Possible Effects of Chemical Exposure on Hearing

ear structureAccording to an article in Occupational Health & Safety, certain industrial chemicals in common use are ototoxic (poisonous to the ears), meaning that they can damage hearing just as easily as industrial noise. However, simultaneous exposure to noise and ototoxic chemicals is particularly insidious because of their synergistic effect.

The article goes on to say: “Most ototoxins damage hearing through toxic oxidative stress, the same condition caused by prolonged exposure to high noise levels. Oxidative stress is an accumulation of reactive oxygen species (free radicals) brought about by excessive metabolic activity. This condition triggers a form of programmed cell death called apoptosis (the process is depicted in the accompanying graphic). While apoptosis occurs naturally as a part of healthy cell maintenance, a localized avalanche of cellular death—say, within the inner ear—causes extensive damage from which the body cannot properly recover.”

“Ototoxic compounds can affect all of the inner ear structures, including the balance organs—not just the hearing part—putting a person at risk for falls from a general loss of balance, dizziness, or, in severe (but rare) instances, vertigo. It is also important to remember that any chemical that is ototoxic is also likely to be poisonous to the kidneys, because the inner ear and the kidneys arise from the same germ layer during embryonic development.”

“While kidney damage is rare, it can result from a serious complication of chemical exposures and is often presaged by hearing difficulties resulting from the same causes.”

According to the European Agency for Safety and Health at Work (2009), experiments with rats have shown that combined exposure to noise and solvents induced synergistic adverse effects on hearing.

According to OSHA’s Appendix D— Combined Exposure to Noise and Ototoxic Substances – interactive effects may be observed, depending on the parameters of noise (intensity, impulsiveness) and the solvent exposure concentrations. In cases of concomitant exposures, animal studies suggest that solvents might exacerbate noise‐induced impairments even though the noise intensity is below the permissible limit value.