Chemical exposure and hearing loss.

Workers are commonly exposed to multiple factors and substances that are hazardous to health. For instance, in 2005, approximately 30% of the European workers reported being exposed to noise during at least a quarter of the time spent in their work environment, 11% reported inhaling vapors such as solvents and thinners; 19% reported exposure to smoke, fumes, powder, or dust; and 14% reported handling chemical substances.1 Although occupational noise exposure has long been recognized in the United States and in Europe as the most deleterious factor to hearing2,3 the impact of chemical-induced hearing loss on workers should not be underestimated.4 A cursory survey of the literature for the last three decades reveals that concern about the effects of chemicals on hearing has grown steadily. The proliferation of work-related substances and medicinal drugs (mostly antitumor drugs and aminoglycosides) has been accompanied by an equivalent increase in the number of scientific publications on the hearing risks encountered by chemical-exposed persons. Cause for concern is even greater when the synergistic risks of co-exposures are considered. For example, physiological factors may increase the severity of a chemical’s effect on hearing. Today, robust evidence also confirms that the effects of ototoxic substances on ear function can be aggravated by noise, which remains a well-recognized cause of hearing impairment. In an expert forecast supervised by the European Agency for Safety and Health at Work5 (EU-OSHA, 2009), a “combined exposure to noise and ototoxic substances” was rated as an emerging risk.