrated clearly so far. Styrene can increase noise damage at levels as low as 300 ppm, and toluene at 1100 ppm. These were the lowest concentrations studied in animals, but it cannot be guaranteed that even lower levels are safe. However, assuming a safety factor of 10 and extrapolating these data to humans, the lowest observed adverse effect level (LOAEL) for styrene would be 30 ppm, whereas the occupational exposure limit for styrene is set much higher than this in several countries.

Synergistic effects occur in rats exposed to both noise and solvents.1 Solvents may modify the membranous structures of the OHCs, making them more fragile and vulnerable to noise. However, in combined exposures, the most important factor for inducing …