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Ototoxins: A New Concern
The hazardous effects of noise are well known, and most companies now have active hearing conservation programs to protect their workers. Less understood, but receiving more attention in recent years, are the effects of occupational ototoxins (ear poisons) on hearing. Ototoxic chemicals can cause hearing loss independently, and may even work together with noise to accelerate, or increase, the risk of hearing loss.
Potential ototoxicity of workplace chemicals first came to the attention of researchers in the 1970s and 80s; however, comprehensive studies and clear conclusions about the hazards are still in the making. It appears that certain chemical substances show ototoxic effects when airborne; other ear poisons are absorbed through the skin. Some ototoxins affect the inner ear in the same manner as noise; others target "higher" parts of the auditory system such as the auditory nerve, cortex, and brainstem centers. In industry, because noise is often present where chemical exposures occur, it can be difficult to separate the degree of hazard associated with each agent.
Some of the occupational compounds implicated as being ototoxic:
• Ethyl Benzene
• Carbon monoxide
• Hydrogen cyanide
Jobs where ototoxins and noise often combine:
• Manufacturing of metal, leather, and petroleum products
• Fueling vehicles and aircraft
• Pesticide spraying
Currently there are no regulations requiring monitoring of a worker's hearing due to occupational exposure to ototoxic chemicals. However, appropriate use of a respirator and/or skin protection can protect against chemical exposures while effective hearing protection can protect against noise. Proactive companies are beginning to take into account special cases of combined noise/chemical exposures in the workplace. To learn more, check out these helpful resources:
European Agency for Safety and Health at Work (2009). Combined exposure to noise and ototoxic substances (literature review).
Morata TC, Little MB (2002). Suggested guidelines for studying the combined effects of occupational exposure to noise and chemicals on hearing. Noise Health; 4:73-87.
The National Research Council (2014). Review of Styrene Assessment In the National Toxicology Program, National Academies Press.
OSHA (2013). OSHA Technical Manual, Section III: Chapter 5, G. Noise and Solvent Interactions (Updated 08/15/2013).
Themann C, Suter A, Stephenson M (2013). National Research Agenda for the Prevention of Occupational Hearing Loss—Part 1. Semin Hear; 34(03): 171-173.
US Army Public Health Command Fact Sheet 51-002-0713, Occupational Ototoxins (Ear Poisons) and Hearing Loss.