Hearing Protection

Chemicals Causing Hearing Loss: Ototoxins

chemical hearing loss ototoxinsMany common chemicals can cause hearing loss, tinnitus, deafness and vertigo, with people often unaware of the health risks despite being at risk of exposure.

Ototoxic chemicals, which can be found in substances such as paints, thinners, degreasers, glues and engine exhaust, travel through the blood stream once they have entered the body and can result in damage to the auditory nerves or the cochlear in the inner ear.

Current estimates suggest that more than 750 chemical groups are potentially ototoxic, including some medications, although studies have only analysed a few of them in depth.

The prevalence of combined noise and chemical exposure in workplaces is one of the reasons why research into chemical-induced hearing loss has only started to receive increased attention in recent decades.

Exposure to both noise and ototoxins increases the likelihood of hearing damage however Australian exposure standards have not yet been revised to take this into consideration.

Until standards are updated, the Managing Noise and Preventing Hearing Loss at Work Code of Practice recommends that the daily noise exposure for workers with a dual noise and chemical exposure is reduced to 80 decibels or less (the maximum exposure is usually 85 decibels) and that audiometric testing and information on ototoxins is provided to workers.

Regardless of noise exposure, the Code of Practice recommends workers with an airborne exposure to ototoxins of 50% or more of the chemical’s exposure standards should receive an annual audiogram.

If there is no air monitoring, then annual audiograms should be carried out when exposure is difficult to estimate, ventilation efficiency is unknown or when workers report health concerns that may be due to ototoxins.

 

Ototoxic Substances and Their Symptoms

Workplace ototoxins can be divided into three major categories: solvents, heavy metals and asphyxiants.

Ototoxins enter the body by inhalation, skin absorption and ingestion.  Those which can be absorbed through the skin are considered particularly hazardous because of the increased exposure risk.

Aside from varying degrees of hearing loss and the ringing in the ears known as tinnitus, ototoxins can also cause balance problems.

Some symptoms that indicate this might be occurring are headaches, dizziness, blurry or changed vision, feeling lightheaded or weak, an inability to walk or walking with legs far apart to steady yourself, difficulty moving your head, problems walking in the dark and feeling a ‘fullness’ in the ear.

 

Dangerous Industries and Risk Reduction

Dangerous industries include painting, boat building, construction, furniture making, printing, metal, fibreglass and leather production, aircraft maintenance, fuelling vehicles and aircraft, radiator repairs and pesticide spraying.

Substitution, isolation and local ventilation are some controls which should be applied to prevent or reduce harmful exposure, with personal protective equipment (PPE) appropriate to the chemical, such as face masks or gloves, used to reduce skin and respiratory absorption where other measures are insufficient.

Other control measures which can be implemented include substituting water-based products instead of solvent-based products, education about the chemicals being used and their risks, and following all the safety directions for the specific chemical in use.

Some workplace ototoxic substances are listed in the table below:

 

Note: italics indicates that the substance can be absorbed through the skin
Solvents Metals Asphyxiants
Butanol Arsenic – parasites, microorganism inhibiters Acrylonitrile
Carbon disulphide – pesticides Lead Carbon monoxide – vehicles, cigarette smoke, welding, gasoline tools, cooking stoves, clothes dryers
Ethanol Manganese Hydrogen cyanide
Ethyl benzene Mercury Organophosphates
n-heptane Organic tin Paraquat
n-hexane    
Perchloroethylene
Solvent mixtures and fuels Stoddard solvent (white spirits)
Styrene – plastics, insulating material
Toluene – paints, lacquers, adhesives, rubber, leather tanning, spray paint and other products
Trichloroethylene – dry cleaning, spot remover, rug cleaners, paints, waxes, pesticides, lubricants
Xylenes – paints, varnishes, thinners

Sourced from information contained in the Managing Noise and Preventing Hearing Loss at Work Code of Practice, Appendix A and the Audiology Information Series: Chemical Exposure Effects on Hearing and Balance.